MGHA-066ABFC-01 Nordyne Intertherm won't shut off

[paigeroni]

I came home to a 91 degree house tonight (mid-Dec) and the furnace wouldn't shut off unless I turned it off at the electrical main box.

Too late to call HVAC repair. Temporary solution: I switched it to AC and set the temp to 75 degrees. Once it hit that mark, the unit turned off, and I set the thermostat to Heat OFF. All is quiet.

However, I would like to know what the problem might be. The furnace doesn't pay attention to the thermostat settings. It won't even shut off when the thermostat (LUX 9000) is turned to HEAT OFF. I reset the thermostat - furnace still running. Only turning off at the electric box worked, but then I read that gas should be shut off if you do that. Had me worried.

For now the furnace is off and I can use my portable elec heater for the night. Has anyone had this problem of a furnace that won't quit heating when it reaches the thermostat setting? (Hate to see my gas bill!)

Thanks!
Elise
Troutdale, Ore.

[Robert]

Hi Elise,

Could be the thermostat or a faulty ignition control module.

At the module, you can test or get someone who can and see if you have 24vac across C and W with no call for heat at t-stat.

Set t-stat to come on with heat, then change to heat-auto-55.


IF heat stays on, do above test.

IF you have 24vac, t-stat is bad or short in wiring between t-stat and control.

IF you do not have 24vac at C and W, test at C and GV for 24vac.

IF you do not have 24vac at C and W, BUT have it at C and GV, the control module is bad.



Thanks,
Robert

[paigeroni]

Thanks for your reply, Robert! I tried the Heat - Auto - 55 degrees suggestion and messed around with the thermostat. Somehow the heater started to behave again and has all weekend. Good thing since we're having a bit of a chilly winter storm here in Oregon!

Elise

[Robert]

Hi Elise,

You're very welcome, happy to help.


Take care and best wishes,
Robert