Furnace or Electrical Problem?

[Andrew Joiner]

I turn our thermostat down to 60F every night. It's the old Honeywell mercury bulb type. We have a 10 year old 90% efficient gas furnace.

For the the past 2 days when I turn the thermostat up to 66F in the morning the furnace won't start. The room temp is at 56F on the thermostat. It usually starts within a few seconds in this situation. I wait awhile thinking "doesn't it normally fire up by now?". Then it's 10 steps out to the garage to check the breaker. The circuit breaker isn't tripped but I flip it anyhow and in 5 seconds the furnace starts. It runs and heats fine, but it's 2 days in a row now and I'm concerned.

Is it just a coincidence, that flipping the breaker off and on the last 2 days did the trick?

It's been 20F colder than usual for 2 days. Could that have anything to do with this?

Thanks in advance for any help.

[Steve Schlumpf]

Andrew - I have close to the same setup other than I changed out our mercury switch for a digital one a few years back and it was worth it!

On your problem... when was the last time you changed out the thermal coupling? I have to change mine every 3 to 5 years .

[George Bokros]

How does the furnace behave during the day? Does your furnace have pilot light, I doubt it. If it does not have a pilot light it likely does not have a thermocouple. I just replaced my 14 yo furnace and it did not have pilot light. It had an electronic igniter and a electric eye to monitor the ignition of the burner.

I have no idea why flipping the breaker causes the furnace to come on. If the furnace operates fine during the day then I would not suspect the thermostat but if could be malfunctioning because of the colder temp in the house at night perhaps.

George

[Rich Engelhardt]

I changed out our mercury switch for a digital one a few years back and it was worth it!Programmable thermostats are dirt cheap these days and well worth the few dollars they run.
Re: the thermal couple - buy two. Use one and hang the other next to the furnace. I can almost guarantee that a thermal couple will pick the coldest Sunday night of the year to go bad.....or..a holiday when all the stores are closed...
Pick up one for the water heater while you're at it. They go bad when you have a whole house full of in laws over.....
Those little buggers have a real nasty disposition and they're smarter than all get out. <-- the thermal couples that is. It's usually only half right as far as the in laws are concerned & that depends a whole lot on which in laws it is....



It's been 20F colder than usual for 2 days. Could that have anything to do with this? I'm no furnace guy, but, that doesn't sound abnormal w/that much of a temperature difference. I believe the furnace has to come up to a certain temperature before the fan kicks on. If the furnace is drawing fresh air from the outside, that may account for the delay.

[Andrew Joiner]

I'm no furnace guy, but, that doesn't sound abnormal w/that much of a temperature difference. I believe the furnace has to come up to a certain temperature before the fan kicks on. If the furnace is drawing fresh air from the outside, that may account for the delay.

Rich you may be on to something, as it is a direct vent style that draws out side air in and exhausts combustion out thru PVC pipes. It may happen with every (rare) cold period we get and I just don't notice.

I don't see a thermocouple on the parts list. It's got an electronic igniter and flame sensor.

[Jerome Stanek]

My daughters furnace would not always start i had to clean the heat sensor and now it fires up and stays lit

[Shawn Siegrist]

It sounds like your having an electrical issue, when you flip the breaker off and then on your resetting what ever fault is happening. If it happens again before you flip the breaker check your furnace, mine has a indicator light that flashes red when there is a fault.

good luck!

[Stephen Tashiro]

The circuit breaker isn't tripped but I flip it anyhow and in 5 seconds the furnace starts..

If the furnace control system interrupts the operation of the furnace, your flipping of the breaker is reseting the system, so it isn't surprising that the furnace will start.

I have a Carrier "Weathermaker" high efficiently furnace that is over 10 years old and your problem sounds familiar. The main problems with my furnace involves the fact that it must drain water and something in the drain system will get clogged. This interrupts the vacuum line that senses if the furnace motor is pulling air into the combustion chamber and that causes a vacuum operated switch not to open. In the early stages of this problem, the furnace starts normally but shuts off prematurely. It does not automatically restart. In this stage, cutting the power off and on will let the furnace restart. In the later stages of the problem, the pilot will not even light. The furnace turns on but I never hear the loud click of the vacuum operated switch opening to let gas through.

