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Power vent water heater troubleshoot
Troubleshoot power vent water heater
Basic power vent maintenance/ pdf
burner assemblypower vent water heaterTwo types of power vent water heaters
Power vent water heater (pictured on right) has one pipe connected to top of water heater, and derives all incoming air from inside the home and releases combustion gas in a sealed vent installed either horizontally through a side wall, or vertically through roof. Power direct vent has two pipes connected to top of water heater, one for intake and one for vent. Power direct vent derives all incoming air from outside the home through a sealed intake pipe and is vented through roof or side wall, with outside air supply coming from roof or side wall.

How power vent water heaters works
-The water heater must be plugged into and receiving 120 volts, range 115-125 volt, from a circuit without GFCI protection. The outlet must have correct polarity and grounding. Lack of ground will cause flame sensor failure and other problems. Low voltage, reversed polarity and GFCI cause various issues including short-cycling or continuous blower operation, or insufficient blower rotation.

-The gas valve controls the operation of heater, and issue error codes when operation encounters problem.
-The gas valve has a probe that extends into the water located on backside of valve. The thermostat probe contains 1) ECO energy cut off that trips when water inside tank reaches 188-199° depending of model of gas valve and 2) a thermistor. The thermistor is a heat sensitive variable resister. A change in water temperature changes the thermistor resistance (measured in ohms).
-The gas control valve interprets change in resistance as a change in temperature and uses information to activate and deactivate call for heat. Water temperature around the thermostat probe can drop 15-25° before heat cycle begins.

-When the heat cycle begins, the gas control valve closes a circuit that turns on the 120 volt blower located on top of water heater. 
-The blower pulls air up from the combustion chamber into vent pipe and begins a cycle of releasing toxic combustion by-products, including NOx SO CO CO2 and acidic water vapor, into the atmosphere, where it creates an exciting new future for the planet. Alternative for some: Connect solar panels to electric water heater

-The vacuum safety switch (also called pressure switch) is connected to blower via rubber tube. The rush of air through the vent pipe creates vacuum pressure. 'The vacuum switch is sensitive, so you can blow or suck a little on the tube and that will activate the switch.' 'If the vent has blockage, then back pressure will prevent switch from closing.
-The vacuum switch closes a circuit that tells gas control valve that blower is operating at speed, and it is safe to activate burner. This ensures the blower can evacuate combustion gasses and support complete burning of fuel. Complete burning is essential to prevent explosion hazard caused by ignitable fuel gathering inside combustion chamber or vent pipe. The efficiency of gas water heater combustion is typically 59-61% (when new), with the remaining 39-41% of heat going up the flue pipe. The wasted heat cannot be recaptured without risk of slowing proper venting. Option is to buy more expensive condensing heater with higher technology for recapturing heat but with higher maintenance costs. The blower can run up to 30 seconds before ignition of heater (called pre-purge cycle).

-If the 120 volt outlet has correct voltage, polarity and grounding, the gas valve electronic control board activates the hot surface igniter.
-The igniter is consumable and wears out ... If the igniter is not worn out, the wire connections are solid and undamaged, the igniter is not coated with carbon deposits (clean with emery cloth), and tests between 15.5 and 18.8 ohms, then the igniter will glow red with heat while gas is released down the burner tube (also called manifold tube), through the orifice into the burner head. The igniter can be inspected through the viewport.

-If the gas pressure good (observe operation of gas appliances when another appliance is turned on), and the orifice is clean and correctly sized, and hot surface igniter and burner head are clean (not sooted with black soot that indicates need for immediate service, including vent and air intake inspection, gas pressure check, incorrect orifice, gas leak at gas control, loose connection between manifold and burner and general combustion chamber cleaning) and burner is in good working order (reasonably quiet during combustion), and the igniter is correct distance away and positioned directly in front of a gas jet, then the gas will ignite (should ignite quickly) and gas will burn blue color with flicks of yellow and red as seen through the viewport (slow ignition, lazy yellow flame, noisy flame, or flame that lifts excessively off burner head indicate need for immediate service).
-When gas is ignited, if the flame sensor is correctly positioned, and not dirty (If  the flame sensor's metal is off color then change it out, or lightly clean with an abrasive cloth), then flame sensor confirms that flame is present and signals the gas valve to continue releasing gas.

