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Test and repair Crossover/ Cross connection

Tankless flow rates

Crossover: when cold water gets into hot pipe

Or hot water gets into cold pipe.

Hot water never shows up.
Hot water not very hot.
Hot turns cold and then hot.
Cold water seems warm or hot.

Tankless: Crossover can cause tankless water heater not to activate. Read: No error code on tankless.
Plus read information below.
Crossover can affect tank and tankless water heater.
Can affect under counter water heater
Test temperature

1) Check tank for hot water

1) For tank-type and tankless, put bucket under overflow tube and gently raise and then lower TP lever.  If water is hot at TP valve, but no hot water arrives at tap, then that indicates crossover issue. Read more below for locating problem.

Keep feet, face, hands, kids, and pets away from hot water that will blast out of TP overflow tube.
Apply cold water immediately to any burned area of skin. This action will reduce severity burns.
Raise TP lever
Raise TP lever to see if tank has hot water
2) If water is putting off steam, then water is hot. Or use cooking thermometer to measure water temperature and compare with thermostat setting to get base line.

3) If water heater temperature is set too low, then adjust temperature: How to adjust water heater temperature

4) If tankless computer thermostat is set too high, and incoming water is too cold, then unit will not activate.

5) If thermostat set to 150, and water is 100, then problem is at tank, or tankless.
220 degree Instant-Read pocket thermometer
140 degree thermometer at Amazon
Thermometers at Amazon
How to troubleshoot electric water heater
How to troubleshoot gas water heater

2) Check for Leak

Water heater cannot keep up, so water seems cold at faucet.
Turn off all taps, and put ear against pipe to listen for leak.

-Broken pipe. Turn off all taps and put ear against pipe.
-Dripping and leaking faucets can consume hot. Fix leaks.
-Leaking TP valve. Replace TP

3) Check for Broken dip tube on tank-type

Cold water enters top of tank instead of bottom
Read: dip tube
Bradford White mixing valve
Larger image

Mixing valve
Larger image

4) Overview of Crossover causes: what to look for

1) Most common cause: single-handled faucet cartridge has gone bad.
Cold water enters hot line (or hot water can enter cold line).
Hot is slow to arrive or never arrives.

2) Faulty check valve on recirculation system. Check valve allows water to flow one direction, and then stops water flow going other direction. Action: Dis-assemble cross piece on recirculation and clean with white vinegar.
Recirculation system

3) Faulty check valve in plumbing system. Action: replace check valve. Make sure check valve is installed horizontally and not vertically
Check valve can also cause closed pressure system and cause TP valve to release water, and cause frequent TP valve failure.
How to test and replace TP valve   Repair water heater valves

4) Reverse Osmosis system, where hot and cold lines cross connect with each other.
Action: disconnect system temporarily.

5) Faulty Mixing valve can be installed in-line, or installed on top of tank.
How to save hot water using mixing valve
Mixing valve is used on some water heater systems so washing machine receives very hot water, while lower temperatures are delivered to kid’s bathroom.
One method that mixing valve creates lower temperatures is letting cold water enter the hot line.
When mixing valve goes bad, it can let larger or uneven amounts of cold water into the hot line so that hot never arrives at faucet, or temperatures are unpredictable.
Action: Replace mixing valve.

Note: Temperature setting over 140 degrees can distill minerals out of water that can clog mixing valve, recirculation system, pipes, inlets, etc.
Reduce temperature below 130 degrees to save money. How to adjust water heater temperature
Crossover valve
Replacement crossover valve
watts recirculation systems

4a) Bad crossover valve on recirculation system

If home has recirculation system, and cold water or hot water never arrives at faucet, then crossover valve should be replaced.
Replacement crossover valve
Water heater recirculation installation, troubleshoot, manuals

5) How to test for crossover at faucet(s)

1) Turn off hot water at tank –or- at tankless unit.
This is done by using the shut-off located above water heater.

2) Turn ON all faucets on HOT side.
3) Wait 5 minutes.
4) If any water is flowing, then you have crossover problem.

6) Locate faucet with crossover problem

IF water is running at one or more faucets, then water is entering hot pipes from 1 or more locations.
Following test shows how to narrow down suspects.

1) Best suspect is the faucet(s) that ran during test. BUT this faucet may not be the problem.

2) Turn OFF all faucets except one faucet open on hot side.
One faucet is turned on Hot, and all other faucets are off, and hot water at tank is still turned OFF.

3) Go to each faucet in house. Put ear against each faucet and listen for flowing water.
4) When you hear water flowing, then that is the faucet with crossover problem.

5) Also put ear against check valves and recirculation pumps to help locate source of problem.
There may be multiple crossover issues, and the combination is causing the problem, so check everything.

6) Action: Replace faucet cartridge or check valve to solve problem.


Stacking can be caused by crossover
Stacking is when several short draws of hot water cause cold water to enter tank.
Tank is already up to temperature.
Several short draws activate thermostat, and more heat is applied.
Temperature at top of tank gets hotter than usual.
Hot water slow to arrive at faucet
Larger image

Typical faucet has 2 gpm (gallon per minute)

Typical tub spout has 2-1/2 gpm

2 gpm means faucet can fill one gallon container in 30 seconds.

2gpm water flow= in 30 seconds hot water will travel a distance of 83' along 1/2 pipe.
Water heater formulas and terminology/ pdf

If single handle faucet is lifted in center, then equal amounts of hot and cold water will flow, so distance is halved along each 1/2 pipe.
Low hot water pressure
Flow rate of 2 gpm through the water heater is a flow rate of 17.43 inches/second through a 3/4 inch ID pipe Read
water flow rate
30 seconds

Hot water slow to arrive at faucet

1) Use timer and 1 gallon container to see how many gallons of water come out of faucet in 30 seconds.
2) Measure distance from water heater to faucet.
3) Open hot water faucet. Use timer and see how long it takes hot water to arrive at faucet
4) Measure water pipe diameter. Most pipes from water heater are mixed 3/4" & 1/2"
5) Use chart above to see if hot water is slow to arrive at faucet.
See chart: How far does hot water travel in pipe in 30 seconds

How long does it take to fill 1 gallon jug

10 seconds = 6 gallon per minute
15 seconds = 4 gallon per minute
20 seconds = 30 gallon per minute
30 seconds = 2 gallon per minute
Additional links

Other tips for saving money:
9 ways to save with water heater

1) Do not turn on hot tap when using cold water.
Each time hot is turned on, even for a moment, cold water immediately enters water heater. Water heater runs more.
This problem is more likely to affect tank-type water heater than tankless, since tankless require minimum water flow before heating is activated.

2) Single handled faucet that is lifted in center will draw hot water from tank.
Always lift single handled faucet over onto cold side when using just cold water

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