Honeywell gas furnace intermittently blowing cold air


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Old 04-04-18, 12:01 AM
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Honeywell gas furnace intermittently blowing cold air

Caveat: I know very little about HVAC systems but am willing to learn.

We have a Honeywell central furnace that came with the house, built in 2011. The model number is N9MPD100J20A2. The serial number is A093359675. It has been working all winter just fine, but just yesterday it started intermittently blowing unheated air into the house. This happened a few years ago as well when the heater turned on for the first time in the winter, but it seemed to have resolved on its own, and we never bothered to look into it. This time the problem seems to be more persistent. We changed the air filter, but that didn't fix anything.

The problem hasn't happened long enough for us to be positive about a pattern, but it seems that the first time the heat comes on after not having been on for a few hours (or, once, when we powered off the Ecobee4 thermostat and powered it back on again), the furnace does blow hot air. When the space reaches the desired temperature, the furnace turns off as expected. The next time the temperature drops below the set temperature, we get cold air.

We have peeked into the furnace (through the peepholes) when it is operating normally, and we see a flame. When it is blowing cold air, there is no flame. I wanted to open up the panel to see what's going on inside as I've read others on the forum have done this, but my husband is wary of opening up the panel of a gas furnace, and the manual says that the power to the furnace will automatically shut off if the panel is open, so we're not sure it would work anyway.

The indicator light is flashing green. We don't see any error codes.

It seems like others who have encountered this problem have fixed it by cleaning a flame sensor. Could that be the culprit in our case, too? Does anyone have any other suggestions? We prefer to troubleshoot this as much as possible before calling in a professional.

Thanks in advance for your help.
 
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Old 04-04-18, 09:28 AM
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Could be anything at this point, without troubleshooting or any error codes to reference.
The bottom blower access door has a switch that opens when you remove the door.
Do you have a meter? You could do some troubleshooting. It may involve working with gas and live electricity.
It may be best to wait until it fails again and look to see the error code it’s flashing.
When was the last time your furnace had a tune up?

That’s not a Honeywell furnace. Honeywell only makes some of the parts used. It’s an ICP furnace.

https://www.manualslib.com/products/...2-3180566.html
 
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Old 04-04-18, 10:02 AM
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Ah, okay, thanks for the information.

Sorry; I wasn't clear earlier. We actually get no error codes even when it's blowing cold air.

It must have been a long time since we've gotten a tune up, certainly at least several years...
 
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Old 04-04-18, 10:04 AM
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No error codes sounds like a control problem.
You’ll have to use your meter to check it when it’s failed to heat.
You should have a checkup every season. By someone who isn’t trying to sell new equipment.
 
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Old 04-05-18, 04:05 PM
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Thanks for your response, roughneck77. So do you mean that we look at the gas meter to see if it's moving forward when it's failed to heat? Yes, I think we'll be getting a tuneup regularly from now on!
 
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Old 04-05-18, 04:38 PM
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It certainly sounds like the furnace is failing on something. Be sure to check for fault codes by looking thru the sight glass on the blower door. Once you open that door or reset the thermostat.... the codes are cleared. You need to see what code is flashing before doing anything else.

Just as a thought... make sure the furnace filter is clean. An overheating problem would fault the furnace.
 
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Old 04-05-18, 05:17 PM
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No, your electrical meter to see if it’s calling for heat.
If it is and the furnace isn’t actively heating, there should be an active error indicating why.
 
 

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