Gas furnace - pilot light issue

[normstad]

Couldn't light the pilot light, so replaced the thermocoupler. Great, pilot light goes on, furnace lights, and all is roses, right?

Not quite. It seems that the furnace works, but one it reaches temperature, and shuts off, the pilot light goes out also. I have no problem re-lightening it, and the main flues fire up again, but it will not cycle.

Anyone have experience with this type of problem? The furnace is an older Anthes model.

[TylerThomson]

What colour is your pilot light flame?

[trophybook]

Hi temp limit switch may be pooched

[normstad]

What colour is your pilot light flame?

Nice blue color.

[TylerThomson]

K its not that then. A yellow flame indicates poor air flow or soot build up. When you installed the new thermocouple did anything get bent? If the flame isn't on the end of the thermocouple it may not be getting hot enough.

[normstad]

Hi temp limit switch may be pooched

The blower fan turns off, and the furnace itself will light, at least the first time. Would it if the limit switch was pooched?

[normstad]

K its not that then. A yellow flame indicates poor air flow or soot build up. When you installed the new thermocouple did anything get bent? If the flame isn't on the end of the thermocouple it may not be getting hot enough.

Yeah, I thought of that. The flame is primarily on the main body of the thermocouple, not on the tip. In other words, it is on the most exposed part. It was my understanding by only being on the tip, the thermocouple will not work properly.

[TylerThomson]

The tip should be in the flame along with about another 1/4 to half inch of the thermocouple

[normstad]

The tip should be in the flame along with about another 1/4 to half inch of the thermocouple

Hmmm... I may have to adjust that then. Project for the morning.

[Stubb]

This happened to me last month and it turned out the screen in the bottom of the tank was plugged and not letting sufficient air in to satisfy the pilot. It would stay on until the main burner shut off then it would slowly die out.

[TylerThomson]

If his flame is blue and not yellow it should have sufficient air but still worth a look.

[CaberTosser]

There are instances where the issue is not the thermocouple or pilot light, though they are the best spot to start. As noted the flame needs to be burning clean (blue, not yellow) and the impingement over the end of the thermocouple is important. If all that is the case and the pilot light still drops out it can often be a problem within the gas control valve, the thermocouple powers a 'power unit' which is a millivolt electromagnetic plunger that is always trying to shut, sometimes that component becomes power hungry due to shorted windings in it and then you'll need a gasfitter to replace the entire gas control valve. I performed such a call for an AO member just last week.


This happened to me last month and it turned out the screen in the bottom of the tank was plugged and not letting sufficient air in to satisfy the pilot. It would stay on until the main burner shut off then it would slowly die out.

This sounds a bit off, how could the pilot light possibly starve for air after the main burner shut off if there was enough air available for the main burner to fire in the first place? If there's not enough air for the pilot light then no way in heck is there enough air for the main burner......

[Weedy1]

The tip should be in the flame along with about another 1/4 to half inch of the thermocouple

Good point, just throwing this out there without being able to see what's going on BUT as a minimal precaution, have a Co monitor, check for a cracked heat exchanger blowing pilot out. You can start a pilot flame with a lighter/match, then the burner comes on then, the burner turns off and the pilot flame is blown out by air from a cracked heat exchanger. Hate to see a guy gassed to death.

[normstad]

There are instances where the issue is not the thermocouple or pilot light, though they are the best spot to start. As noted the flame needs to be burning clean (blue, not yellow) and the impingement over the end of the thermocouple is important. If all that is the case and the pilot light still drops out it can often be a problem within the gas control valve, the thermocouple powers a 'power unit' which is a millivolt electromagnetic plunger that is always trying to shut, sometimes that component becomes power hungry due to shorted windings in it and then you'll need a gasfitter to replace the entire gas control valve. I performed such a call for an AO member just last week.


Sounds like my first step is to adjust the thermocouple. I'll report back tomorrow if it worked, or not.