-If  the flow of combustion and ventilation air is not blocked, and if there is adequate incoming air supply with enough oxygen to support combustion ... high elevation and high ambient air temps cause air molecules farther apart - thin air can starve gas appliances ... gas burning appliance requires the oxygen contained in 12.5 cubic feet of air (at sea level) for every 1000 BTU of heat generated, ... and if the igniter receives continuous power and glows red continuously during the entire heating cycle, then the burner remains on and water temperature inside tank begins to rise.
-Signs of insufficient air include yellow flame, sooted water heater parts ... and possible smell of burnt gas and carbon monoxide.
-When water temperature inside tank reaches set point, the gas control valve turns off gas to burner. Burner shuts off while blower continues running to evacuate remainder of combustion by-product (called the purge cycle or post purge), then shuts off. If the blower stays on, it is either a stuck air switch or bad gas control valve.

-If the water heater has pilot light instead of hot surface igniter, then the gas valve has a pilot tube in addition to the burner tube that connects to burner assembly. The gas valve releases gas into the pilot tube continually as long as thermopile is functioning and correctly positioned in the pilot flame so it sends small electric current to gas control valve, signaling that pilot flame is on. If the pilot is out, or thermopile is bad, then the gas valve receives no current, and will not release gas. If the pilot flame and thermopile are working correctly, the ignition sequence can begin once the blower operation is confirmed.

-If the blower is not operating, or running at lower speed because of a brownout or lack of voltage or malfunction, the vacuum switch does not receive enough vacuum pressure and will not close, and the ignition sequence will not take place. Plug blower directly into outlet to check function. Test electric power. Bring power from different outlet. Tap lightly on the switch to see if it closes. Avoid drywall, or construction sanding in same room, and avoid other dusty or dirty conditions that can clog pressure switch. You can NOT jump out (bypass using a wire) the pressure switch because gas valve requires the switch to have open condition before the blower gets energized ... This is to prevent folks from bypassing the vacuum switch and causing other problems such as unburned fuel inside a hot vent pipe, creating explosion and fire risk.

-The blower has a built-in, automatic resetting, thermal safety switch (also called vent over-temperature switch) that monitors temperature of the vent pipe. If temperature on vent pipe at the blower exceeds 160-180°, the thermal switch opens (shuts off) the circuit between gas valve and pressure switch, shutting down the heater. The gas valve thermostat turns off gas supply, blower turns off, the vacuum switch resets to open position. When vent pipe cools to 125°, the heat cycle begins again. Repeated failures in the ignition and heating sequence are recorded by the gas control valve. When errors exceed parameter, the gas control valve issues error code.

-The blower thermal safety switch  is designed to shut off heater if combustion gas reaches 160-180°. This prevents water temperature inside tank from reaching the 188-199° ECO limit of gas control thermostat. If temperature of water inside tank exceeds high limit set point, the ECO trips off, and gas control valve turns off all gas. Older style gas control valve may require replacement. Newer gas control valves can be reset (with exceptions) once repairs have been made to correct cause of overheating. If the thermostat comes out of calibration, and is no longer performing or reading correct temperatures, it requires replacement of gas control valve.

-If the thermostat is operating correctly and within calibration tolerances, then when temperature inside tank reaches the thermostat set point, for example 120°F ±5-10°, the gas control valve thermostat turns off gas to burner, and a moment later turns off blower. The water heater goes into standby mode until water temperature drops below thermostat set point again.
Power vent Back to 14 things for troubleshoot gas water heater
12) power vent water heater blower
Blower draws air into combustion chamber and then pushes combustion by-product through the vent pipe where it exits on roof or sidewall of home or structure.
Check blower assembly: Turn off power to water heater. Remove vent from top of blower. Disconnect pressure tube going to pressure switch, and attach a manometer to the pressure tap. Turn on power to the blower. Pressure should be 1.3" w.c. to 1.4" w.c. at normal altitude (3000 ft).

