Funny thing today. I noticed my heater wasn’t working. The gas would come on, but not the blower. So, I turned everything off (at the thermostat) just to see what would happen if I turned it back on again. The blower then worked for a minute or so. Turned the thermostat back on and same problem-- gas, but no fan.
Then I just turned the fan to “on” from “auto”, turned the heat back on and everything works fine. Note: I have a 2-zone system and I get the same result from both zones.
First question: Is this a safety issue?
Second question: Anyone have any idea what’s going on?
For the furnace to blow hot air up to the house, you’ll hear 3 things…
1)The inducer. A small blower, it’s the first thing you hear making noise.
2)The gas firing. This heats the plenum (the air above the furnace) for a few minutes
3)The main blower turns on and blows warm air into the house.
Shutting down is, more or less, the opposite of this.
I assume you’re hearing the inducer, then the gas (and fire) but not the main blower. Is that correct?
If that’s the case it could just be the fan switch that needs to be replaced. The fan switch keeps an eye on the temperature inside the furnace and turns the main blower on when it gets hot enough (so you don’t blow a bunch of cold air into the house) and shuts the fan off when it cools back down (which is why the fan runs for a few minutes after you hear everything else shut down).
Something you can do is take off the bottom panel and check for trouble code on the board.
Rethinking this, you said both zones are giving you the same problems. Zones can be set up differently. I assume you’re talking about two different furnaces both controlled by one t-stat…check the batteries in your t-stat. I’m willing to bet they’re dying. They’re turning on your furnace but don’t have enough voltage to maintain that and when they die the furnace shuts back off.
My guess (without any more info) is that if you replace the batteries your problems will go away.
There’s some other sensors and switches in there, but if you have two furnaces giving you identical problems, you have something else going on.
The only other thing I can suggest is that you go outside and check the intake/exhaust pipes and make sure they’re not clogged (bird’s nest, neighbor’s stuffed a tennis ball in the pipe etc, leaves (snow it cold climates) packed up against it). Typically that problem will make the unit shut down before the gas fires, but a partial clog might make it act differently.
Does your furnace have an error code? This happened to us last week. The error code said that either a vent was blocked (unlikely) or something was stuck, and that it would turn itself off and restart. It did and all is fine.
For our furnace there is a red light which is steady when things are fine, but which blinks a code when something is broken. It was useful to figure this out. I suspect most newish furnaces would have something similar.
If it’s throwing the ‘vent blocked’ code, it’ll shut down before the gas fires. Having said that, sometimes it’s just the switch that’s broken. On my parent’s furnace that switch broke a few months back. Funny thing was, when I took it out, I just played with it for a few minutes, popped it back in and it’s been working fine ever since.
Most gas utilities are allowed to offer repairs to furnaces and are required to respond in a reasonable time frame in emergency situations. Today is January 11th, and while you may live in a warmer state, some states are Not.
If you are calling your utility to schedule an emergency repair because your furnace has stopped working, please MAKE SURE you tell them that you have** “NO HEAT”**.
If you have small children, tell them that too please.
I’d say it is the heat sensor unit on the end of a wire from the switch. Don’t remember the name, but you’ll see one in a gas kitchen stove as well as the hot water heater. THis sensor can go bad. I’d pull it out if you feel competent to do so and take it to a suplier and buy a new one. We used to carry them in the truck when we went out on service calls.
If you were able to call for heat from the thermostat and the burner lit up and ran for a minute or so before shutting off and the blower didn’t run at all, the stack limit switch takes over and shuts off the burner before the furnace overheats.
IME, a failed or wonky flame sensor cuts the gas off pretty quickly - something in the order of five seconds. Its job is to be sure the burner actually lit, rather than just dumping unburned gas into the room. If the burner is cutting off quickly, the first thing to try would be to clean the sensor - they often just get dirty enough to not see the flame.
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That was weird. It’s like I closed windows and then booted it up again…
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Considering how most modern furnaces are driven by a small microprocessor, it’s a fair analogy. There is a small chance the thing just got confused and cutting power to reboot it was all you needed. If not, something like the blower switch or flame sensor is failing, or as mentioned above, the thermostat’s batteries are dying. I’d try replacing the batteries before looking at more expensive and/or unlikely problems.
It’s also possible the thermostat is bad - a while back, we had no heat, but power-cycling the system let it work for one heat cycle. The service guy sent by our landlord replaced the stat and all was well.