Gas Furnace Unexpectedly Turns Off

[Radu Tenenbaum]

Hi,

I had a new 90% efficiency Heil forced air gas furnace installed this past summer. I find that, even when the house thermostat is below the target temperature, the furnace turns off after some time (10-30 minutes), stays off for some minutes, and then turns back on. This goes on until the temperature reaches the target value. Its effects are particularly noticeable with the cold weather we've been having in the Northeast as it takes the house a long time to heat up.

I've done some google searches, and the best theory I've found is that the combustion chamber is overheating and that a temperature limit switch kicks in. This may be because the overheat is real, or because there's a faulty switch. If the overheat is real, it could be caused by insufficient airflow, possibly caused by a dirty air filter.

One time, the burner turned off while I was watching through view port. It attempted to relight three times and then it stopped. I them recycled the main switch and it once again tried to relight without success. Repeated several times in quick succession, with same result. Then, I waited several minutes, and recycled again. This time the burner lit, but the furnace stayed on for only several minutes. This really seems to validate the sensed overheat condition.

I've checked the air filter, and it seems OK. Can I run the furnace for a while without any filter to see if the condition improves? I assume that a filter, even when clean, will restrict airflow.

Any other theories or suggestions? Maybe this is normal for this type of furnace? The installer has been to the house twice and hasn't really fixed this.

On a slightly different topic, I have a question about thermostat management. My wife and I both work and we like cool temperature for sleeping. We program the thermostat to 60 deg F at 10:30 at night and to 72 deg F @ 2:00 pm so the house is warm when we get home at 5:30. Our house is not that tight. BTW, we live in Worcester, MA. Is this too wide a swing? Can anyone point me to a site that explains how to manage the temperature to achieve optimum efficiency?

Thanks,

Radu

[Henry77]

I presume that this furnace was installed by a contractor -right? If so then it should be under warranty so call the contractor and they will come out and fix it and there should be no charge as it should be covered. However if you installed it yourself or had a buddy install it "who knows something about furnaces" (this could be considered "the installer" you mentioned) then I am afraid you SOL as there is effectively no warranty. If it is contractor installed and the guy coming to your house can't fix it I would insist on another tech.

[Steve Scott]

Call the contractor that installed it. You most likely have a minimum

1 year warranty. >Hi,

[kjpro]

Model # Serial #

Do *not* run with no filter.

[Radu Tenenbaum]

The model number is N9MP2100F14A3 manufactured by International Comfort Product Corp.

I am having the installation company continue to address this issue, but I have some curiosity on this matter and would like to be better informed when I talked to the service tech. In a conversation I had with him afte my posting, he dismissed my high temperature shut-off theory. He told me that the temperature override switch on this model can only be reset manually by pushing a button on the circuit board - it does not automatically reset when the temperatue drops.

He maintains that the problem can be caused by only two things: the gas valve, or the ignition mechanism (i'm not using the right terms). He plans to come on Monday and replace the ignition mechanism, and then if that doesn't fix it, he'll replace the gas valve.

Radu

[kjpro]

Yes, know the series very well.

Has he checked the temp rise on the furnace? (if not, he can *not* rule this out!!)

reset manually by

BULLSHIT!! Complete BS!

He better look again, cause he's wrong.

Sounds like a parts changer to me, try this.......then that.

Got some pictures of the install? Post them somewhere, then post a link here to them. When you take some pictures, take one of the drain assemble to.

When the furnace acts up, what's the green light on the valve flashing? (count the flashes.....it will keep repeating it with a pause between)

What's the supply duct measure? What's the return duct measure?

How many supply registers are there? What size & type of air filter are you useing?

[modervador]

temperature, the furnace turns off after some time (10-30 minutes), stays off for some minutes, and then turns back on. >>

OK problem is it cuts out after it is already lit for a while, so first thing we'll replace is the ignition.

This seem rational?

%mod%

[Radu Tenenbaum]

Kjpro,

See pictures at

.

The supply duct on top of the furnace is 20x20 The return duct on the side of the furnace (where the filter is) is 18x22 The filter is a fiberglass mesh type, about 3/4" thick, no frame, and is clean. There are 15 supply registers. Three of them are turned off. The ones upstairs have very weak flow, but that problem existed with the old furnace as well and is another problem.

While I was taking pictures, the flame went out. It tried to restart three times. The first two times, the ignition glowed, the pilot came on and the main burers failed to start. The third time, the ignition glowed but the pilot failed to come on. The light on the valve flashed the heartbeat (I found the flash rate description in the install manual). I tried to recycle the main switch, but no joy. Went upstairs to discover the temperature had reached the thermostat target. I do find it strange that it would try to restart (and fail) even though the shut-down was commanded by the thermostat.

I'll continue to monitor, and if I catch an unexpected shutdown will send the flash data on the valve lamp. Unfortunately, the weather has warmed up so I don't expect the furnace to have long 'on' cycles.

I appreciate your assistance.

Radu

[Radu Tenenbaum]

I questioned him on that, and he told me that the ignition module is interlocked with the flame sensor, so that it can possibly turn off the burner if it is intermittently faulty.

I'm not convinced, which is one reason I posted to this newsgroup.

While all the costs are covered by warrantee, I'd just as soon have this resolved in one visit.

Radu

[Noon-Air]

not enough return air

[Noon-Air]

The problem is not enough return air.... filter is less than half the size it needs to be

[Radu Tenenbaum]

1. How can you tell there's not enough return air? Is the 18x22 dimension of the return air duct too small?

1. Why would this condition cause unexpected shut-down? Is it the overheat situation I described in my original post?

2. How can this be fixed?

Radu

[kjpro]

Not necessarily, the 18 x 22 is more than adaquite as long as the rest of the return can supply it with enough air.

There are several issues with this installation. (I will post them in a reply to the OP above)

[kjpro]

Using the "hog hair" filter I think he's using, it should work with-in limits.

I personnally would like to see a 20 x 25 filter, that way he could use a pleated filter.

But, optimally he'd be better of with a media type filter.

(I will post the list of problems later tonight) (it will be a few things, all install problems)

[Noon-Air]

not for 100,000btu

[Noon-Air]

Check you local code books.... what is the *minimum* return air requirement??? check the manufacturers instructions for the unit.....what is the minimum required return for the furnace??

What is the temp rise??? What does the manufacturer call for??

proper installation and set-up

[Radu Tenenbaum]

It's a 1400 CFM Furnace. What is the conversion factor to BTU's?

Radu

[kjpro]

No, not when that igniter/sensor assembly has about a 1% failure rate.

[CBhvac]

Yup..and the entire senario is screaming overheating condition...and I believe everyones already stated that.... IF its firing, and running, its NOT the ignition. And if its staying off more than 5 minutes, and less than one hour, its not the gas valve or ICB. IF it was, it would go into lockout and stay there for...IIRC 2 hours...have to double check that time, but thats whats coming to mind.

[Steve Scott]