My pilot light won't stay lit on my gas hotwater tank. It is most likely the thermocouple because the pilot lights up while I am depressing the button but goes immediately when I release it. I turned the dial to off. How long can I have that set that way without the pilot light on? Will gas fill the air? Are we in danger? I can't get someone into to fix it for several days. Or should I leave the dial on PILOT until I can have it serviced?

You are in no danger. Gas will not flow unless the thermocouple senses the flame. If you are in doubt, just shut the gas supply off to the water heater.(there should be shut off within three feet of the water heater)

Take a piece of fine sandpaper and clean the thermocouple.

You have to hold the pilot button for 2-3 minutes at least after lighting the pilot.

It can stay on pilot or off forever. The pilot setting is sometimes called vacation and is used when you go on vacation.

Kiss, can you really clean a thermocouple? Ive never heard of that(but then again, I've never heard of a lot of things), I was always told that either a thermocouple was good or bad. Really curiouse about the cleaning of a thermocouple. Completely different than a flame senser, which I know can be cleaned.

They probably shouldn't even be called a thermocouple. They are probably thermopiles. Thermopile - Wikipedia, the free encyclopedia

Thermocouples are generally used to measure temperature but doesn't generate any power.

Even Wikipedia says it's a thermopile. Thermocouple - Wikipedia, the free encyclopedia

The better the thermal contact, the more voltage is generated.

As I said, it's not really a thermocouple, but rather a thermopile.

Here is a thermocouple table. http://www.omega.com/temperature/Z/pdf/z218-220.pdf

The voltages generated assume a reference junction of 32F. The old way was to use a series loop and break the loop and insert a high impedance voltmeter. You would then insert one of the junctions in an ice bath. Now the resultant measured voltage can be looked up in table to get a temperature.

The better the thermal contact with the flame, the more the generated voltage.

Yea, I know. You had to ask, didn't you?

Thank you very much for your help! I will shut the gas off then. Dealing with gas makes me nervous. I looked up instructions on how to replace it... but didn't see anything about sandpaper. I will try that, thanks! I couldn't find anything on the safety of the duration of having the dial turned to OFF and for how long. But this site came up. The Pilot setting is on a different dial than the vacation dial. It is on the top smaller dial that has ON, PILOT and OFF in between the pilot button and the igniter. The vacation option is on the dial just below in the front. It also has Warm or Hot. I have the top dial set at OFF and the temperature dial set at Vacation. Is this correct? You are both been very helpful. Thank you! :-)

That's fine.

You want the thermocouple smooth.

Thank you so much for you help! :-)
I will try and fix it myself tomorrow then.

I agree with Mygirlsdad (Lee) haven't heard of sanding the thermocouple, I would change it they are cheap and easy to replace.

When the pilot is off your gas valve is shut and no gas coming from the gas valve, when the pilot is let the heat from the pilot light will generate a current measuring 20 millivolts in the thermocouple circuit, This voltage is sufficient to control and hold in the "open" position the gas control supply valve to the pilot. The current will flow and the supply valve will remain open, allowing gas to flow as long as the flame is lit, but once the flame fails, the temperature drop, reduces the current required to open the valve and the gas supply is closed off, preventing excess gas buildup.

If you are in doubt, just shut the gas supply off to the water heater, Good luck.

John

Explain:

Quote:

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Originally Posted by afaroo

a current measuring 20 millivolts

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For the longest time, I thought the unit was named after André-Marie Ampère

See: Ampere - Wikipedia, the free encyclopedia

Yea, I know. You had to ask, didn't you?[/QUOTE]

Sorry I asked. By the time I got done reading through the sites you listed, I had forgotten what I had even asked, actually made me kind of tired, think I need a nap now, thanks a lot.. lol.

I'm sorry to disagree about the thermocouple lead , it does generate electricity in millivolts, you have to have so many millivolts to hold the magnetic head down in the control.That is what holds the main control open and the control then knows it has a flame to ignite the main burner when it is necessay.The thermocouple is either good or bad but also the pilot light could be dirty and not touching the thermocouple properly.For a easy try to fix clean the pilot and change the thermocouple lead, use a copper one and not an aluminum one, if the if the pilot light stays on and the main burner comes on then problem solved make sure you also turn your control to the proper temp that you wish. If the burner does not ignite after pilot stays lit or the pilot still will not stay lit call a service tech.

Thank you John. I was told that they cost only about $10.00. So I don't have to change it again soon, I will replace it with a new one. Thank you. At this point I think I will go buy the new one and have Atco come and fix it for free. I am worried about turning the gas off all together... don't want to break anyting and blow up the house. I will watch and learn for future reference. Thank you all! :-)

Thanks for the update, yes this is good idea that an expert replace it for you it is very simple just watch him and you learn it, Thanks.

Regards,
John

Ok, I think I am going to be brave. Outside on the meter it has a valve on the pipe that goes down into the ground. There is lever that is straight up with a hole in it the size of a time. About 1/4 the way down clockwise is the same thing attached to to pipe. Is that how I shut the gas off to house?

Oops size of a dime

No that one is the main gas S/O valve to the house there should be a gas shut off valve close to the water and you need that one to be closed, Thanks.

John

Ok, yes there is. How long to I have to wait after shutting of the gas to disconnect everything to get inside to where the thermocouple is?

Again John, thank you for you help!

As soon as the gas is off, you can tear it apart right away. Is this a sealed combustion water heater, or is it an older water heater? Can you post a pic of your water heater before you tear into it. Some newer water heaters have a diode built into the thermocouple. Do you know how to remove the burner assebly to get to the thermocouple? Normally changing a thermocouple is an easy task. Good luck and let us know how things work out.

Ps, good ideas to spray all joints of gas piping (with soapy water or leak detector) that were unhooked after its all hooked back up again. This way you will make sure you have no leaks.

Mygirlsdad have stated very well, please respond to him and if possible post a picture of your heater.

If you decide to replace the thermocouple like Mygirlsdad says it is a very easy task, please follow the steps below, and see the attachment image.

1. Shut off the gas valve on the water heater and the gas valve on the line near the heater. Remove outer and inner doors, and loosen the pilot and supply tubes and the thermocouple connections to remove the burner assembly.

2. Loosen the screw holding the thermocouple to the bracket. Remove old thermocouple. Bring it with you to the store to ensure you are buying the proper replacement.

3. Install the new thermocouple. Position the thermocouple so that the pilot flame heats 1/2 inch of the tip.

4. Reinstall burner assembly in the water heater. Tighten burner supply tube, pilot tube and thermocouple connections. Tighten thermocouple no more than a quarter turn more than hand-tight.

5. Turn on both gas valves. Check supply tube and pilot tube for leaks with soapy water. If soap bubbles, tighten connections to fix leak. Ignite the pilot light, and make sure the thermocouple tip is heating up. Install the inner and outer doors, good luck.

John