How it works: "When the thermostat senses a need for hot water, the control valve tests for 1) closed blower thermal temp switch, and 2) open pressure switch. If test fails, then gas control locks out and issues error code.
If test is passed, a valve is opened which allows gas to flow to the closed solenoid valve located inside the gas control valve. As gas pressure builds up within the solenoid, the gas pressure switch closes and 24 VAC flows to the blower relay. The blower relay contacts close and send 120 VAC to the blower which turns on. Air flow from the blower closes the air pressure switch sending 24 VAC to the solenoid valve. The solenoid valve opens and allows gas to flow to the burner which is lit by the pilot or igniter"

Blower power consumption: less than 5 amps @ 120 volt. 120 volt x 5 amp = 600 watts running with 1200 watts start-up.
Buy
Manometer

Resources:
Power vent water heater issues
Anode covered by power vent
How to test gas pressure on gas water heater
How to clean burner
water heater blower motor  Blower
Blower is connected to gas control valve with a wire (called the control cable).
The gas control uses a firing sequence to activate the blower and start moving air upwards just before the burner fires up.

Blower, control cable, gas control valve, and pressure switch are part of troubleshooting. Eliminate the obvious: Check the blower first, cable next, and gas control valve last.
Make sure blower is aligned on top of heater and the opening is not obstructed by gasket and gasket is not damaged.
Other issues: excessive vent length, vent blockage, high vent temperature, bad wiring inside junction box,

Buy blower:
Water heater blowers at Amazon

Blower troubleshoot
Test pressure switch
Power vent troubleshoot
Troubleshoot power vent hot surface ignition
How to check blower motor
Check blower motor
Example flue pipe chart, gives general rule of thumb for venting a power-vent water heater.

Rely on instruction manual for your specific model for the correct vent installation.
 
water heater blowers Blowers: Fasco, AO Smith, Bradford White, Rheem power vent water heater exhaust draft-induced blowers
Buy blower:

Water heater blowers at Amazon
Other types blowers
Fasco multi-purpose blowers
AO Smith multi-purpose motors and blowers
Furnace blowers
water heater pressure switchTroubleshoot Pressure switch / same as vacuum switch
Bypass or jumper around the pressure switch immediately after the inducer starts.
What does a vacuum switch do? What does a pressure switch do? The vacuum switch measures the vacuum created by the blower and verifies the blower is operating at speed. This ensures the blower can evacuate combustion gasses and support complete burning of fuel so no unburned fuel is inside the vent pipe.
Generally, to check if blower is good and pressure switch is bad, you bypass the pressure switch and connect blower directly to 120 volt outlet, running a pigtail to the blower or plugging blower directly into outlet.
At beginning of a call for heat, the vacuum switch is OPEN. The vacuum switch must close, like an ordinary on-off switch and complete a circuit that notifies gas control that blower is operating correctly.
Switch can fail to open if there is a vent obstruction or vent is too long. Correct venting.
"In troubleshooting pressure switches, you usually just jumper across it so it looks like a solid wire to the control.  Do this only when the unit is trying to fire up, so it is in the correct sequence. ~~ If you get no continuity however, it sounds like the contacts in the switch are shot and the switch should be replaced. Jumpering across it will let you know if that is what's keeping the heater from firing up. Do NOT leave the jumper in place as you're disabling a safety device." Source
"Because one of the two air chambers is vented to the atmosphere, the ambient (in the surrounding area) air pressure is critical. Ambient air pressure can push or pull on the diaphragm through the vent port. If the ambient air pressure is extremely high (positive) or low (negative) it may cause erratic pressure switch operation."

Pressure switches fail when a few drops of water condense in the small tube the connects to the switch, or some other internal problem with contacts happens.  Using a volt meter on the switch while gently blowing /sucking on the tube will confirm it's operation... or lack of operation.
Pressure switch troubleshoot
Intellivent pressure switch troubleshoot and testing
Test pressure switch
Air pressure switch testing
Intellivent wiring
Pressure switch replacement
Bradford White pressure switch replacement
Check pressure switch
Construction, operation, and testing for pressure switch .pdf