[Weedy1]

There are instances where the issue is not the thermocouple or pilot light, though they are the best spot to start. As noted the flame needs to be burning clean (blue, not yellow) and the impingement over the end of the thermocouple is important. If all that is the case and the pilot light still drops out it can often be a problem within the gas control valve, the thermocouple powers a 'power unit' which is a millivolt electromagnetic plunger that is always trying to shut, sometimes that component becomes power hungry due to shorted windings in it and then you'll need a gasfitter to replace the entire gas control valve. I performed such a call for an AO member just last week.




This sounds a bit off, how could the pilot light possibly starve for air after the main burner shut off if there was enough air available for the main burner to fire in the first place? If there's not enough air for the pilot light then no way in heck is there enough air for the main burner......

If I were to internet diagnose I'd go with this ^^^^ The problem is when it comes to gas and CO I have to do so with an extreme amount of caution. Sounds like we're dealing with an old standing pilot similar to the old Flame Masters. I need not say no more.

[Stubb]

There are instances where the issue is not the thermocouple or pilot light, though they are the best spot to start. As noted the flame needs to be burning clean (blue, not yellow) and the impingement over the end of the thermocouple is important. If all that is the case and the pilot light still drops out it can often be a problem within the gas control valve, the thermocouple powers a 'power unit' which is a millivolt electromagnetic plunger that is always trying to shut, sometimes that component becomes power hungry due to shorted windings in it and then you'll need a gasfitter to replace the entire gas control valve. I performed such a call for an AO member just last week.




This sounds a bit off, how could the pilot light possibly starve for air after the main burner shut off if there was enough air available for the main burner to fire in the first place? If there's not enough air for the pilot light then no way in heck is there enough air for the main burner......

I thought the same thing but figured maybe the larger flame created a stronger pull that maybe temporarily moved some of the debris on the screen in order to get air. Could be totally out to lunch but just sharing my recent experience on the same issue.

[Weedy1]

I thought the same thing but figured maybe the larger flame created a stronger pull that maybe temporarily moved some of the debris on the screen in order to get air. Could be totally out to lunch but just sharing my recent experience on the same issue.

What screen are you talking about?

[Stubb]

There's a screen in that combustion area that allows air in to feed the flame. My tank was about 10 years old and over the years dust and scale from the burner had covered it. You should be able just to vacuum it while the front "door" is off.

[Weedy1]

There's a screen in that combustion area that allows air in to feed the flame. My tank was about 10 years old and over the years dust and scale from the burner had covered it. You should be able just to vacuum it while the front "door" is off.

He has a standing pilot system, that screen wouldn't be there. He's talking about a furnace also.:)

[TylerThomson]

I'm going to bow out of this one as cabertosser is obviously more experienced in this area. Well that and I'd be out of ideas after my last suggestion haha

[Kim473]

How old is this furnace ? Is it time to replace to a newer more efficient one ?

[Unregistered user]

Pilot light flame big enough? When you changed the thermocouple, the connection was clean and tight?

[dewalt18]

How old is this furnace ? Is it time to replace to a newer more efficient one ?

I want to say that somewhere around '88ish is when "mid" efficient furnaces became the norm in Alberta, so with the OP having a pilot light issue, God furnace was likely installed before then.

With the average life of a furnace ranging in the 15-20 year park, I would say that it's probably getting close the the end of its time. . .

I could also be wrong about everything! Lol

[CanuckShooter]

Pilot light flame big enough? When you changed the thermocouple, the connection was clean and tight?

The pilot light should also be really throwing a strong flame. The additives they put in propane can clog orifices over time, this happened with mine, a soaking in gasoline usually cleans ups the contamination.

My latest issue is similar to the OP. The pilot lights, and the burner lights, but I have no temperature adjustment [it ran every night for a week like this]. When I got it home from our deer hunt I started it up so all our canned stuff wouldn't freeze up, and it went out [like the op] a few times in the first few hours of lighting it. I suspect it's the gas controller that is causing the issues.

