Furnace Thermostat Doesn't Kick in Unless the Heat is Turned up Very High

[Bill51923]

This is a new very basic Honeywell thermostat. First let me say that I changed out my fan-limit control a couple of days ago because it was short cycling. It still may be with the new one, but not as bad. So, I changed the thermostat hoping that was the problem. The new one is exactly like the old one. But even though the room temp is about 72, the thermostat has to be set well above 80 before the furnace comes on. Any ideas? Thanks.

 

[Jadnashua]

Does the thermostat has an 'anticipation' adjustment? Is the thermostat smart enough to understand the various types of heating (baseboard, forced hot air, radiant, etc,)? That needs to be set for the type you have. Depending on the thermostat, you might be able to hear a relay activate when you increase the setting above the current setting. If the thermostat is sitting in direct sunlight, or in front of a heating duct or light fixture, it might actually not be sensing the room temperature.

A unit could have a timer that forces it to not restart after running for a certain period of time, and that may need adjustment. If you're waiting to hear the blower fan come on, keep in mind, many furnaces will let the burner run for a bit prior to turning the fan on. Have you had someone check to see if turning the thermostat up actually starts the ignition sequence? Depending on the type of unit, that might take up to a minute or so, especially if you tried this in quick succession...with say a gas furnace, it often will wait a bit for any raw gas to dissipate prior to trying to restart.

 

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[Reach4]

But even though the room temp is about 72, the thermostat has to be set well above 80 before the furnace comes on. Any ideas? Thanks

If the room is 72 and you set the thermostat to 75 and the furnace does not come on with in a few minutes, but comes on right away when set to 82, you probably have a bad thermostat. Another possibility is that the thermostat is mounted to a hot wall.

Perhaps take the opportunity to get a thermostat with a schedule and/or WiFi.

Tell us about the new thermostat that you put in.

 

[WorthFlorida]

You need to give the thermostat time to adjust to the ambient air. Also working on the thermostat heat from your hands and breath will throw it off. Be sure no lamps are turned on near it that may give off heat.

 

[Bill51923]

The source of all our furnace woes did indeed turn out to be the thermostat. We had an old basic analog thermostat that worked for years. Then one day the furnace started cycling. We thought it was the limit / fan control, so I changed that, but it didn't help. Then I ran all new wiring from the thermostat to the furnace. Didn't help. Then we redid all the connections there were on the furnace. Didn't help. Finally, two different local HVAC repair guys told me that digital is really the way to go with thermostats, and that going to one my fix things. Sure enough it did. What I don't understand is why the old bare bones Honeywell worked for so many years but replacing it with a new one exactly like it didn't work. I guess maybe Honeywell's newer model may look like the old one but have something different going on inside. Anyway, the new digital one is just s $30 model Ace unit from Ace Hardware. I imagine Honeywell may even make it for them. Who knows? Anyway, it works. All is fine now. Sure was a lot of work just to end up with a quick $30 fix. And this one has an accurate temperature adjustment as well.