Miller CMF 80 PG Furnace error

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Old 11-27-17, 10:24 AM
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Miller CMF 80 PG Furnace error

Hello,

I have a miller/nordyne cmf 80 PG gas furnace for a mobile home. The furnace is running through the ignition sequence but fails to stay running. Once it shuts down the light on the HSI blinks three times. We have tried everything we can think of to find a solution to this problem but no luck, any ideas?

We have replaced the draft inducer motor, the flame sensor is connected to the ignition switch which we have replaced. I have checked all of the electrical for the furnace and everything is in working order. The heat exchanger is not cracked, and the limit control switch is working properly.

Please help!!
 
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Old 11-27-17, 11:04 AM
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Three flashes is flame failure. Do the main burners light ?
 
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Old 11-27-17, 04:26 PM
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Yes, the burner will light and stay light until the system shuts down.
 
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Old 11-27-17, 04:46 PM
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Welcome to the forums.

Once the burner lights.... how long is it staying lit before it shuts down.

Tough furnace to work on with that gun type burner. I see mention of a flame sensor but don't see a sensor rod which means it may use the igniter as a flame sensor.

Better manual..... enora/nortek/hvac/literature/067a.pdf
Additonal Manual.... nordyne_cmf_100-po.pdf
 
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Old 11-28-17, 05:00 AM
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The whole process of start-up takes 1 min 40 sec. The burner is lit for 1 min before the whole thing shuts down.
 

Last edited by Melissa5599; 11-28-17 at 05:04 AM. Reason: Wrong word
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Old 11-28-17, 11:46 AM
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Ok.... then it's not a flame sense issue. It's an overheat issue.

Take the cover off the limit control and verify that is is turning while the burner is running, If it's an overheat issue.... that dial should turn past the "FAN ON" point and continue to the limit area.

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Old 11-28-17, 01:17 PM
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The fan limit barely moves. They flame is not on long enough to generate enough heat to turn it. I do know that the fan limit works though. When the thermostat calls for heat, the inducer motor starts and runs for 40 sec. before the ingnitor lights. Then in the remaining minute that it is running, there is a flame but it does 3 short burst of gas. Could it be something with the gas line?
 
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Old 11-28-17, 02:25 PM
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It's pretty rare that it could do bursts like that. Usually the flame sense will trip unless the pause between bursts is too short.

Do you have a voltmeter ? It would be good to check the voltage to the gas valve when it's firing. It should not waiver and be near to 24vac.
 
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Old 11-28-17, 05:43 PM
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We checked the voltage to the gas valve. When it first comes on it shows 23.7 then right before it shuts off, it jumps to 24.3.
 
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