Furnace not blowing heat, but will blow cool?

At some point today, the furnace stopped coming on periodically to blow heat, even though the house was noticeably cooling off. After a few hours, we tried switching the setting on the thermostat from “Auto” to “Fan,” and air did start coming through the vents, but only cool air, even though the temperature on the thermostat was set high.

We tried setting the heat extra high in case some kind of temperature gauge in the system may have been off-kilter; we tried flipping the switch in the circuit panel off and on. Nothing is making any difference.

Any home-repair-knowledgeable people out there have thoughts on what might be happening?

10 Responses to “Furnace not blowing heat, but will blow cool?”

    10 Responses to “Furnace not blowing heat, but will blow cool?”

    1. Avatarjoanna

      That sounds like your pilot light went out (if it’s a gas furnace) or that something is going on with the circuit (if it’s an electric one)…

      Reply to this comment.
    2. Avatarkrasota

      If not the pilot light . . . ours did that when we ran out of gas or oil. Are you on city utilities? If not, when did you last have your tank filled? Failing that, thermostat?

      Reply to this comment.
    3. Avatarbetsyl

      and a third vote for the pilot light. if it’s not the pilot light, you are then at the point where i would call whoever repairs my furnace (in the past, i’ve signed up for the service contract through my gas or electric company) and ask if i could please pay them some money now please.

      Reply to this comment.
    4. AvatarLori

      Gas furnaces less than 25 years old won’t have a pilot light, so I’d suspect a faulty thermostat or sparking mechanism.

      Someone who knows what they’re doing, and I’m not one of them either, could take the cover off the thermostat and short the appropriate pair of wires to see if that would make the furnace turn on.

      Reply to this comment.
    5. AvatarCJ

      It is intriguing that the furnace is not doing anything at all unless it’s on “fan”. When we had a similar problem, the furnace’s blower would come on in response to the thermostat click, but no heat would emerge. We had to take the cover off the furnace and start putting a voltmeter across bits of the heater control stuff. (And then when we needed a repair guy for parts, Rob had to teach HIM how to find the problem.) But yours could well be the thermostat. (Fingers crossed for that one. It’s simpler to fix!) If you have a handy electrical/electronics geek with a voltmeter, you could get pretty far in diagnosing this.

      Reply to this comment.
    6. Avatarhnybny

      G says;

      If it does have a pilot light, that would be the first thing to check. If it does not have a pilot, you need to check the spark ignitor. If you hear a ticking noise when calling for heat, the spark ignitor is probably fine. In that case its probably a thermocouple. If its a thermocouple you’d definitely need a tech to come out and handle that.

      He suggested posting your question at heatinghelp.com on the forum. You’ll get immediate results from professionals in minutes.

      Reply to this comment.
    7. AvatarCarroll

      If it comes down to calling an HVAC company for fixing or a new system, I just last Friday got an estimate from Hiller Plumbing and HVAC. I got them via reference from someone here at work and I liked their representatives and estimates they gave me. I had done alot of research ahead of time and they gave me a reasonable (not cheap Furnace/AC systems aren’t cheap anyway) but decent estimate on the system I wanted. They also give great guarantees on their service and products or your money back.

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    8. AvatarJackson

      If it is a gas furnace it may have a circuit breaker on the unit. That breaker is kinda like the new pilot light for gas furnaces (furni?)

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