Water Heaters - Before replacing thermocouple?

Hello All

Came home tonight to find the pilot out on this 10 year old (9-26-94) Bradford White 40 gallon model. :eek: (Hey, that's what I actually look like!) Typical indication of bad thermocouple: the pilot re-lights until I let go of the red button after 60 secs +. Replacing the thermocouple seems easy enough (assuming I can find a place locally that has one). But before I proceed, I thought I'd ask a couple of questions:

1 - Is a 10-year-old unit too old to bother with? Using a flashlight to check the underside of the tank (above the burner), there is some rust near the sides, but not a lot. No sign of leaks.

2 - There's these little sensor devices up near the flue (Do they "sniff" for carbon monoxide or sense heat back draft?). My concern is that they have wires that lead into the little tube above where the thermocouple wire threads in. So, if these devices detect a problem or malfunction, will they shut off the pilot as well? If so, how can I diagnose whether the problem is with these sensors or with the thermocouple?

I see from other posts here that this no-pilot problem could be a couple of other things as well (spill switch - whatever that is? The control valve?). I guess the thermocouple seems like the place to start, but I thought I'd check here first.

Thanks for any advice.

Regards,
Anthony Giorgianni
Connecticut, USA

agiorgianni, Welcome to the DIY Forums.
The wires and sensors you saw ARE the spill switch. You are correct that they shut off the gas when they sense a problem. I would still replace the thermocouple first. Ten years is starting the downhill side of water heater life so you may want to start putting a little cash back for a new one.Good luck.

Hello Anthony and Welcome to our Do It Yourself Web Site.

The sensor at the top of the water heater senses heat. If flue fumes and gases are present, they will heatup the sensor and break the electrical connection between the thermocouple and the pilot. Thus extinguishing the pilot which in turn shuts the burner off.

Gases present means the fumes and gases are not going directly up the flue vent pipe. Some or all of the fumes and hot gases are backflowing and spilling out of the divertor and back into the room. The heat from the gases and fumes activates the sensor which turns off the burner to prevent fumes, gasses and potential carbon monoxides from entering the room.

The above should explain the operation and functioning of the sensor.

When a pilot flame will not remain on, chances are the thermocouple (TC) is burned out and needs to be replaced. I sugguest replacing the part as a first attempt to solve the problem. Chances are it will.

If you are included to run a simple test first, try this. Remove the wire disconnect from the sensor and try to relight the pilot. If pilot remains on, sensor is defective. If pilot will not or does not remain on, TC is defective.

Be sure to reconnect the sensor wires after or before replacing the existing TC with a new TC. Some, if not all, safety systems such as this type with flue vent sensor, will not allow burner operation or pilot to remain on with sensor wires disconnected, regardless of the operating condition of the TC. The system is total fail safe device and will not allow any pilot or burner operation, if the sensor wires are disconnected.

Thank you both for the great and quick responses.

Turns out, my landlord (I'm renting a condo) wants the gas company to come in and repair the unit even though I offered to do the thermocouple myself. I also wanted to be prepared to do it in case he was away traveling or something and couldn't be reached. But he insists on calling the gas company, which has promised to send someone tomorrow. I'll update this thread after the technician looks over the heater. I suspect it WILL be the thermocouple, but who knows.

Thank you both again. Great site, great advice. Now I actually look like this ;)

Regards.

Anthony Giorgianni

Connecticut, USA