I’m puzzled about something that my gas furnace is doing. Maybe it’s normal behavior (I’ve never had a gas furnace before), but it doesn’t make sense to me.
This is the sequence of events:
(1) Normal cycle (temp goes below thermostat setting, thermostat commands heat on, burner fires up, blower comes on, temp goes above setting, thermostat commands heat off, blower continues for a short while before turning off)
(2) A few minutes later, the burner fires up again (not commanded by the thermostat: the temp is still above the thermostat setting and there is no click or “heat on” display). After a few minutes, the blower turns on but only operates for about 15 seconds before shutting down.
…the sequence repeats…
The second event seems pointless and wasteful. Is there an actual reason for it, or is it a problem? I pose this question here because my landlord has not been helpful and I couldn’t find any info online. I don’t know if it helps, but the unit is a Thermo Pride OL11-105RDA converted to natural gas.
Is it a hot air furnace, or a hot water furnace that circulates water through radiators? A hot water furnace will periodically run when the thermostat doesn’t demand heat just to keep the water in the heat exchanger above a minimum temperature. That could be what’s happening. A gas fired steam furnace will do much the same thing.
yeas a boiler will heat itself to keep from freezing. you think why would it need to do this inside a warm building but it does. the air inlet would be open to the outside and cold air will blow into or sink into (basement boiler) easily when it’s really cold out.
It’s not so much to keep from freezing, it’s to provide quicker response. If the boiler is shut down and cold it takes a long time to heat up. By keeping it hot and shutting down the water pumps when the heat isn’t required it shortens the lag between demand and supply.
That certainly makes sense, although I 'm still puzzled about:
(1) why this would happen so soon after the furnace last ran (shouldn’t it already be warm?), and
(2) why the blower runs at all when it does this
eegah, you need to tell us what kind of furnace it is, as best as you can.
Also, what kind of thermostat do you have? I have a “smart” thermostat, and it does some pretty stupid things. I wouldn’t be surprised if mine does what the OP’s does. It cycles a lot more often than it needs to, ostensibly to more gently bring the room up to temperature.
My boiler/furnace has an ‘anti cycling’ system. This is supposed to stop it from switching on and off when the required temperature matches the actual.
A boiler heats water in an enclosed pressure vessel and distributes said water throughout a radiated system. A furnace is a forced air system with ducting; no water. Furnaces have filters, boilers don’t. Boilers have things like aquastats, pressure tanks, etc. Furnaces don’t. That said, the terms are generally interchangeable.
I don’t think it is the thermostat that is commanding this. It makes a “click” sound when it turns the heat on, but the mystery cycle never has an associated click. Plus, the temperature is usually two degrees above the set point when it happens. (it’s a Honeywell RTH2410, in case you still want to know)
I think your blower is independent from the main thermostat, which controls the burner only. At least that’s how it works in my fuel oil furnace.
The blower’s thermostat is sensitive only to the temp inside the furnace. When the temp goes up, the blower turns on; when the temp goes down, the blower turns off. So there’s going to be a lag between the main burner going on and the blower going on; likewise, another delay after the burner goes off and the blower goes off.
That’s for normal operation. If your blower turns on at other times, it’s most likely due to heat buildup in the furnace, for whatever reason. Or perhaps the sensor is in a place which doesn’t heat up or cool down in a perfect, ideal manner.
Just brainstorming here, but what if the internal design is such that the blower only cools down one end of the furnace, and when it shuts off, the other end, which is hotter, gradually heats up the chamber just enough to trigger the blower again and the cycle repeats until things stabilize.
I’ve had all three, a boiler that actually produced steam, a water system that produced hot water, and a hot air system. I now have a heat pump, so I’ve had 'em all, counting the wood stove and fireplace I also had. I didn’t want to assume a hot water system and boiler were interchangeable without the phase change.
Depending on the system. If only one fan then it would be the hot air fan and it can cycle without the burner going off and on. If it is the inducer (Induce draft fan) It will come on before the burner ignites and stay on after the burner goes off.
My question is about the clicking that you are hearing. Is that the stat or at the furnace?
If I called a hot water system a boiler I thought sure one of these pendantic sonsabitches would have chimed in that a boiler implied a phase change from liquid to vapor in the heating medium, and that what I had was a heat exchanger.
