Furnace blower sometimes kicks back on after heating

[Bminder]

I've got an older Rheem natural gas forced air furnace.
This winter we've noticed that sometimes, not every time, but sometimes after it's run it's heating cycle and shut off, a couple minutes later the blower comes on for a minute or so.
I know that this is a safety feature, and that it thinks the heat exchanger is still too hot, so it runs to cool it off.
But why would it start doing that this winter?
It maybe does it one out of 6 or 7 cycles. Seems random.

Any ideas or things to check?
The only thing that is different is I put a new filter in a couple months ago and it's a different brand I've never used, and it's supposed to be on of those kind that removes 99.999999999999% of the particulates, but I always use those kind of filters, just not this brand...

Thanks.

 

[Rockhead261]

The filter is blocking normal convection which previously cooled the heat exchanger. Those filters are a complete joke in residential applications. A true particulate filter will fill a small garage. Toss it, use a standard fiberglass filter, and replace it often.

 

[Bminder]

Thanks Rockhead, I was thinking I should do that.

 

[zmaxmotorsports]

Just install a standard pleated filter,not the fancy one.

 

[Rockhead261]

Meh on the pleated ones as well. An older furnace (like the OP's) was designed for 1" fiberglass. They're still the best bet for residential applications.

 

[Showkey]

How old is the furnace ? Does it have the old style blower fan temp switches ?

 

[bonneyman]

How old is the furnace ? Does it have the old style blower fan temp switches ?

Yep, these old combo mechanical controls were known to do the multiple-blower-on-several times after cycle off.
That, and a heating fan speed set too high. It cools off the switch too quickly after the burners go off, and the blower turns off. But there's enough residual heat to bring the switch back on again.

 

[Bminder]

I'll have to look and see if it has that kind of temp switches.
The house was built in '87, and it's the original furnace.
I opened it up to replace the filter, and the spring that holds it in place had popped off so the filter was just laying in there, so it couldn't have been causing a restriction.
I'll check the temp switch gizmo tomorrow and post what it is.
Thanks.

 

[zmaxmotorsports]

I'll have to look and see if it has that kind of temp switches.
The house was built in '87, and it's the original furnace.
I opened it up to replace the filter, and the spring that holds it in place had popped off so the filter was just laying in there, so it couldn't have been causing a restriction.
I'll check the temp switch gizmo tomorrow and post what it is.
Thanks.

That should be the old style furnace if its an 86-87,Ive never had issues with the standard pleated filters causing a restriction in them.
Anyway if the filter wasnt restricting anything Id probably pull the limit switch out and replace it.
Youll need to pull it out and measure the length of the shaft to get the right replacement for it.
take a picture of the wiring so you can hook it back up the same,and check to see if the jumper has been removed in the bottom so you can do the same to new one.

 

[Bminder]

That should be the old style furnace if its an 86-87,Ive never had issues with the standard pleated filters causing a restriction in them.
Anyway if the filter wasnt restricting anything Id probably pull the limit switch out and replace it.
Youll need to pull it out and measure the length of the shaft to get the right replacement for it.
take a picture of the wiring so you can hook it back up the same,and check to see if the jumper has been removed in the bottom so you can do the same to new one.

Now it doesn't do it every time the furnace runs, only once in awhile. It might go a bunch of times without doing it.
Would it still be worth replacing the limit switch?

And where is that fan limit switch located?

 

[zmaxmotorsports]

Now it doesn't do it every time the furnace runs, only once in awhile. It might go a bunch of times without doing it.
Would it still be worth replacing the limit switch?

And where is that fan limit switch located?

Id atleast pull it out to see which one you need,you can always put the old one back in and keep the new one sitting on a shelf for when it goes completely belly up,which they tend to do on a really cold night when everybody is closed.

 

[Bminder]

So where is the limit switch? Here's a photo:

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[zmaxmotorsports]

Straight above gas valve on right side,cover pulls off of it.

 

[Bminder]

And it's a Rheem, not a Lennox... brain fart.

.

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[zmaxmotorsports]

And it's a Rheem, not a Lennox... brain fart.

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I was thinking rheem when I saw the color and burners.(I was a weather king dealer for a few years)

 

[Bminder]

Thanks, haha.
So where can I go to get a new limit switch? Is there an online resource? And a site with a manual?

 

[zmaxmotorsports]

Check your private messages,I sent you the phone number for a place I like buying stuff.
Theyre normally as cheap if not cheaper than on line.

 

[janetfdoss]

I've got an older Rheem natural gas forced air furnace.
This winter we've noticed that sometimes, not every time, but sometimes after it's run it's heating cycle and shut off, a couple minutes later the blower comes on for a minute or so.
I know that this is a safety feature, and that it thinks the heat exchanger is still too hot, so it runs to cool it off.
But why would it start doing that this winter?
It maybe does it one out of 6 or 7 cycles. Seems random.

