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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I had to change batteries on my thermostat abd now it's not

Customer Question

I had to change batteries on my thermostat abd now it's not working. It says 75 U4
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: Just thermostat
JA: Do you plan on doing the work yourself?
Customer: It's am apartment. I called the office but got voicemail
JA: Anything else we should know to help you best?
Customer: It's a White Rodgers model #1F78 NON -PRGM
Submitted: 1 month ago.
Category: HVAC
Expert:  airheatman replied 1 month ago.

UF is not a programmed error code. Lets try a reset

Expert:  airheatman replied 1 month ago.

Should say U4 is not normal error

Customer: replied 1 month ago.
I already did that reset. Saw it online. Just tried it again. Now says 72 what looks like an L with an extra piece going up right side bit not quite making the U shape again and the number 2
Expert:  airheatman replied 1 month ago.

If you remove thermostat from subbase does it stay same?

Customer: replied 1 month ago.
It's now changed to 75 U5
Expert:  airheatman replied 1 month ago.

Doublecheck batteries and make sure polarity is correct

Expert:  airheatman replied 1 month ago.

What numbers follow the 1F78? I will grab a manual

Customer: replied 1 month ago.
There's no other numbers
Customer: replied 1 month ago.
Now the display is gone
Expert:  airheatman replied 1 month ago.

Should be some numbers like 152 or 144 as there are a few models of the 1F78.

There is one trick I have seen work to reset these digital thermostats that works sometimes. That is to remove batteries and install them backwards for 5 seconds, Then remove and install properly,If this does not reset the little computer board in the thermostat you will need to replace the thermostat.

Note: Occasionally , this will not work and will even cause thermostat to start smoking.If so simply remove batteries.If thermostat is not working already, it is worthless anyway, so no harm done .I have seen it work about 20 per cent of the time. So if that is something you are comfortable doing would try it.Could save you having to buy another thermostat.Otherwise, just go ahead and replace it.

Customer: replied 1 month ago.
It's not working. Thanks anyway. I'll have to call someone out.