Intertherm Model MMHA-070ABHR-05 Weird problem

[dans]

Furnace turns on fine by thermostat . Flue motor starts up , burner ignites , blower starts . Normal sequence. BUT THEN burner goes out sometimes blower motor keeps running but flue motor always running. Then burner comes back on then a couple minutes later burner and blower stop and flue motor keeps running then burner kicks back on heats up blower kicks back on. And so on and so on. Tried to use the led on surface igniter module to troubleshoot but looks like ther may be one but isnt working. Had this trouble a few months ago and problem went away but has returned. I work with low voltage circuits in my line of work and can troubleshhot well but looking for any ideas to this weird problem. Thanks in advance and great forum you got here...Dan

[Robert]

Hi Dan,

You can follow the wiring diagram and test circuits with meter to find interruption.

Probably either an electrical problem or a temp problem inside causing a component to open shutting down system.


Trace back from gas valve and test each component and connection to find where the interruption starts from.


Fan switch would be a common place, either through fault or being cooled down quickly causing it to open and close intermittantly.




Thanks,
Robert