Furnace Won't Turn On, Is My Thermostat the Problem?


Old 11-10-13, 03:22 PM
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Furnace Won't Turn On, Is My Thermostat the Problem?

Hello, I'm hoping someone here can point me in the right direction.

I have this house that I am trying to sell months after I have moved out. It's getting close to the winter and might not sell until spring, so I wanted to set the heat to come on at a point to ensure that the pipes won't freeze in cold weather. I had left it at about 55 degrees and didn't revisit the house for about a month.

Well, the last time I was there, I noticed that when I tried to turn the heat on, nothing happened, and that the house was too cold for it to be working properly. This was an evening in the upper 30s.

I have an old honeywell dial thermostat that has two separate switches on the side, in addition to the rotary dial. One switch toggles from cool, to off, to heat. The other controls the fan separately and toggles from on to off to auto.

Here's the strange thing: When I set the fan to on, it immediately starts blowing, but only if the other switch is set to cool, or off. The moment I switch it to heat, the fan shuts off and nothing happens.

Now, this is a heat forced air furnace and I have ensured power and gas is getting to it.

So, at this point, I'm wondering what could be wrong that would cause the fan to immediately shut off when in the on position, but only when I also engage the heat.

Any thoughts or suggestions? Could this simply be that my thermostat has broken in some way, or is my problem with the furnace? It worked just fine for 4 years. And, when I turn the thermostat to cool it engages the air conditioner outside just fine. This makes me think the issue isn't the thermostat. But, I am only a lay person with regard to hvac, obviously.

If anyone could point me in the right direction on this, I would be sincerely appreciative.

Josh from Illinois
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Old 11-10-13, 03:49 PM
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I suggest you go to the furnace and find the terminals where the thermostat wiring attaches. Find the "R" and the "W" terminals and use a small wire to jumper between them. If the furnace starts it would indicate a problem with the thermostat or wiring issue between the thermostat and furnace.
Old 11-10-13, 03:50 PM
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Welcome to the forums.

It sounds more like a problem with the furnace.

Set the thermostat to off. Go to furnace and look for where thermostat wiring comes in. Look at connection point or control box. Look for R and W terminals. Try shorting them together and see if the furnace starts to heat.
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