The Vacuum line can be clogged
Check pressure switch and vacuum line
"How to check the vacuum line
Requires the use of a magnahelic gauge.
1. Place inline “T” fitting between vacuum switch and vacuum line from the blower motor.
2. Turn heater on and adjust so water heater turns on. Blower motor turns on..
3. Check  pressure on the magnahelic gauge. If gauge shows 0.6 to 1.5 inches water column, then blower motor is inducing the proper draft and vacuum lines are not obstructed.
4. If gauge does not read between 0.6 and 1.5 inches water column -
a. Move the inline “T” fitting and place it between the blower motor and the vacuum tube at the top of the heater.
b. Check the pressure on the magnahelic gauge. If the gauge shows 0.6 and 1.5 inches water column, then the blower motor is inducing the proper draft and vacuum lines are obstructed. Replace the heater.
 c. If the gauge does not read between 0.6 and 1.5 inches water column, then the blower motor is not inducing the proper draft. Replace the blower motor."  Resource: Power vent troubleshoot / pdf
Buy: magnahelic gauge
water heater pressure switch Pressure switch/ Vacuum switch for water heaters
There are 3 major water heater manufacturers, AO Smith, Bradford White, Rheem, that make all the other brands from Kenmore, Craftmaster, Whirlpool, American, Reliant (AO Smith) to Reliance (Rheem)
Buy water heater pressure switch:
Rheem water heater pressure switch
Bradford White pressure switch
AO Smith pressure switch
Outlet polarity120 volt single-phase, Polarity, Ground
Power vent is connected to 120 (115-125) volt outlet. No electricity, no hot water. 5.2 FLA (full load amps) approximate.
Dedicated line recommended to reduce noise and surge on electric wire.
The outlet polarity must be correct, and water heater must be grounded.
Power vent heater is a polarity sensitive appliance and will not operate if the power supply polarity is reversed.
Poor ground can prevent flame. Water heater’s burner must be grounded for flame sensing current to be established and verify ignition.
GFCI circuit can cause short cycling. If outlet is not dedicated or has GFCI, or line has other loads such as florescent lighting, these factors can cause short cycling.
Unplug cord. Test for continuity between ground prong on plug and manifold tube on gas valve.
Test for continuity between ground prong and blower assembly mounting screw.
Connect water heater to different outlet. Test outlet polarity with circuit analyzer
Buy:
Circuit analyzer

Power vent circuitIntellivent gas control circuit
Vent temperature limit switch monitors the flue gas temperature in blower assembly. If temperature exceeds set point, the limit switch opens and turns off circuit that is routed from gas control valve through the limit switch and pressure switch. This signals to gas control valve to shut down gas flow to burner and water heater stops heating water.

Defective vent temperature limit switch; this is a normally closed switch that opens its contacts on a rise in temperature. Turn off power and disconnect wires to the vent temperature switch.

With the switch at room temperature (77 °F), check for continuity between the two wiring terminals on switch with an ohm meter. If switch contacts are open (no continuity) at room, or below 160°F - replace the switch.

power vent flue restrictorAt top of heater is a flue restrictor plate that is located on vent pipe under the power vent assembly. If restrictor is missing or dislodged, the flow of combustion gas will increase causing more hot gas to reach limit switch. If heat exceeds 160°F limit, the limit switch opens and burner shuts down.

Missing flue baffle can create turbulence inside combustion chamber, that can sweep gas away from burner causing ignition failure, and short cycling where water heater turns off for a few moments and then cycles on again several times before shutting down.
Turbulence can also be caused by improper or missing seal around combustion chamber access door

Resources:
Intellivent wiring
Read about replacing rubber seal
Minimum distance of vent pipe from window   
Larger image with more information
Minimum distance of vent pipe from window
Side-wall vent pipe must be 4 feet away from windows and doors. And 3 feet away from inside corners.


Consult product manual and local codes for specific vent installation.

