Intertherm MH heater
Posted: Fri Nov 26, 2010 3:08 pm
Aloha-
I'm new here but I looks like the place for good info ....
I have a Intertherm mod # MMHA-070AAHR-01 ser # MMH9401-05872
When it gets real cold out the furnace blower fan starts up for a second or two and then quits. The flame never goes out, but the blower fan just starts and restarts. The combustion fans runs all the time also. I replaced the blower fan motor a couple of years ago, and the ignitor several times.
I bought new limit switch (626279) and thermal fan switch (626337). I have switched both of these in and out one at a time between the old and the new to double check it. I have bypassed the upper aux. switch and re-attached it with no difference. With advise of my local HVAC guy I replaced the HSI control (626421) (not just the circuit board) with the original part, not an aftermarket.... The old controller was never flashing a code either.
The gas valve seems to work perfectly- even though the fan switch is bypassed, the thermostat shuts the furnace on and off within limits so it must be OK. I have checked the orifice and burner nozzle for spiders etc...
Now I have the fan switch (thermal) by-passed so I could get heat (-18 here), but the fan has to run all the time now. The ON-OFF-FAN switch seems to work fine.
There seems to be no problems with the wiring w/rodents or anything.
What have I missed, and how can I fix it ????
Thanks, Ron
I'm new here but I looks like the place for good info ....
I have a Intertherm mod # MMHA-070AAHR-01 ser # MMH9401-05872
When it gets real cold out the furnace blower fan starts up for a second or two and then quits. The flame never goes out, but the blower fan just starts and restarts. The combustion fans runs all the time also. I replaced the blower fan motor a couple of years ago, and the ignitor several times.
I bought new limit switch (626279) and thermal fan switch (626337). I have switched both of these in and out one at a time between the old and the new to double check it. I have bypassed the upper aux. switch and re-attached it with no difference. With advise of my local HVAC guy I replaced the HSI control (626421) (not just the circuit board) with the original part, not an aftermarket.... The old controller was never flashing a code either.
The gas valve seems to work perfectly- even though the fan switch is bypassed, the thermostat shuts the furnace on and off within limits so it must be OK. I have checked the orifice and burner nozzle for spiders etc...
Now I have the fan switch (thermal) by-passed so I could get heat (-18 here), but the fan has to run all the time now. The ON-OFF-FAN switch seems to work fine.
There seems to be no problems with the wiring w/rodents or anything.
What have I missed, and how can I fix it ????
Thanks, Ron