Working from the end of the drainage system upward, at various times I've had to unclog the clear plastic tube and remove and unclog the black plastic cylinder that's upstream from the tube. Recently those measures didn't fix the problem and my trusty service man found that he had to clean out the little hole where one end of the vaccum line connects to the furnace.

[Andrew Joiner]

Thanks for the comments. It's working fine. Probably just a coincidence on the breaker flip.

[Jerome Stanek]

I still would clean the heat sensor. Just a little emery cloth or steel wool and wipe down with clean rag. My daughters looked clean but it had just enough to keep it from working. It would work sometimes but not all the time.

[Andrew Joiner]

The main problems with my furnace involves the fact that it must drain water and something in the drain system will get clogged. This interrupts the vacuum line that senses if the furnace motor is pulling air into the combustion chamber and that causes a vacuum operated switch not to open. In the early stages of this problem, the furnace starts normally but shuts off prematurely.


Yes, this is what it was. I had this problem in the second year I had this furnace. Then the drain pipe was clogged with snow and froze as it exits the building. Since there's no snow it was my last thing to check, but the tube was clogged with something. Blowing out the tube solved the problem.

Thanks for all the feedback.

[Myk Rian]

I still would clean the heat sensor. Just a little emery cloth or steel wool and wipe down with clean rag.
Won't do any good if it doesn't call for flame in the first place.
As mentioned, you're re-booting the furnace, which is clearing the fault. I would call someone in to look at it.

[John Fabre]

My daughters furnace would not always start i had to clean the heat sensor and now it fires up and stays lit


This is so true, it happens on mine every two years.

[Andrew Joiner]

WARNING !

The furnace ran fine for 24 hours after I cleaned the drain tube. I had to fix a crack in the drain line too. The next day no heat. No drain problems, and the flame would light and then go right off. So it must be a dirty flame sensor now.

I was in a hurry because it was near closing time for parts. I checked the drawing in the manual,but saw no flame sensor at the indicated location. I removed the only part sticking down into the flame area with a wire leading to it.

Here's why I say WARNING!!! know the difference between the electronic igniter and flame sensor before you start cleaning with emery or steel wool. I thought boy this thing is dirty. It was like a little loop of cast iron and very brittle. As I was sanding it snapped. After the smoke stopped coming out of my ears I started calling around for parts.

It's been unseasonably cold here so no one was in. A couple places said flame sensors would be at least a day for parts to come. Finally one guy said " It sounds more like the electronic igniter not flame sensor." Good news for parts as electronic igniters are easier to get than a flame sensor. He quoted me $200 and he'd send a guy out tommorrow. I went and looked closer at the furnace and behind a pipe is the flame sensor all caked and dirty. We were ready for night of borrowing electric heaters.

The good news. The phone rang. It's 5 minutes to 5:00 pm. A friendly voice said " do you need an electronic igniter ? I had read a part # earlier to a woman in the office of a repair place, and her service guy Don took the time to find the part before he went home after a busy day. "Yes, I need the igniter Don but when do you close?" Don said" 5:00 but since your 10 minutes away I'll wait for you". When I got there and Don showed me the exact part I needed I almost kissed everyone in the office I was so happy. At this point I was unsure of my patience with furnaces so I asked Don if he'd be willing to work late and install the part and get our furnace running. To my surprise he said yes.
An hour later I'm writing a check for less than half the $200 quoted by his competition. Don was chatting with my wife, turned out he's an old friend of her family. Don would not accept a tip.

Yes, cleaning the flame sensor was the needed fix this time. Don said it was just a coincidence that the drain was plugged and the flame sensor needed to be cleaned as well.

So do not break your electronic igniter thinking it's a flame sensor.

[John Coloccia]

The real lesson here is have your furnace serviced every year, or at LEAST every two. They will replace whatever needs to be replaced (nozzles, whatever), replaced the oil filter, clean whatever needs to be cleaned, and you'll never have an issue like this again.

[Myk Rian]

Pilotless ovens also use those ignitors. 2 of them.
1 for the lower burner, and 1 for the broiler.

[Curt Harms]

Our furnace - mid 90s York gas - used an igniter made of discs in a sort of christmas tree shape. I think the discs were made of some sort of carbide. Apply not that much current and they'd glow. They'd also fail routinely. The last replacement was a nichrome wire loop type igniter - same mount - and it's been fine for years. Of course now that I said this, I better have a spare on hand :p.