Power direct-vent clearances
Venting a gas water heater
Conditions where outdoor air supply is needed
Condensation:
Formation of condensation in the venting system of Power Vented water heaters is dependent upon installation conditions including, but not limited to:
ambient temperature and humidity of installation location;
ambient temperature and humidity of venting space;
vent distance and slope; and product usage.in order to effectively control condensate from adversely affecting the mechanical components of the water heater several methods may be employed:
1. For horizontal installations the vent pipe can be installed with a downward slope (not less than 1/8 inches (3 cm)) and away from the blower.
2. In order to prevent condensate from draining back into the blower (vertical or horizontal runs), an optional condensate kit is available as a service part (Condensate kit, p/n 238-45875-00). A factory supplied exhaust adapter with drain outlet mounts directly to the blower outlet and is secured with two hose clamps, one to the blower and the other to the vent pipe. Tubing is provided to drain any accumulated condensate away from the water heater and to a suitable drain. The kit comes with instructions for installation.
Water leak?
A. Water at the blower assembly is water vapor that condensed out of combustion products ... caused by a problem in the vent.
B. Condensation  on pipes in humid weather or pipe connections may be leaking.
C. Anode rod fitting may be leaking (anode is located under the Blower Assembly). Replace anode rode
D. Small amounts of water from temperature-pressure relief valve, possibly caused by thermal expansion or high water pressure. Gently lift and then lower release handle.
E. TP valve leaking at the tank fitting, could indicate rusted tank. Re-install with 6+ wraps teflon tape. How to troubleshoot and replace TP valve
F. Water from a drain valve may be due to the valve being slightly opened. Install hose cap.
G. Drain valve leaking at tank, could indicate rusted tank. Re-install with 6+ wraps teflon tape. How to replace drain valve
H. Combustion products contain water vapor that will condense on cooler surfaces. Drop can drip onto the burner or run on the floor. This is common at start-up and when incoming water is cold.
I. Water in the water heater bottom or on the floor can be caused by condensation, loose connections, or TP valve. Inspection all possible water sources.
Leaking water heater
Steve writes about short cycling:
When my power vent is turned on, the Intelli-Vent activates & the burner ignites normally it burns for about 5 min & stops. After a few ignite attempts, the green led and A & B Yellow leds light up. Problem sticker states “max no. of ignites have been reached & system is in blackout.” This has been ongoing for a few weeks.
Is the vent pipe partially blocked... so the exhaust doesn’t vent properly & the burner is turned off?
Any suggestions to fix it?

Answer for error with A and B light / ignition failure or short-cycling
-Unplug heater to reset gas control valve.

-Low gas pressure can cause . 
-Observe operation of other gas appliances when heater is working. Low gas pressure should affect all appliances.
-Water in gas line and clogging can reduce gas pressure at individual appliance including water heater. Use only black pipe or yellow approved flexible gas line. Galvanized pipe will flake off pieces that can enter gas valve. Connect pipes so no joint compound or teflon tape can get into gas line and enter gas control valve. Install 3" sediment trap on gas line.
-Undersized gas line to heater can affect flow of gas. Check installation manual and BTU rating of heater. In some cases a full 3/4" (or 1") gas line should be run within so many feet of heater before reducing to 1/2" (or 3/4)
-Improper size yellow flex line can constrict gas flow. Check back of package to see BTU rating for each diameter of flex and compare with BTU rating of heater. Use black pipe connection directly to heater instead of flex line.

-Low voltage on 120 volt outlet.
-Min 115, max 125.
-Use dedicated outlet with correct polarity with no other inductive loads or interference on the line.

-Hot surface igniter
-Igniter wears out over time. Measure ohms  If multimeter shows 18.8 ohm resistance at room temperature, then replace ignitor
-If igniter or ceramic is cracked or damaged, replace igniter
-If igniter resistance is than less than 15.5. replace igniter
-If resistance is within range, and igniter is not damaged, then gently clean with very fine steel wool or very fine sandpaper. Do not touch. Oil from fingers can cause damage when igniter is hot.

-Misaligned igniter.
-Just as pilot light keep burner going, the igniter must remain hot throughout the heating cycle to ensure gas flame burns continually.
-If igniter is not sitting in the flow of gas, the heater can 'misfire' and start short cycling.
-Igniter must sit directly in front of a gas port on the burner and be correct distance away.

-Improper vent
-Check installation manual to ensure correct size vent. Vent diameter that is too large or small can cause short cycling.
-Do not exceed maximum overall length, horizontal runs, or number of elbows.
-If heater worked before, then vent installation is probably correct. Check for obstruction at vent termination. Inadequate venting would cause gas to burn lazy yellow color instead of crisp blue with flicks of yellow and red.

