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Monday, January 5. 2009

Thermocouples

Thermocouples are cool little items, conductors which generate a voltage when subjected to a thermal gradient (Wiki). That's the old thermoelectric effect that you remember from high school physics.


The effect was accidentally discovered by the Estonian Thomas Seebek in 1822. Most of our general-use thermocouples are the inexpensive K-type, Nickel-Chromium and Nickel-Aluminium.


I had the unfortunate opportunity to learn more about our dependence on these mechanisms over the weekend. Among hundreds of other things they are used for, I learned that they control the pilot light on gas water heaters. If the pilot light goes out and your thermocouple sensor is on the blink - no hot water.

Posted by The Barrister in Our Essays, The Culture, "Culture," Pop Culture and Recreation at 14:00 | Comments (5) | Trackbacks (0)

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That probably explains why my gas fireplace is on the fritz.
#1 Retread on 2009-01-05 14:00 (Reply)
The thermocouple on your gas water heater is probably a pressure thermocouple. A small closed device with a tiny bulb exposed to the pilot flame that is connected by a small diameter metal tube to a small metal diaphragm or bellows. When heat is applied to the bulb the gas captured in the bulb/bellows expands, exerting this force against the diaphragm/bellows which opens a small valve that supplies fuel to the pilot light and 'pilot pressure' to an actuator for the main fuel valve of the appliance. This prevents the main valve from opening if there is no means of ignition (pilot light) when the system thermostat calls for heat. This condition would continually deliver gas to the building until some other source of ignition set the whole thing off. When you initially light one of these appliances you manually hold open the pilot valve to deliver gas to the pilot so that it can be ignited. Holding the valve open until enough heat has been delivered to move the bellows and open the valve.
#2 lenf on 2009-01-05 18:32 (Reply)
Anything with a standing pilot will have one.

Even systems without a constant pilot, will often use one to make sure that the flame they (think that they) lit is still burning - rather than fill the house with gas.

I have replaced them on water heaters and space heaters - for myself and the odd cold friend.
#3 Rob on 2009-01-05 18:34 (Reply)
If you have a Whirlpool model water heater the control assembly was probably faulty. I had installed my unit four months prior to the control failure so I called the 'trouble shooting hot line' and they sent me another controller the next day for free. Yes I was pissed that something so new failed but they did make good on it. I would have been really irritated if I had to pay for the unit or for someone to install it.

Sometimes it pays to be handy.

Either way it is amazing how we take things for granted until their not there for us.
#4 Teo on 2009-01-05 21:19 (Reply)
My dad had to replace his entire gas furnace this past month because of a faulty gas control unit/ thermocouple on an obsolete Singer unit. I didn't ask him how much. First the gas company wouldn't fill his tank. Code violation, my ex-brother-in-law built the extended porch too close to the old underground tank. After the new tank was in the furnace still wouldn't start, it took them a week to figure out the problem. It's fortunate that we were having some mild weather here in central FL.
#5 JimK on 2009-01-06 08:24 (Reply)

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