Monitor 441 heater dropping setting to 50 degrees

[msearcher]

I have a monitor that has been fully serviced and is running great, the heater has been set to 76 degrees ( no programming active ) and has dropped to 50 degrees like someone has
hit the clear button. Just installed the heater and have looked at the heater yesterday and don't see anything and seems to be setting the temp correctly.

Planning on switching the front control panel electronics and see if that does it otherwise I will have to swap a main board.

Has anyone see this before? First time for me.

Tom

[msearcher]

Checked the service manual and think it's the resister so will start with that

[Bryand]

Checked the service manual and think it's the resister so will start with that

I am sure this is a stupid question but did you check the reset on the side to ensure it was not moved when installed. Maybe it was moved and the power blinked and it went back to 50.

[msearcher]

Yup, swaped the main circuit board and will wait for feedback

[HayZee518]

thermistor

if its of any help the thermistor when it opens or is not present, the heater defaults to 42 degrees and runs constantly at high output.

[msearcher]

I have checked that - it's in place and working, I have put my finger on it to see if the temp would change and did as expected.

When I checked last night after the board swap the heater had been running with out the issue after 4 hours. Will call this AM and check again (currently it's -8 outside)

[msearcher]

The main board swap took care of the issue.

[msearcher]

After I replaced the main board the women told me that all lights flashed ( frozen fuel line). After thawing the line out I have not heard back from her. When she re-told me the story later she said it was at 50 and I corrected her.

i am not sure now that there was ever a real problem with the heater, I did check with the previous owner and he never had a problem with it dropping to 50 degrees.

[HayZee518]

thermistor

if your unit is the type with the molex plug on the thermistor, have her unplug it and see if the unit goes into high mode.
it will default to 42 degrees and will run wide open.
then have her plug it back in and see where the room temperature goes to. it should read the present room temperature.
if the thermistor was replaced with "other" than an mpi part, could be the span on the thermistor isn't quite correct.

[msearcher]

Thank you HayZee518