Furnace not starting


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Old 11-24-08, 12:47 PM
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Furnace not starting

I have a Comfortmaker gas furnace with a White Rogers 50A52-111 control and a programmable thermostat. In the morning when the thermostat switches from the sleep setting to the wake setting the furnace will not start unless I move the thermostat cool/off/heat switch to off and back to heat. This is the third thermostat and it did the same thing with all thee.
Once the furnace is on, most of the time during the day it will work but not always and when it won't light I again have to move the switch off and back to on.
 
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Old 11-24-08, 03:08 PM
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We need to know if the inducer fan tries to start up.

A couple years ago I had one with same symptom and came to the conclusion that the cold in the basement, from over night temp set back, was affecting the contacts in a sequencer or heat relay, and a new one of those got the furnace running/no call backs to that place since. It usually ran during the day, but not after the people got up in the morning and wanted it warmer.

If the inducer fan DOES start up (the above would not apply), then you need to catch this thing doing it (actualy look in the furnace where the burner compartment is), and report as to what you see. Like - is the ignition occuring?, where you get a spark?, or a spark with a pilot to come on?, or an HSI coil to glow bright?

If you have a hard time catching it in the act, you'd have to do certain things to rule those out, like - clean a flame sensor, blow out the condensate drain hose, disconnect the vacuum tube from a pressure switch and clean out the ends where it plugs into, remove connectors that are at the ignition module or board and reinstalkl these to make sure all make good contact, to loosen and retighten the thermostat wires in the furnace (only if the inducer does not come on, for this last thing mentioned)
 
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Old 11-24-08, 04:08 PM
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The inducer fan does not start. From what I have been able to tell nothing happens when the thermostat calls for heat until I switch it off and back on.
Is the heat relay/sequencer part of the control module or separate.
 
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Old 11-24-08, 04:33 PM
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On newer furnaces that have boards, it should be on the board. Likely one of the black square boxes.

But you are going to have to make sure that when you believe the stat is calling for heat, that down in the furnace you are getting 24 volts at the W terminal, where the thin low volt wires hook up.

It be odd for the inducer motor to be sporadically malfunctioning. But you could test for current going to it, to confirm.

You may want to remove the board, so you can closely inspect both sides of the board, for signs of bad/loose solder.

And you said, "from what I (can) tell". Well, you need to know, otherwise we could go off on some goose chase for nothing. Be sure you at least go to furnace and listen for it if it runs or not.
 
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Old 11-24-08, 06:34 PM
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I know there is 24V at the w terminal when calling for heat, The stat is about 18 inches from the closet the furnace is in so it is easy to hear the gas valve and inducer motor and burner light off.
 
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Old 11-25-08, 08:51 AM
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Yesterday I cleaned and checked all the spade terminal connectors on the system. This morning it started when the stat called for heat. I see how it goes over the next few days.
 
 

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