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 Fuel supply from thermostat to burner

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Gas water heater burner
Larger image natural gas burner
Another images
NG gas burners are different than LP burners.
Connections to natural gas control valve are right handed.
Back to 14 things for troubleshooting water heater
7) troubleshoot fuel supply from thermostat to burner
The gas control valve lets gas flow into the combustion chamber through the pilot tube and manifold tube.
The pilot tube has an orifice that restricts gas flow for the type of gas and the amount of pilot flame needed.
The manifold tube is larger and sends gas to the burner in the amount to meet BTU rating of water heater.
The gas control valve must match the pilot and burner. 
Propane gas burner
Propane gas burner made of cast iron, shows manifold and pilot tubes, and thermocouple. Connections to gas control valve are left handed.
LP has more pressure and higher temp
Check gas pressure on water heater:

1) Quick assessment of gas pressure
Watch what appliances do when adding load. If appliances stop working correctly when another gas appliance is activated, it implies low gas pressure. This observation can be done without equipment.

2) Supply gas pressure
Supply gas pressure, or line pressure checks are measured before the gas control valve and as close to the water heater as possible.
"The minimum permissible gas supply pressure for the purpose of incoming gas supply to water heater is 1.0" water column (.25kPa) above the operating manifold pressure. See the rating plate and combination gas control for the manifold pressure and gas type. The maximum permissible gas supply pressure is 14.0" water column (3.5kPa) for natural gas and liquefied petroleum gases/propane gas.
"The Gas Control is designed for a maximum line pressure of 14.0" w.c. and a minimum line pressure of 1.0" w.c. over the water heater’s rated manifold pressure.
Line pressure must be checked with the main burner on and off to assure proper readings."
If line pressure is low: increase gas pressure regulator, or call gas company.
If line pressure is high, add gas pressure regulator, or call gas company.

Pressure rating is shown on water heater label
Check rating plate (label) located on side of water heater  for gas pressure rating
Typically, a propane heater will be higher than natural gas.
Line pressure is pressure on incoming gas line. Label shows max inlet or line pressure as 14.0" w.c.
Manifold pressure is gas pressure from gas control valve to burner. Label shows 4.0" w.c. to 5.0" w.c. for manifold pressure.

If the burner and/or pilot do not function, service checks for gas pressure, thermocouple output, magnet assembly and ECO are to be performed. If these check OK, the gas valve may be faulty."
Resource:
How to check gas pressure on water heater
Clean burner
Back to 14 things for troubleshooting water heater
ao smith burner assembly
Image shows natural gas burner assembly with piezo igniter, pilot tube, manifold tube, and thermocouple.
Some gas water heaters have modular burner assembly that is replaced whole, instead of individual parts.
Buy:
AO Smith burner assembly
Rheem burner assembly
Bradford White burner

Clean water heater burner line
Expanded image
Burners and burner assemblies can be cleaned serviced.
-Maintenance manuals suggest annually cleaning burner area with wire brush and vacuum cleaner.
Buy:
Tube cleaners at Amazon
Burner brush

Burner brush
Buy:
Tube cleaners at Amazon
Burner brush tube cleaner at Amazon
Burner Tube Brush Cleaners at Amazon
Appliance cleaning brushes at Amazon
Straw cleaning brush
Soot on gas burner
Soot implies unburned gas: dangerous situation
Gas may not be burning fully: lazy yellow flame indicates poor incoming air supply, dirty combustion parts, inadequate venting of combustion byproduct.


Soot on gas burner
Soot on top of heater implies danger of improper vent and backdraft #11 venting
Improper vent can blow out pilot light.

Flame should burn clear blue
Low gas pressure.
Dirty combustion parts.
Poor incoming air supply.
Inadequate venting. Clean thre flue

This is dangerous because unburned gas can accumulate inside combustion chamber or inside the flue way. Causing ignition.
This situation will overheat combustion chamber and trip ECO, TCO and FV system, causing water heater to stop working.
Clean water heater burner
Use wire brush to clean burner assembly and combustion chamber. When re-starting cold tank, expect possible condensation dripping until tank reaches temperature.
This is the only time water should be apparent inside the combustion area of water heater, otherwise #11 bad vent or leaking water heater is suspect.
Cleaning water heater
Burner cleaning /pdf
Example: how to clean combustion chamber
Example: cleaning combustion chamber
Example: how to clean combustion chamber
Clean sediment out of water heater
Clean combustion chamber Effex water heater
Leaking water heater