-Inadequate air supply... use correct size vent shows in the installation manual, check air intake, get more air to unit ... except if short cycling was caused by lack of air, then it would restart pretty quick when air was naturally replenished during shut down ... and flame would be yellow instead of crisp blue when turned on.

Other causes might include following:
-Rubber pressure tube/ vacuum line clogged or kinked.... check tube ... except why would it start running at all?
-Faulty pressure switch.... replace pressure switch
-Loose or dirty wire connections.... pull off and clean.
-Blower motor overheating, getting hot and slowing down ... replace blower motor

-Dirty combustion parts, faulty flame sensor, bad alignment of flame sensor ... clean burner, manifold tube etc.
-Bad or dirty flame sensor. Remember the flame sensor must operate continuously to keep ignition going since the unit does not have pilot light.
-Faulty or failing gas control valve.

-Overheating... the vent temperature reaches 180 degree F,  thermal switch trips off the blower. Put hand near vent to heel approximate temp, or use a thermal heat gun to measure. This indicates faulty intellivent gas control valve thermostat.

Flame sensor
-When gas is ignited ... if the flame sensor is correctly positioned, and not dirty (If  the flame sensor's metal is off color then change it out, or lightly clean with an abrasive cloth), then flame sensor confirms that flame is present and signals the gas valve to continue releasing gas.
Flame sensor for Honeywell power vent
Flame rod sensor
Location of flame sensor and igniter vary by model and brand of water heater.
Sand carbon deposits off igniter.
Avoid touching igniter
Larger image
Hot surface igniter troubleshoot
Hot surface ignition basics
Troubleshoot hot surface ignition
Hot surface igniter troubleshoot
Power vent hot surface ignition

Tip of flame sensor must be directly in front of burner port.
Use a nickel to set 7/64 gap.
Natural gas flame sensor will be bent, while propane will be straight.
Larger image
Intellivent troubleshoot Manual
Power vent surface ignition
Flame sensor for Intellivent power vent

The lower lip or edge of low NOx burner extends out further than standard burner. Flame sensor gap and elevation are measured from lower lip on low NOx burners .... and from top lip on standard burners.
Specifications here are for standard recovery residential power vent and power direct vent 40 and 50 gallon models.
Flame sensor chart
Power ventVenting for power vent models
Read product manual for venting specifications
Use correct size vent that shows in the installation manual. Too large or too small and the power vent can malfunction.
Example power vent manual p17
Minimum vent distance from window
Power vent tables
Power vent troubleshoot
Typical power vent manual
Typical power vent manual2
Typical service manual
Bradford White power vent service manual
Gas venting specs
Conditions where outdoor air supply is needed
Venting multiple heaters
Soot on gas burner
Soot on top of heater also implies danger of improper vent and backdraft.
Improper location of vent on roof, and incorrect clearances, or windy location can stop vent gas from leaving vent pipe. If vent gas cannot escape at top of pipe, it can be entering house at the vent hood. Soot on top of heater is evidence. If pilot goes out, the improper draft can be blowing out pilot light.
Soot on top of heater can be caused by backdraft where vent gasses are being blown back onto water heater because of shared vent pipe with furnace or other gas appliance. Read next section.
Negative inside air pressure, Negative pressure
Backdraft Is your furnace causing water heater to malfunction? Furnace, kitchen-bath bent fans etc can affect vent draft on water heater. Called negative pressure.
Is there evidence of rusting etc on top of heater, next to the draft hood? Is the furnace room particularly cold or wet? This is evidence of backdraft.
Here is a simple, but telling test. When the water heater first fires up, a little heat will spill from the draft hood. It should only spill for a second or two under normal circumstances. So, with the furnace off, turn the temperature on your heater up to cause it to fire up (you might make a mark on the thermostat dial so it can be put back to the same place). Quickly, put the back of your hand to the draft hood to feel any heat spilling out. Count the seconds. Return the heater to normal. Now wait a bit and fire up the furnace. Feel for any spillage at the water heater draft hood with the water heater off. Count seconds. Now fire up the water heater (furnace running) and check for spillage again.
If furnace and water heater both vent into same chimney, the draft might not work properly. Water heater should have dedicated vent. For example the chimney vent pipe is is eight inch, but the two vents (from furnace and water heater) going to it are both four inch. That bigger vent might be oversized and hard to warm properly for good drafting.
If the furnace is power vent, and fan or vent will overpower natural draft. Having the furnace and water heater vents combined will cause problems. Likely the
right fix is to run two, separate three inch vents. Resource: Venting combustion byproduct .... issues: vent in disrepair, other vents in house drawing air
Water on top of heater. Rusted vent pipe. White condensate on pipes.
Inadequate draft, or improperly installed vent pipe can cause condensation inside pipe that will rust and cause white condensate.
Missing roof cap will cause water on top of heater that will rust out the water heater.

