Furnace turns off but blower stays running. Waking up to a cold house.

[DaBank]

My mother has a combo heater/Ac unit on her roof that is about 8 years old.

The last few nights the thermostat is set for 72 and she wakes up to the house at 60 and the blower is still on but no heat. The thermostat is still set at 72 and the fan is on auto.
If you turn the thermostat off and back on the heater works again. I went over yesterday and made sure the filter i installed a month ago was clean and went on the roof and blew any dirt out the unit. I watched the igniter and the flame and everything look's good. I verified it was venting out the side.
After about 2 hours the heater stopped and the blower stayed on blower cool air.
Beside air flow or a venting issues want would cause this a faulty high temperature switch? Any DIY tests with a multimeter?
I also noticed the induction fan makes some noise and if you push on it stops. I checked to make sure the screws were tight but the metal cage/housing of the motor is actually loose.
Thanks

 

[Canuck 1]

High limit switch or gas valve

 

[River Runnin]

Thermocouple

 

[napanutt]

Ours did about the same last year. Control board went out.

 

[ChumpChange]

Flux capacitor. That’s all I got.

 

[Bucketlist]

Thermocouple

 

[Orange Juice]

It sounds like an ez fix for an AC service guy.

I tried to fix my last AC unit myself, and figured out quick, I don’t want to own another set of tools I’ll never use.

 

[Riverbound]

It’s tripping on high limit. Could be a number of things. Check for airflow restrictions.

 

[PRIMO]

There is a Slave Cylinder which activates between heat & cold / remove cover , then tap cylinder with ball peen hammer to loosen piston / did this anually on my roof mount / worked every time.....

 

[DaBank]

It’s tripping on high limit. Could be a number of things. Check for airflow restrictions.

I do not see any restrictions. I did notice the flame is not completely blue and has some red to the flame. Was thinking the flue may need to be clean or gas adjusted?

 

[pkbullet]

I asked my son who is an HVAC tech. he said it could be a lot of things. It could be getting too hot. It could be dropping a pressure switch or faulty roll outs. But if the inducer is making noise then it's more then likely going to fail. As for turning the thermostat off and back on that shouldn't do anything. Because if it's an actual issue with the heater it will lock itself out and only cycling power can clear that. I have no idea what any of this means, good luck.

 

[River Runnin]

I have no idea what any of this means, good luck.

It's Fooked up and needs fixed??

 

[TimeBandit]

A new induction fan motor fixed my last heater. The fan was noisy that was my only hint I had to buy it online local supplier wouldn't sell to a homeowner.

 

[4Waters]

I do not see any restrictions. I did notice the flame is not completely blue and has some red to the flame. Was thinking the flue may need to be clean or gas adjusted?

Your evap core could be dirty causing a restriction, next it will freeze up in the summer if it's dirty. See of you can gain access to it to clean it, you might have to research online how to gain access on that unit

 

[Riverbound]

There is a Slave Cylinder which activates between heat & cold / remove cover , then tap cylinder with ball peen hammer to loosen piston / did this anually on my roof mount / worked every time.....

That’s on a heat pump. The poster has a gas/electric no reversing valve.

 

[Riverbound]

I do not see any restrictions. I did notice the flame is not completely blue and has some red to the flame. Was thinking the flue may need to be clean or gas adjusted?

Highly unlikely. Based on your description, It’s shutting off on high limit 99% chance it’s an air flow issue (collapsed duct, clogged filter, dirty coil, closed registers are the most common).

I do enjoy reading all the “diagnostic guesses” in this thread though.

 

[DaBank]

Highly unlikely. Based on your description, It’s shutting off on high limit 99% chance it’s an air flow issue (collapsed duct, clogged filter, dirty coil, closed registers are the most common).

I do enjoy reading all the “diagnostic guesses” in this thread though.

Thank you for the information.
I already checked the filter,coil and all the registers are fully opened.
I will check the ducting but all the registers seem to be flowing the same.
If it is not an air flow issue do you think the high limit switch could be faulty?
Thanks again,
Frank

 

[Riverbound]

Thank you for the information.
I already checked the filter,coil and all the registers are fully opened.
I will check the ducting but all the registers seem to be flowing the same.
If it is not an air flow issue do you think the high limit switch could be faulty?
Thanks again,
Frank

That’s rare but is slight possible. Assuming there are no issues with tune above. I would then move onto checking fan speed, motor operation, gas valve pressure etc.

 

[4Waters]

Highly unlikely. Based on your description, It’s shutting off on high limit 99% chance it’s an air flow issue (collapsed duct, clogged filter, dirty coil, closed registers are the most common).

I do enjoy reading all the “diagnostic guesses” in this thread though.

Was mine one of them?

I swear it's the kanuter valve

 

[DaBank]

I went and cleaned the unit and all the coils with air and then water and cleaned the burners.

The only things I did not clean what the blower motor fan or the induction motor fan.
The induction motor sound horrible and if I move the motor housing it is loose and sounds like the bearings are bad.

I checked all the ducting in the attic to make sure they was no kinks.
All the registers in the house are open and all seem to blow out the same amount.

If the house is at 68 and I set the temperature to say 75 with in 45 minutes the burners will turn off and the control board will flash 2 times for a limit swicth After induction motor is what stays on fault. The induction motor will run continuously until the thermostat is turn off and then back to heat and then the process starts over.

There is a limit swicth on the blower fan partition wall and a limit switch above the burners. Not sure if one of these are bad?
I am also thinking maybe the induction motor is not spinning at enough RPM's is not producing enough airflow?
At this point I am going to buy a new induction motor assembly because it is obviously bad.

This unit is a ICP (Kenmore) PGD330060K001C1.

 

[napanutt]

The induction motor sound horrible and if I move the motor housing it is loose and sounds like the bearings are bad.

I checked all the ducting in the attic to make sure they was no kinks.
All the registers in the house are open and all seem to blow out the same amount.

If the house is at 68 and I set the temperature to say 75 with in 45 minutes the burners will turn off and the control board will flash 2 times for a limit swicth After induction motor is what stays on fault. The induction motor will run continuously until the thermostat is turn off and then back to heat and then the process starts over.

There is a limit swicth on the blower fan partition wall and a limit switch above the burners. Not sure if one of these are bad?
I am also thinking maybe the induction motor is not spinning at enough RPM's is not producing enough airflow?
At this point I am going to buy a new induction motor assembly because it is obviously bad.

This unit is a ICP (Kenmore) PGD330060K001C1.

Ours did about the same last year. Control board went out.

 

[River Runnin]

Did you replace the Thermocouple?