Any ideas or things to check?
The only thing that is different is I put a new filter in a couple months ago and it's a different brand I've never used, and it's supposed to be on of those kind that removes 99.999999999999% of the particulates, but I always use those kind of filters, just not this brand...

Thanks.

Yeah there are millions of ideas for this. Which one do you need?

 

[Rockhead261]

Dude, your fan/limit control is operating as designed. If it's really bothering you that much and you want to keep the restrictive filter, all you need to do is lower your drop-out temperature in 5 degree increments until it doesn't start up again. Personally, I'd leave it alone and put in a fiberglass filter.

Seriously, don't start replacing parts.

 

[Bminder]

Dude, your fan/limit control is operating as designed. If it's really bothering you that much and you want to keep the restrictive filter, all you need to do is lower your drop-out temperature in 5 degree increments until it doesn't start up again. Personally, I'd leave it alone and put in a fiberglass filter.

Seriously, don't start replacing parts.

I know, Rockhead, but this is the first winter it's done like this and I was wondering if I need to check or clean or fix something. I put a basic filter in so we'll see if that changes anything.

 

[Rockhead261]

I put a basic filter in so we'll see if that changes anything.

[emoji106]

Please post the results after a week or so.

 

[LS6 Tommy]

I'm on board with the fan/limit starting to go bad...

Tommy

 

[dreasoner]

I would be on board to consider replacing the entire furnace and not just the limit. The furnace is close to 30 years old. Let the bashing begin.

 

[zmaxmotorsports]

I would be on board to consider replacing the entire furnace and not just the limit. The furnace is close to 30 years old. Let the bashing begin.

Id check the heat exchanger before making that call,a new 8" limit switch is $75.00.
A new furnace is a little more than that.

 

[Showkey]

But the savings of the fuel going up the chimney would be a good off set.
If this is not DIY project then any money spent on this unit needs to be well thought out.

I am on board with the fan limit too........but only after the new filter is replaced with an old style. ( if it's not been done, restricted air flow could be the cause, did not go back reread all the posts) With a little skill and knowledge one could tweak the fan off settings.

 

[zmaxmotorsports]

Sometimes a heavy hand tweaking 30 year old parts can lead to bigger issues ,

 

[TractorJeff]

I have the same vintage Rheem. I run a pleated filter because the house was dusty and filthy when we moved in. Heating bill was $500 a month! I went up there and found the fan and belt were barely turning. Tightened it up and still the temperature recovery was WAY TOO LONG! Had a second furnace to heat the downstairs as the furnace I am referring to is in an attic space adjacent to the 3rd floor bedrooms. Downstairs furnace was replaced with a 95% eff 100btu furnace which will not keep up in a COLD Wisconsin winter. I had taken the 4 speed fan out of the old Rheem downstairs and the limit switches along with the temperature switch before they took it out. I put the 4 speed fan in, set it to run on speed 2. Its a little louder but it moves air across the cast iron heat exchanger better (IMO). Ended up spending that winter having to go up there to tap on the Temperature switch because it was shot. In the early spring I replaced the temperature switch with the one from the other furnace. It will double cycle like yours BUT at the efficiency that those old furnaces run at. I figure it is sucking every last bit of heat it can out of the heat exchange instead of letting it go up the chimney! IMO
Would I necessarily worry about yours double cycling as pending doom?
I don't know in your case, but I know my heating bill has gone down to $300 a month!
That high efficiency furnace downstairs blows lots of lukewarm air but nothing that tells me it is the best deal in the world!

 

[Rockhead261]

Update?

 

[Stevie-Ray]

You haven't replaced your thermostat recently, have you?

 

[mygarageone]

That should be the old style furnace if its an 86-87,Ive never had issues with the standard pleated filters causing a restriction in them.
Anyway if the filter wasnt restricting anything Id probably pull the limit switch out and replace it.
Youll need to pull it out and measure the length of the shaft to get the right replacement for it.
take a picture of the wiring so you can hook it back up the same,and check to see if the jumper has been removed in the bottom so you can do the same to new one.

All he really needs is the number and it should tell the length , it's most likely a Honeywell unit and there part # indicates it's length.

 

[zmaxmotorsports]

All he really needs is the number and it should tell the length , it's most likely a Honeywell unit and there part # indicates it's length.

Its an 8" limit according to my supplier,Around $75.00.

 

[Bminder]

Hey guys, and update:
When I opened it up to replace that hi-efficiency filter, the spring/rod that holds the filter against the side had popped off and the filter was laying loose.
Anyhow, I put a more generic pleated filter in.
It hasn't done it's double cycle trick since even before I replaced the filter.
So for now it's back to normal.
Thanks for all your input!

 

[Chris Stapley]

If it happens again,how about this question,do you also have an a coil for air conditioning? If so,animals in the house too? Check to see that the coil isn't plugged,this too will cause a very hot running unit!

 

[Bminder]

No A/C coil.