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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Honeywell PC8900 thermostat. The screen is blank and

Customer Question

I have a Honeywell PC8900 thermostat. The screen is blank and my furnace is not working. I phoned an HVAC company and they said to check if the battery needs replacing. I have pulled the part of the until that disconnects off the wall, but if I turn it over, there is no visible battery compartment, unless perhaps I need to take off the two screws that are on the back panel. Does this unit have a battery or is it possibly something else that is the problem. I said I would try and troubleshoot this myself, but if I can't, I will need to call in an HVAC technician.
JA: Sometimes HVAC issues that that you think will be really complicated end up being easy to fix. The HVAC Technician I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the HVAC Technician should be aware of?
Customer: Not that I can think of at the moment. We have an on/off switch in the basement that also turns the furnace on/off, and it was suggested that I turn it off and on and see if the thermostat would "reboot" itself, it did reboot once but then went off again, and I have tried this twice again with no success.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.
hello, My name is***** are no batteries in this unit. Are you able to get to the furnace for a few checks? And do you have the panel W8900 at the furnace?
Customer: replied 1 year ago.
Yes, I just opened the unit and confirmed that there are no batteries. I can go and do some checks at the furnace if you let me know what I should do. I don't see anything like the panel you are asking about at the furnace - would this be some kind of digital panel with some kind or readout? If so, there is nothing like that at the furnace. The furnace is a HEIL Ultima II
Expert:  BillyHvac replied 1 year ago.
this thermostat is commonly used with a interface board.But...can you tell me if there is a light present on a circuit board in lower section of furnace?
Customer: replied 1 year ago.
Not that I can see. There is a small light on the electronic air cleaning unit, but that's it.
Expert:  airheatman replied 1 year ago.
Do you have a volt meter for troubleshooting and can you give me model on the furnace?
Expert:  airheatman replied 1 year ago.
Ultima !! is a series.Model will be on a label just above burners on right or left inside panel
Customer: replied 1 year ago.
I'm sure we have a voltmeter somewhere, but would have to find out where it is. I don't see the model number panel you gave me the link to anywhere on the unit. There are some panels with warnings, but nothing like the photo in the link.
Expert:  airheatman replied 1 year ago.
Look on the control board on furnace and see if maybe there is a small auto type fuse blown.
Customer: replied 1 year ago.
Thank you I brought a technician in and the problem was solved in 15 min, it was an issue with the thermostat.
Expert:  airheatman replied 1 year ago.
Glad you got it taken care of.