Furnace ignites only 70% of the time


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Old 01-30-13, 09:21 AM
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Furnace ignites only 70% of the time

Hi all, first post on the forum. I have a 20 year old CLARE 60BTU natural gas furnace. 30% of the time, the furnace doesn't ignite, requiring several power cycles to fix it.

Here is what happens when the issue is occurring:

1. Thermostat calls for heat.
2. Inducer motor starts, and stays on indefinitely with no glowing of ignitor and no gas smell/sound.

Power cycling the switch on-off for 5 minutes , works on about the 4th try.

Ive checked that the vacuum sensor is properly closing the contact. I've also held a BBQ lighter near the non-glowing ignitor for a bout 4 minutes, and the burners don't light (not sure if the system delivers gas if it knows the ignitor isn't working).

I'm tempted to replace the ignitor, but since it does glow sometimes, I'm not convinced its the cause of issue.

What else should I be testing?

Thanks in advance!
 
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Old 01-30-13, 11:21 AM
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Once the pressure switch closes, the circuit board should switch on the power to energize the ignitor. After 30 seconds or so has gone by, the circuit board should also turn on the main burner gas for 3 seconds or so.

It sounds like the circuit board isn't turning on the power for the ignitor reliably and not turning on the gas reliably either. It would be a lot more common for the ignition module to fail to turn one or the other on, and rarer to fail to turn both on.

You are correct that since the ignitor lights sometimes the ignitor is not the issue.

Post the make and model of the circuit board or ignition control module. I'd like to see what you have, and an instruction manual for the module would describe the sequence of operation that should be occurring.

Are there any diagnostic lights flashing on the iugnition module?
 
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Old 01-30-13, 04:32 PM
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Hey SeattlePioneer, thanks for the reply.

ICM is a White-Rodgers F50e47-170 (MANUAL). Doesnt look like there are any LED's on this model. The manual describes an initiation of the carbide ignitor 1 second after the vacuum switch is closed, which is not happening.

It then states the ignitor warm-up time is 45 seconds, where after it opens up both gas valves, which also doesnt seem to be happening (proven by the BBQ lighter test).

I'll have a look at my multimeter when I get home, and see if maybe I can test the 120v off of the IGN terminal...

Part of me still wants to say it's due to the vacuum sensor, but last night when I couldnt get it working I tied the two leads from the vacuum sensor together which had no effect. Hmm...
 
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Old 01-30-13, 05:49 PM
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Check carefully to be sure that the pressure switch is closing. If it's not closing, it would produce the symptoms you describe.

I'd use a multimeter to see if the TH connection on the control module is being powered by 24 VAC when the pressure switch closes. If that contact is energized, the power to the ignitor should switch on and the gas valve should turn on after a delay for the HSI to heat up.

So check that carefully. You don't want to replace an expensive part only to discover some other detail was causing the problem.


If the pressure switch is closing, replace the ignition control module.
 
 

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