I'm having issues with my Honeywell RTH7600D thermostat. It's a couple of years old and has worked fine until recently.

We're in Southern California and the cold weather has recently started so I went to check the thermostat. The display was blank and the batteries were dead, so I replaced them. This brought the thermostat "back to life", except for one thing: it does not display the current temperature anymore. The LCD display simply shows two dashes where the temperature should be. I can turn on the fan, and it starts blowing, but I cannot set the target temperature or turn on the heater.

We do not have an air conditioner, just a gas heater. I have cycled the power on the heater and on the thermostat (by disconnecting it and removing batteries), without success.

I have researched this issue online, but the only results I get from googling are pages that address a completely blank display on the thermostat (by replacing the batteries). This is not really the issue I'm having - I can work the controls and turn the fan on/off.

It looks to me like either a faulty thermostat, a failed (or failing) connection between the thermostat and the temperature sensor, or a furnace problem.

Can anyone suggest additional steps to troubleshoot this problem?

  • Does your thermostat have any sort of remote temperature sensor accessory? Does the heater work when you jumper R to W? – ThreePhaseEel Dec 21 '17 at 23:47
  • Thank you for your help! As far as I know it does not have a remote temperature sensor. When I jump R to W, the fan comes on. I let it run for a few minutes but it did not appear to heat up. – Kryten Dec 22 '17 at 1:13
  • If you jump R to W, can you then see/hear that the heater is actually functioning? (You may have to take the cover off + bypass the service interlock to do this) – ThreePhaseEel Dec 22 '17 at 1:31
  • Yes, when I jump R to W, the fan comes on - air is blown out of the registers, I can hear the fan come on and run. But the air does not heat up. – Kryten Dec 22 '17 at 1:54
  • Can you take the cover off and bypass the service interlock so you can actually see the burners fire? – ThreePhaseEel Dec 22 '17 at 2:10

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