Elbows slow venting, can cause backdraft if vent pipe is not large enough, or serves too many gas appliances..
Resources:
Gas venting specs
Direct vent clearances
Conditions where outdoor vent is required
 
Vent Gas Odor
Lack of air supply
  -Clean air intake screen, open window
  Ventilating tight-house/ pdf
Improper vent
  -Read product manual for vent requirement
Downdraft
Poor combustion
  -Clean combustion parts, service unit
CO poisoning
If joints fall apart, or vent is improperly installed, hot gases enter home posing risk of odorless CO poisoning. Symptoms: headache that goes away when outside in fresh air. Unconsciousness.
Remove affected people from home and lay on sides, not on back. Call emergency help.
call plumber. Attach vent pipe sections with 3 screws and then cover joints with aluminum tape.
Buy:

Vent tape
Carbon monoxide detector
Water leak issues
A. Water at the blower assembly is water vapor which has condensed out of the combustion products.  This is caused by a problem in the vent.
B.  Condensation may be seen on pipes in humid weather or pipe connections may be leaking.
C.  The anode rod fitting may be leaking (anode is located under the Blower Assembly).
D.  Small  amounts  of  water  from  temperature-pressure  relief  valve may be due to thermal expansion or high water pressure in your area.
E.  The temperature-pressure relief valve may be leaking at the tank fitting.
F.  Water from a drain valve may be due to the valve being slightly opened.
G.  The drain valve may be leaking at the tank fitting.
H.  Combustion products contain water vapor which can condense on the cooler surfaces of the tank.  Droplets form and drip onto the burner or run on the floor. This is common at the time of start-up after installation and when incoming water is cold.
Water inside bottom of combustion chamber or on the floor may be from condensation & loose connections, or the relief valve. DO NOT replace the water heater until a full inspection of all possible water sources is made and necessary corrective steps taken.

Resources: Power vent troubleshoot/ pdf
Bradford White power vent service manual


For power vent models
Range Low 90° - very hot 160°
Average bath 110°F, typical water heater temp 120°
ECO limit 199° F, ECO trips, gas valve fails
Average bath 110°F
ECO limit 199° F
TP release water at 170°
Buy
Example Honeywell gas control valve at Amazon
Reliance NG at Amazon
Replacement instructions
How to replace water heater gas valve

Resources:
Adjust temperature/ error codes on Honeywell
How to light Honeywell gas valve
Dampered Fury gas troubleshooting codes
Induced draft troubleshoot codes
Error codes, troubleshoot for gas valve
Error codes
Error codes2
Error codes
Bradford White power vent service manual 1
Bradford White power-vent service manual 2
Bradford power-direct-vent service manual
Condensing power vent service manual
Test gas control/ from BW service manual
Sequence of operation
How to clean burner

Safety
Water heater safety precautions
Water heater precautions/ pdf
Gas-water-heater-Safety-Precautions
Gas valve safety
Thermal expansion
Insulation blanket


For power vent models Range Low 80° to Hot 150° Error C flashes at 160°

Buy
Buy Intellivent gas control at Amazon
White Rodgers/ Rheem Intellivent gas control
AO Smith intellivent
AO Smith Intellivent at Amazon
AO Smith White Rodgers at Amazon

