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I need to turn off the breaker for the furnace but am afraid this will turn off the pilot light to my gas furnace & I don't know how to relight it. Are any special steps necessary to prevent turning off the pilot?

.This is a Lennox G2 Series Gas Furnace Model # G20Q2E-75-C1

Updated Question with the info on furnace . It is a Lennox Gas furnace Model G20Q2E-75-C1.

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Without information like the make/model, this is impossible to answer. Be prepared to re-light your pilot; if you don't know how or are not comfortable doing so, contact a licensed HVAC service person. Plan for the worst (that it will go out). –  Steven Feb 25 '13 at 19:40
    
Unit is listed as having electronic ignition: completeheating.ca/Old/manuals/LennoxG20.pdf –  HerrBag Feb 25 '13 at 21:07
    
From the manual HerrBag posted, it looks like your pilot may be automatically controlled by the Robertshaw Electronic Ignition. If your furnace has a control that looks like the one at the top of page 6 (Figure 7), you don't need to do anything about the pilot - the furnace always handles it. –  Chris Marasti-Georg Feb 26 '13 at 15:20

3 Answers 3

Gas appliances tend to use a thermocouple (which is a self-powering device) to keep the gas valve to the pilot light open. This means that the light will not go out when you turn off the breaker. Thermocouples are pretty interesting - learn more on Wikipedia here.

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If your furnace isn't hooked up to any power whatsoever, how does it circulate air? –  The Evil Greebo Feb 25 '13 at 19:36
    
@TheEvilGreebo ack, I read the question as water heater, not furnace. Will update. –  Chris Marasti-Georg Feb 25 '13 at 19:38
    
clarification, thermocouples (also called thermopiles) are actually self-powered, generating small voltages when heated. –  HerrBag Feb 25 '13 at 19:41
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No worries. @339sevenoaks - Chris has the right of it - your pilot light is not controlled by power from the breaker box. –  The Evil Greebo Feb 25 '13 at 19:53
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@HerrBag A thermocouple is a sensing device that produces very low voltages (µV). A thermopile is a collection of thermocouples connected together to create a larger voltage (mV). –  Tester101 Feb 26 '13 at 13:58

If your pilot light does go out, these are the steps to re-ignite.

  1. Turn the pilot valve control knob all the way to OFF
  2. Wait 10 minutes to allow any lingering gas to dissipate. There shouldn't be any but this is just a play it safe step.
  3. Turn the pilot valve to the PILOT position. In this position the knob can be depressed. When depressed, gas will flow to the pilot light.

  4. Press the knob in, and quickly light the light and then KEEP the knob pushed down

  5. Hold the light down for at least a minute.
  6. Release the knob If the light goes out again that means that the light wasn't on long enough for the thermocouple to get hot enough to register that the light was lit. In that case, immediately return to step 4

  7. If the flame stays lit, turn the knob from PILOT to ON.

Congratulations, your pilot light has been re-lit.

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Usually they recommend you wait 10min if you need to retry steps 4-6... –  Steven Feb 25 '13 at 21:22
    
Yeah, but if you do that the thermocouple cools down and you need to hold it in even longer. (Actually, I light a plumbers torch and blast the thermocouple with that. 5 seconds of that and it's good to go...) –  The Evil Greebo Feb 25 '13 at 21:25
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DIY - Helping people learn new bad habits every day! :P –  Steven Feb 25 '13 at 21:32
    
I second the comment from @Steven. The idea to use a torch to blast the thermocouple is a pretty bad habit to get into doing -- and then to bring it up in a site meant to promote the proper way to do things ... not so great. –  Michael Karas Feb 26 '13 at 12:10
    
I challenge you to defend the assertion that it's a "bad habit". A burning pilot light applies constant flame heat to the thermocouple. A plumbers torch does the same thing just heats it up more quickly as the heat is more intense. It's no different in my view than holding a lighter up against it constantly to warm it up, and a lot faster. Between doing that for 5 seconds and holding down the hard, uncomfortable pilot light for up to two minutes waiting for the TC to come to temp, I'll take the rapid heating. –  The Evil Greebo Feb 26 '13 at 13:09

Depending on how the furnace is wired, the pilot may or may not go out.

Transformer Powered Gas Valve

In some installations, the gas valve is powered by the 24V transformer. In a situation like this, a thermocouple is used to detect the flame. The voltage generated by the thermocouple is sensed by control circuitry, which in turn controls the operation of the gas valve. If the furnace loses power, the transformer is powered down, the gas valve closes, and the pilot goes out.

This seems to be found less in newer furnaces, though may still be encountered from time to time in older installations.

Self Powered Gas Valve

In other installations, a low voltage gas valve is used in conjunction with a thermopile. This allows the pilot to stay lit, even when power to the furnace is lost. With a setup like this, the heat from the pilot actually provides all the power the pilot assembly needs to control the valve. Which means as long as the pilot is burning, the valve will stay open (given the thermopile does not fail).

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