Look upward, and to one side, through sight glass to see that pilot flame is lit and clear blue color.
Causes for pilot outage:
Backdraft from shared vent and wind coming down the flue can blow out the pilot. see section 11 for venting. Dirty combustion parts and need for maintenance can also cause outage. see section 7. Bad thermopile or thermocouple. Misaligned thermocouple can also cause outage. Modern water heaters have solved the misalignment problem with fixed positioning and 1-piece replacement for combustion parts. see section 7. Bad gas control valve can cause pilot outage. see section 6.
Pilot light troubleshoot:
Clean the air intake, and get more fresh air to unit.
 Push in TCO located on front of combustion chamber.
Pilot troubleshoot resources
Test thermocouple
How to light gas water heater
Pilot light goes out
Burner goes out when control knob turned to ON
Pilot light will not stay lit/ pdf
Pilot outage/ pdf
Pilot problem or ECO or gas control?
Wind blows out pilot light
Pilot light or thermocouple?
Negative pressure blows out pilot
Pilot orifice
Pilot tube orifice
Clean with compressed air or carburetor cleaner
Do not rub with rag, or tube can clog

Buy
Tip cleaner

Pilot troubleshoot resources con't
Standing pilot light maintenance
Attic Ventilation and Pilot Outage
Pilot outage and negative pressure
Pilot light maintenance/ pdf
Ventilating tight-house/ pdf
Pilot light troubleshoot
Gas water heater partsWater heater giving off gas smell when operating: 
Check for gas leak. If no gas leak, clean the flue. Check for blockage of vent (snow over the roof vent).
The flue is located in center of water heater. The flue baffle sits inside the flue and is a twisted piece of metal that can be pulled up out of water heater. This requires space above heater in order to lift flue baffle completely out.
'Flue cleaning is dirty. Use a shop vac.  Turn gas control valve to pilot.  Remove draft hood and vent pipe.  Hose out the vent pipe outdoors.  Pull baffle up and out. Rotate it in the flue, bang it around to help clean off soot which falls down onto the burner.
Take baffel outside and hose it off.  Water is good for removing soot.  Vacuum out combustion chamber. Remove burner assembly and carefully hose out the burner assembly ABOVE the main orifice.  This will clean soot out of the burner, while keeping the rest dry. Other option is to vacuum the burner in place.  

If things go a certain way, you'll look like a coal miner when finished, but heater will burn with a nice blue flame. If it does not, gas pressure is the next thing to check.'
You can casually check gas pressure by observing other appliances when several appliances are in use.
How to check gas pressure
Rust and Condensation inside the water heater burner:
"Condensation is a mild acid – it will corrode steel
Condensation is usually noted when:
• water dripping is heard (only) while the main burner is on,
• there is “water” around the heater just after the heater has been operating,
• there are small, black or red granules on the main burner or top of the heater or
• corroded jacket or vent piping is noted. 

Flue gas products contain moisture. If these flue gas products are cooled to their “dew point”, they become visible moisture – condensation. Flue gas may become cooled by: • Cold supply air temperatures • Cool surfaces – generally, if tank water temperatures drop below 110°F, the flue pipe surface and/or bottom tank head will be cool enough to cause condensation. • Increased combustion efficiency – higher thermal efficiency means that an increased amount of heat is transferring from the flue gas into the water. If you transfer (approximately) 87.5%, or more, the moisture in the flue gas will condense."
Resources:
Replace thermocouple with Unitrol gas valve .pdf
Replace thermocouple .pdf

Test thermocouple I .pdf
Test thermocouple/ thermopile .pdf

Generic replacement steps for replacing burner .pdf
Cleaning the burner .pdf
Burner cleaning
How to clean combustion chamber .pdf
Remove combustion cover .pdf
Replace burner: Steps start here
Back to 14 things for troubleshooting water heater
Gas water heater burner assembly
Door and burner assembly are removed to replace thermocouple
Larger image
Whole assembly is replaced
Newer models 2009- current (depending on brand and model)
Typical 6-year tank has 6 years parts and tank, so the part is covered 6 years, labor covered year 1.
Contact manufacturer with model number, serial number, to find exact part number and warranty coverage.
Water heater manufacturers
Age of water heater

Generic steps for replacing burner parts
Burner access door gasket
Some brands require separate door gasket.
Should have gasket on-hand in case removing door causes gasket to tear.
Some models
Gasket may be needed
Generally, water heaters from Rheem, Ruud, Richmond, GE, etc might require separate door gasket. Remove carefully if gasket is reused.

Water heaters from AO-Smith, American, State, Reliance, Kenmore, Whirlpool might have one-piece door and gasket that is reusable

Read product manual to identify parts.
If you do not have manual, look at label on side of water heater to identify company     Water heater manufacturers
General location of Thermocouple
Note: end of Thermocouple must sit in the pilot flame.
Heat from pilot creates small current that travels to gas control valve, and keeps control valve open so gas will flow to pilot and burner. If thermocouple falls away from pilot flame, or flame goes out, the absence of electric current will turn off gas to pilot and burner.

