I just moved into a house and when they turned on the gas they mentioned that the pilot light wouldn't stay lit. I suspected the thermocouple as I've had that problem before so I signed off and the next day I went down to Ace and bought a thermocouple. I installed it and it still wouldn't stay lit. :confused: So I went to Lowe's and got another one. I installed it and it still wouldn't stay lit. :confused:

I have no problems lighting the pilot. The flame is blue with a few yellow flecks from time to time. The thermocouple is new. And it still wouldn't stay lit.

So I replaced the Control valve with a new one. Tried all three thermocouples and the same problem occurs. :mad:

My heater upstairs works fine so I know the other appliances are getting gas.

The Pilot light seems to work fine.

Does anyone have any suggestions as to what to try next? Thanks.

Hi sendme...

A name brand, a model number and a serial number would really help here... ;) You can usually find these at a sticker located at the front center of the heater.

Get back to me...

MARK

Hi! Thanks for helping. Here's the info and the sticker:

Brand Name: Rheem
Serial No: RN 0795136734
Model No: 21V40-7N

20799

Thanks!

When you say you replaced "Control Valve" , do you mean the entire aluminum box into which gas line connects ?




Inside that box is a safety / automatic valve that opens and closes as it receives signal in milivolts from thermocoupling. It sounds like it is not opening all the way, meaning, it would be malfunctioning or perhaps even wrong thermocoupling.

If I am reading the sticker correctly, the manufacturing date is July 95, which would make it long past its warranty. However, contact Rheem customer support. They are on-line 24/7. Here is their link: http://www.justanswer.com/home-improvement/hvac/rheem?r=ppc|ga|2|HI+-+HVAC|Rheem&JCRN=Rheem+Technicians&JRA=2722239%3b2721303%3b2727414&JPKW=rheem+support&JPDC=S&JPST=&JPAD=2722771318&JPAF=txt&JPCD=20090212-1&JPRC=1&gclid=CJ6_iIHbipsCFRxNagodIRVNpQ .

Yes, I replaced the square box that the gas, thermocouple go into and the pilot light tube and burner tube come out of. The replacement was simple. No leaks in the gas connections or the connection to the tank.

I also tested the new box with both thermocouples with the same result.

I can light the pilot while pressing the button, but after lifting the button, the pilot always goes out.

I'll contact Rheem, but is there something else I can check for? I'm really stumped...

Please, come back to tell us what was wrong... We are learning with you. Thanks...

Okay, so the problem was indeed the switch. I decided to test the thermocouple by hooking it up to my multimeter. The thermocouple checked out, so I didn't know what to do. However, there was a pizeoelectric starter cable coming out from the gas control box (the old one didn't have a starter so it wasn't hooked to anything). The starter's wires were powered by the thermocouple and as a result, if they weren't wired into a starter, the thermocouple circuit was broken. By wiring the two wires together, the heater stayed on as expected. Got lots of hot water now!

20952
Checking the thermocouple. Notice the black and white wires coming out. Those had to be wired together for it all to work. The instructions sure didn't mention that! I paid the expert 20 bucks and it was worth it as it saved me several hundred in buying a new water heater.

Total cost:
New thermocouple - 10 bucks
New control box - 60 bucks
Expert answer - 20 bucks
Grand total - 90 bucks
Learning something new while fixing a water heater myself instead of hiring someone and paying a lot more? - priceless!