[dewalt18]

After reading the original post, I'm thinking maybe you should take a look at your filter. Not all, but some furnaces will have an interlock between the high limit and the gas valve. If your filter is clogged up, it will run until the furnace over heats, with you thinking it was a full cycle, but will go into safe mode, disabling heating function. Just a thought. Would have to see it run in person to do a proper diagnoses.

[Stubb]

He has a standing pilot system, that screen wouldn't be there. He's talking about a furnace also.:)

Oops. My bad

[acrtech]

Normstad hasn't came back with his results yet, but in the OP.., it states that pilot has been lit and the main burners fire.., when main burner goes out, it takes the pilot with it, and says that there is concern about it not cycling.
First, the Pilot may not be strong enough allowing it to snuff out main main burner extinguishes,,
by not cycling, does the OP, mean the fan motor does not come on? then confirm power to the motor first then, belt, pulley and would have to look at the fan controller - controlling the "on Fan" this could be the type that works on temp in the cabinet or a sequencer type that has its own heaters that would bring on the fan after it reaches a certain time limit...say 50-90 sec.

Anthes furnaces date back to the early 70"s

[kevinhits]

I want to say that somewhere around '88ish is when "mid" efficient furnaces became the norm in Alberta, so with the OP having a pilot light issue, God furnace was likely installed before then.

With the average life of a furnace ranging in the 15-20 year park, I would say that it's probably getting close the the end of its time. . .

I could also be wrong about everything! Lol

Would you believe that I bought a bungalow in Dover (Calgary) that was built in 1972 in 1997...I lived in this house till 2002 and got married. I kept this place as a rental house till 2011 when I sold it. Still the original work horse furnace was still in it....I greased, changed fan belts and maintained it all along...LOL.....29 years:)...The only complaint I had was it ran loud:bad_boys_20:

[brslk]

My old garage had a furnace in it from 1970. It was there and working right up until we tore down the house and garage a few years ago.
My nephew removed it before we knocked down the place and put it in his garage where it still keeps his cars nice and toasty.
The only thing I ever had to have done with it was a gas valve thingy (I know nothing about furnaces) had to be changed. I think it was around $200 in 2010.
1970... A good year for furnaces and people to be made!

[Ricki Bobby]

Control valve

[Nate_K1500]

Hi temp limit switch may be pooched

This is exactly what is happening ^^
its not sending the signal to your blower to tell it to turn on and start pushing the hot air into the house. So now it keeps getting hotter and hotter till the high high level sensor tells to shut down before it melts your house down.
Replace the temp switch ($6) and your back in business!!

[dewalt18]

A furnace with a standing pilot will likely have a Honeywell combination switch, which is basically a temperature controlled device that tells the blowers when to turn off, turn on, and controls the high limit safeguard.

If you can buy one of these for $6, buy a bunch because they sell wholesale for about ten times that price. . .

[burnme]

After reading the original post, I'm thinking maybe you should take a look at your filter. Not all, but some furnaces will have an interlock between the high limit and the gas valve. If your filter is clogged up, it will run until the furnace over heats, with you thinking it was a full cycle, but will go into safe mode, disabling heating function. Just a thought. Would have to see it run in person to do a proper diagnoses.

This is exactly what happened to my daughters place last year. Wont even say how bad the filter was.

[normstad]

K its not that then. A yellow flame indicates poor air flow or soot build up. When you installed the new thermocouple did anything get bent? If the flame isn't on the end of the thermocouple it may not be getting hot enough.

Just a follow-up and thanks to all that made suggestions.

Furnace seems to be working fine. I adjusted the thermocouple downwards so the pilot light constantly keeps the heating the tip. I had assumed that as long as the light was on the bulk of the body, that would be fine.

Again, thanks, and sorry for the delay in giving it.