Hi everyone. My Honeywell Chronotherm IV Plus thermostat has always worked great but for some reason hasn't been heating since yesterday. I use the "Hold" function and set it to a temperature which it then heats to and holds.

Since last night, I've had the heater set to 75 but the temperature in the house (according to the display) is 68. The display even has the little flame icon which usually is on when the heater is running. Any help is appreciated.

I've checked all the little things to make sure I'm not making a bonehead mistake (i.e. making sure it's set to heat, that the temperature desired is above the room temperature) but can't figure it out. Thanks.

Do you know how to disconnect the wires in the furnace (the thermostat wires),, disconnect from the r post and the w post,, connect the 2 post together with a jumper wire, see if the furnace comes on and works proper,(it won`t stop running as long as jumper is in place),, if furnace works OK ,yes you either have tstat problems or with the wiring between tstat and furnace

do you know how to disconnect the wires in the furnace (the thermostat wires),,,disconnect from the r post and the w post ,,,connect the 2 post together with a jumper wire,,see if the furnace comes on and works proper,(it won`t stop running as long as jumper is in place),,,if furnace works ok ,yes you either have tstat problems or with the wiring between tstat and furnace

I'm not sure how but I'll try my best to figure it out :D thanks

Check this: remove the thermostat from the sub-base and see if the contact pins and/or strips look oxidized. Carefully cleaning them with a fine abrasive will restore electrical contact if lost.

Did you figure this out?
Im having the same problem. Was it thermostat or furnace issue?