Question about Honeywell Programmable Thermostat Heater

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Backlight light out thermostat have no batteries in it

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What has happened, since you do not have batteries in this stat and it is showing no display, you have lost the 24 volt power to your stat. I don't know the age of the unit, but you need to go to the indoor unit and pull off either one or both panels. Find the circuit board . If it is fairly new, you will have a control board and it will have a plug in type fuse in it. Its the same type that your auto uses. It will be a 3 to 5 amp fuse. Using a flash light, check to see if it looks blown. If you are not sure, shut off the power and remove it. Replace it with one that is good. This should restore power back to the stat. Make sure you put the panels back on properly, as you may have a safety switch on the perimeter, and if there not on right the power will be off. This switch has to be closed by the panel. If it keeps blowing the fuse, you have a dead short somewhere in the unit. It will be in the control/24 low voltage section of the heater.It would help if you could tell me what kind of unit you have, name, model, serial, number, if it is a gas heater. If it has a indoor unit and outdoor unit, and so on. Check out this fuse as they sometimes just get weak and blow. Hopefully that's what it is. Please let me know what you find. Please don't forget to rate me as I know you will be kind, and I will be checking back in on you.
A/C, Heating, & Refrigeration Contractor

Posted on Sep 06, 2010


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