This type thermocouple requires removal of burner from combustion chamber
Step 1: Turn off gas
Locate gas shut off.
Handle parallel with gas line => Gas ON
Handle perpendicular across gas line => Gas OFF

Rotate gas shut off handle perpendicular across line to shut gas OFF.
Step 2: Notes before starting
Note each tube connected on bottom of gas control.
Note how tight each is when removing, so re-installation is about same.
a) Thermocouple connection is finger tight plus 1/4 turn
b) Manifold tube carries gas to burner
c) Pilot tube carries gas to pilot light
Gas has less psi than water, and connections do not need to be as tight.
Do not overtighten.

These connections do not need pipe sealant or teflon tape.

For propane, manifold tube threads are reverse.
Natural gas, threads are regular.
Step 3: Remove screws
Remove screws holding door

AO-Smith, American, State, Reliance, Kenmore, Whirlpool have hex screw
Rheem, Ruud, Richmond, GE have tamper-proof screws.
Use punch to break out center, and hex to remove

Manifold tab fits into bracket
Step 4: Remove burner
Be careful
Do not dump debris off the burner where it can fall down onto arrestor screen
Burner will hook into a slot, or slide out from under a holder, or slide out of a slot.
Refer to product manual for illustration.
AO Smith-American-State-Reliance-Kenmore-Whirlpool manuals generally have clear instructions and illustrations.
Do not expect Rheem-Ruud-Richmond-GE manual to have illustrations or instructions.

Manifold tab fits into slot, or bracket

DO not dump debris off burner
   Prevent clogging Step 5: Carefully vacuum out combustion chamber
Keep stuff from falling down onto the air intake screen
Step 6: Get ready to replace
Take photos
Mark-n-measure where new thermocouple should fit
End of Thermocouple must sit in pilot flame 3/8"-1/2" to work correctly
Pilot assembly will be held in location with screws
Step 7: Replace
Remove thermocouple by slowly, firmly pulling and twisting from bracket
If thermocouple will not disengage from pilot assembly, then replace entire assembly

Removal from door might be easier by cutting copper tube with wire cutter
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame
There will be a grommet-type holder to keep thermocouple in place.
Replace thermocouple pdf

Image shows 3-legged water heater
This type water heater is easiest to clean without removing combustion parts.
Step 7: Clean the air intake before putting parts back
Rheem, Ruud, Richmond, GE air intake screen located below combustion parts.
AO Smith, American, State, Reliance, Craftmaster, Kenmore, Whirlpool the air intake screen located  bottom of heater.
Use compressed air. Use borescope, or mirror and flashlight to inspect.
Clogged air intake screen will cause overheating.
Move boxes, rags, etc away from water heater for improved air flow
Slow incoming air supply, causes slower venting, yet same amount of gas is burned.
Slow venting with same amount of BTU output will overheat combustion chamber, and trip FV system.
Each manufacturer has different steps for repairing FV overheat, depending on Brand, Age, Model, etc of water heater.

DO NOT USE HARD BRISTLED BRUSH ON ARRESTOR SCREEN
Use soft brush, paint brush, compressed air, vacuum cleaner.
LP and NG models vary
Rule of thumb is .125" [or thickness of nickel]
Igniter and pilot must be positioned closely so gas escaping the pilot orifice will flow into hot ignitor.
Once the pilot ignites, the tip of thermocouple or thermopile must be in the pilot flame.

Larger image
Step 8: Re-install burner
Reinstall burner. Wait to reattach door screws until tubes are connected.
Re-connect tubes to gas control valve before attaching combustion door screws.
Manifold tube on LP gas water heater is reverse thread.
Do not overtighten tubes. Remember how tight each connection was when removing.
Thermocouple is finger tight + 1/4 turn.
If thermocouple is overtightened, the electric current produced by thermocouple will short out against gas control valve, and gas control will shut off gas to burner and pilot. Can result in damage to parts and water heater will not function and pilot will not stay lit.

Reinstall combustion door screws, with gasket properly aligned, and sealed
Step 9: Turn on gas
Turn on gas to water heater
Check all connections for gas leak using soapy water.
Use chloride-free soap and water
Propane is heavier than air, so smell close to floor
Natural gas is lighter than air, so smell higher
Give leak time to show itself, since gas pressure is lower than water pressure
Step 10: Light heater
Light gas water heater using instructions printed on side of water heater.
Gas flame should be clear blue, with small amount of yellow and some red.
Step 10: More Options
A) Call service technician to fix water heater

B) Continue troubleshooting:
How to troubleshoot gas water heater
How to repair Rheem FVIR

C) Install new water heater
How to install gas water heater
Recycle old water heater
Pilot flame troubleshoot Troubleshoot pilot flame
Tip of thermocouple or thermopile is 3/8" to 1/2" into pilot flame

It may be hard to see pilot flame on some models
Sight glass location varies by model of water heater
People often do not get low enough to see pilot flame.
When viewing pilot flame, generally you must look upwards through sight glass and to the right.
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
15) How to install gas water heater
16) How to maintain water heater
Additional links
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