Lennox G10 q3-82

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Old 10-25-08, 08:34 AM
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Lennox G10 q3-82

Have a Lennox G10 q3-82 that won't start. Manual pilot is lit but turn on thermostat and burner does not come on. The fan runs if you turn the thermostat on to fan only but nothing on automatic, assuming that is because the burners aren't on.

Any help?

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Old 10-25-08, 12:29 PM
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You are probably assuming right.

Is this an older furnace without the module and pressure switch and ventor fan? Tell us as much as you can describe about what this furnace has.

Do you have stat set to "heat" and "auto"? If yes, you could jumper inside the furnace between R and W on the low voltage terminal block inside, and see if it goes. If it did, you have a bad thermostat or bad thermostat wire or connection (maybe on the back of the stat). But always do repeat tests with and without jumpers, to rule out coincidence of it now starting to work on it's own.

When you turn on thermostat, you could see if 24 volts makes it to two MV terminals on the gas valve.

If you have no 24 volts there, be sure stat works. Another way to check the stat is to disconnect the red(R) or white(W) terminal wire off the screw terminal and use ohms setting on meter between the two wires, and with the furnace off, turn up the stat and see if you get 100% continuity. If you do, the stat works.

If you confirmed the stat works for heat (not just for "fan on"), and you have no 24 volts that comes to the gas valve after the stat is turned up (wait a short bit for possible relay to energize first),then you will have to trace the 24 volt wires from the gas valve on back, and maybe suspect a bad relay.

If you DO get 24 volts at the gas valve between 2 wires on the gas valve, and only at the time the main gas valve should open, so you know you are testing the right terminals -if you only have 2 wires on it (or do you have more, and if so, what is printed next to them?), then that means something is not letting the gas into the burners or not good enough. Either the gas valve got stuck from sitting all summer and maybe a few gentle raps on it will allow it to open, or there is something blocked not letting the gas to get right to the pilot flame area, or the gas valve is beyond help and needs replacing.

If the gas valve IS getting current and the valve inside is trying to open, you should also be able to hear a slight little click sound or feel it in your fingertips if you rest them on the valve.

If ever you try something like rapping on valves, pipes, etc., it is always a good idea to be ready to be able to shut off the gas incase something went wrong. (Albeit simple raps say with plastic handle of screwdriver should cause no problem) Same with in plumbing, you want to be able to quickly shut off the main water valve if you are tampering with fixtures, fittings, etc.
 
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