Replacement instructions
How to replace water heater gas valve

Resources:
AO Smith Intellivent troubleshoot and FVIR test/ pdf
Error codes and adjust temp on Intelli-vent gas valve
How to light water heater
Troubleshoot Intellivent/ pdf
FVIR intellivent troubleshoot .pdf
Intellivent service manual
Intellivent FVIR troubleshoot and reset
Sample manual
Intellivent wiring
Power direct vent troubleshoot
Sequence of operation
Intellivent error codes-troubleshoot
Promax gas water heater manual
For resetting controller: After the unit has been off for at least a minute, plug it in, turn on the switch; within a few seconds, depress both arrow buttons on the controller, and hold them until the left light begins to blink.  Release them, and within a few seconds, push those arrow buttons in the following sequence:  L/R/L/L/R/L/R/R.  This should reset the controller.
gas valve setting
Larger image
Buy
Gas control valve thermostats at Amazon
Gas water heater thermostats at Amazon
Rheem gas control valve at Amazon
Gas control valve at Amazon
Camco White Rodgers at Amazon
Gas water heater timer fits this valve
Replacement instructions
How to replace water heater gas valve
Resources
Service manual
Service manual 2
Service manual 3
Operation and safety
How to light water heater/pdf
General troubleshoot manual /pdf
White Rodgers gas control valve replacement pdf
Power vent water heater issues
Magnet testing
Test thermocouple
Gas valve testing
How to light gas water heater
White Rodgers NG replace, install, set temp


Robert Shaw 120Volt input gas control valve Wiper Control and Gas Valve assembly Triangle pointed upward is 120 degrees F Replacement for Rheem power vent/
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Rheem wiper SP20123A thermostat KIT
Wiper SP20123B valve/ no thermostat


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Error Codes and troubleshoot
Guardian power vent Robert Shaw error code
Check the blower motor, gas control etc
Rheem parts list
American power flex parts
General manual with lighting instructions
Replace water heater gas control and FV
Check pressure switch, blower, gas control
Sequence of operation
How to light water heater
To reset: turn the red control knob on and off 6 times within 30 seconds to reset the board.
White Rogers thermostat

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Troubleshooting/ pdf
How to light gas water heater
How to replace water heater gas valve


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Robert Shaw natural gas
Robert Shaw propane gas
Replacement instructions
How to replace water heater gas valve
Resources:
Robert Shaw models
Robert Shaw/ Unitrol troubleshooting/ pdf
General troubleshoot/ pdf
General troubleshoot manual /pdf
How to light water heater/pdf
Magnet testing
Test thermocouple
Gas valve testing
Operation and safety
Recalibrate gas control/ pdf
How to light gas water heater
Adjust pilot on unitrol gas control valve
How to test White Rodgers gas valve p14
How to test Honeywell Icon gas valve p23
How to test Robertshaw gas valve p14
14 things needed for gas water heater & .pdf resources
What you need for operation of gas water heater.
General troubleshoot
1) Basic parts and operation
2) Adequate incoming air supply ... issues: closed doors, tightly insulated house, very hot attic.
3) Adequate air supply getting to burner... issues: dirty vent screen, dirty environment, maintenance.
4) Thermal cutoff  ... TCO ... issues: failed part, maintenance, vent.

5) Flammable vapor lockout .... issues: exposure to vapors, bad FV sensor, failed FV system,
6) Fuel supply to gas valve thermostat ... natural gas and propane are different ... issues: wrong gas, low pressure, moisture in pipe, undersized gas meter, supply line too small for BTU rating.
7) Gas valve thermostat regulates fuel supply ... issues: not enough gas, failed thermostat, failed gas control valve.

8) Fuel supply from thermostat to burner ... issues: maintenance, thermocouple-thermopile, gas control valve.
9) Clean and replace burner ... issue: periodic maintenance requires burner inspection, cleaning, and possible replacement

10) Functioning thermopile-thermocouple-pilot light ... issues: misalignment, failure of part.
11) Ignition of fuel supply by pilot light or hot surface igniter ... issues: pilot light, piezo igniter, electrode.

12) Power vent water heater troubleshoot ... issues: pressure switch, blower, blower sequence from gas control, outlet polarity
13) Venting combustion byproduct .... issues: vent in disrepair, other vents in house drawing air

14) Misc troubleshoot manuals
gas water heater timer Gas water heater timer
Fits Honeywell, White Rodgers, Robert Shaw
Both Propane and Natural gas models

Resource:
Gas water heater timer
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Icon gas valve

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