Question about Bosch AquaStar 125FXKIT-NG 125FX Natural Gas Tankless Water Heater w/ Hood

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On demand water heater won't stay lit

Replaced the thermocoupler, the issue seemed to improve, now the pilot needs to be relit up to 4x a day.

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My tankless water heater is 4 years old. The pilot light will ignite the gas. However the fire goes out almost imediately and tries to re-ignite. Seams to have been gradullay getting worse.

Posted on Sep 03, 2009

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It's the gas valve. This pretty common. The thermocouple produces a small amount of current from the heat and this current holds the safety valve open inside the gas valve. Sometimes the safety valve gets sticky and your symptoms describe it exactly. People are always frustrated by the time it is certain to be the valve. You need to replace the valve. No one is allowed to fix a gas valve - liability - gas etc. Replace the gas valve and your problem will be solved. I am a master plumber/gasfitter and I am confident that this will solve the problem. Been there - done that.

Posted on Jun 17, 2009

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1 Answer

Reliant 501 Natural Gas won't stay lit


Reliance water heater?
Thermocouple is good if the pilot stays lit continuously.

501 is older model. Unknown if this unit has FVIR protection and sealed combustion chamber or open air intake on front of unit.
http://waterheatertimer.org/pdf/Reliance-2006-Service-Handbook.pdf

With FVIR protection:
Get more fresh air to the unit.
Clean the flame arrestor screen.
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http://waterheatertimer.org/How-to-test-water-heater-thermocouple.html
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If pilot lights and flame is robust and clear blue, and pilot goes out later, then some suspects can be excluded: air in gas line, low gas pressure, thermocouple is overtightened (finger-tight + 1/4 turn), thermocouple not positioned correctly in the flame, dirty pilot tube.
If flame is yellowish and small: then clean pilot tube and combustion parts.
http://waterheatertimer.org/How-to-install-gas-water-heater.html#clean
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Open following links to read troubleshoot resources.
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
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Richmond power vent will not stay lit, the bunrer will lit than after about 5-10 min. it goes and tries to relite and than goes into lock down. after it about 5 min. you can reset it and it will do the...


Richmond-Ruud-Rheem
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf

It sounds like you've read the manual.
And cleaned the burner parts according to manual.
You replaced thermal reset, but system is still tripping, so either the gas valve and tubing are bad, the thermocouple is bad, or there is a problem with gas pressure, or gas line.

Post question on pro water heater forum:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

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Pilot light will not stay lit


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Pilot light won't stay lit after release of gas valve.tried few t


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Here is a site with basic information to get you going.

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