: HVAC guys, pilot keeps going out on heater


69-CHVL
Jan 13th, 09, 11:05 AM
Having a problem with the heater at my rental prop, forced air gas heater pilot keeps going out. It will stay on for a couple of days, but then go out. I changed thermocouple out 2x, still does it. Called in some clown, changed gas valve, still does it. Called another expert, reset the position of the pilot/orifice/etc, still does it. I changed the gas valve out a month ago myself again, pilot went out again.

Question I have is, is there anything in the system that can shut the pilot off? I figure it should stay on no matter what right, so long as gas is coming into the home. T-stat is new too, but I didnt think that mattered. I afraid if I replace the entire unit, it may do it again b/c of something I'm overlooking.

Dean
Jan 13th, 09, 11:46 AM
Does it have an Energy Cut Ooff ?
There are a lot of causes for a pilot outage problem.
Might have a crack in the heat exchanger or a smothering problem due to a stopped up or restricted heat exchanger or flue exhaust.
Have plenty of make up air?

ktrim
Jan 13th, 09, 11:51 AM
has anyone cleaned out the feed tube to the pilot light? Ran in to this with my furnace- Had some dust and lint partially blocking the tube- cleaned it out and alls good

rubadub
Jan 13th, 09, 11:57 AM
I just put a new gas valve in my natural gas boiler, pilot light kept going out, screwed with it several times, then put in another gas valve, problem gone, the new gas valve was faulty.

It looks like its a hit and miss with these new gas valves.

Dean
Jan 13th, 09, 12:21 PM
Another thing (which I'm sure the two techs already checked) is, the thermocouple depends on having it's top 5/8" bathed by a nice blue flame AND the rest of it relatively cool.
Getting too hot @ it's "cold junction" will lower it's millivolt output greatly.

A thermocouple should put out around 30 MV with no load but somewhere around 12-13 MV under load.
I check the millivolts under load while observing the furnace operation.

69-CHVL
Jan 13th, 09, 3:39 PM
Does it have an Energy Cut Ooff ?
There are a lot of causes for a pilot outage problem.
Might have a crack in the heat exchanger or a smothering problem due to a stopped up or restricted heat exchanger or flue exhaust.
Have plenty of make up air?


Dean, not sure what a ECO is, but this is probably a 20 yr old heater, made by Heil. I was thinking about the HE, but how would a crack affect the pilot? Not sure about the make-up air - what's that?

has anyone cleaned out the feed tube to the pilot light? Ran in to this with my furnace- Had some dust and lint partially blocking the tube- cleaned it out and alls good

yeah we replaced the feed tube and orifice, 2x

Another thing (which I'm sure the two techs already checked) is, the thermocouple depends on having it's top 5/8" bathed by a nice blue flame AND the rest of it relatively cool.
Getting too hot @ it's "cold junction" will lower it's millivolt output greatly.

A thermocouple should put out around 30 MV with no load but somewhere around 12-13 MV under load.
I check the millivolts under load while observing the furnace operation.

Dean, I was just checking out the pilot, the tip of it ~5/8" it enguphled in a blue flame, and its like a little blow-torch, hard to blow out even.

One thing that I dont like though is the thermocouple tip is touching the metal of the HE, bet that could cause a stray voltage or affect the heating of it.

MrBill66Malibu
Jan 13th, 09, 5:46 PM
You need to check the incoming gas pressure. If it is under 5 inches of w.c. raise it to 7 and reset the burner manifold pressure to name plate specs, usually 3 inch w.c.

I had this problem many times, when everyone in the area were using their furnaces I would see pressures drop below 3 inches, then the city started converting to a higher pressure supply system.

But your incoming pressure needs to be checked.

17Again
Jan 13th, 09, 7:24 PM
Hard to believe multiple gas valves and thermocouples are bad.
#1 did they inspect the heat exchanger for cracks, very important! Cracks in the heat exchanger allow the blower to actually blow out the pilot, or draw carbon monoxide into the space which can kill. At 20 years old you are really running some risks with others lives, have this furnace properly inspected.
#2 20 year old furnace is the flue pipe still properly in place with the proper flue cap on the roof. High winds can cause the problem you are refering to, especially if the flue cap has somehow blown off.
#3 There is a possibility that the vent on the gas regulator at the meter is plugged or restricted, dirt, snow, spider nests they all cause it.

17Again
Jan 13th, 09, 7:30 PM
You need to check the incoming gas pressure. If it is under 5 inches of w.c. raise it to 7 and reset the burner manifold pressure to name plate specs, usually 3 inch w.c.

I had this problem many times, when everyone in the area were using their furnaces I would see pressures drop below 3 inches, then the city started converting to a higher pressure supply system.

But your incoming pressure needs to be checked.

All due respect Bill, but checking gas pressure should be left to someone with the tools and experience. Curious though as to why a service guy would flat out replace a gas valve new or old without checking gas pressure on the outlet and pilot of the valve.

66SSFan
Jan 13th, 09, 7:43 PM
Rob has some great points here. When you do get it running, buy a C.O. detector and plug it in anywhere in the house for saftey. Don't worry about this being an issue with a replacement furnace as the several styles of pilot light assemblies have been replaced by hot surface ignitors in most all quality furnances. It is a strange issue your having, the main gas pressure when the burners are lit should be 3.5" w.c. but the pilot pressure is adjusted by the flame length and not usually measured for pressure. There should be an inlet screen at the gas valve that acts as a filter, it's not common but I have seen some junk collect there if the county has been doing some work on the gas lines close by. Another thing to check is the length of the thermocouple, it shouldn't be too long. It's ok to have it coiled up a couple times but shouldn't be coiled a bunch, even thought the pressure in the line shouldn't drop it can cause some problems.

Gene McGill
Jan 13th, 09, 7:50 PM
I had a similar problem on a hot water heater; pilot would go out for no apparent reason. It ended up being corrosion on the inside of the flex tube between the gas valve and hot water heater. I could hardly blow through it, and was suprised that it worked well enough (most of the time) to heat water, much less keep the pilot lit.

MrBill66Malibu
Jan 13th, 09, 8:30 PM
All due respect Bill, but checking gas pressure should be left to someone with the tools and experience. Curious though as to why a service guy would flat out replace a gas valve new or old without checking gas pressure on the outlet and pilot of the valve.

Sorry about that, I should have written that "he needs to have it checked". Yes, most Techs will check outlet pressure of the valve, but very few check incoming pressure. :)

69-CHVL
Jan 13th, 09, 8:55 PM
One of the techs that I had over did check the pressure, said it was OK, dont remember the exact # though. I have another co coming out tomorrow.

My biggest fear is replacing this for 2000.00 and it will do it again. If I cant blow this out by mouth, how could a cracked HE or venting do it?

17Again
Jan 13th, 09, 9:06 PM
Vince,
By bringing in a new company every time you are reducing the chance to actually solve the problem. Each new person will come to the same conclusion the previous one did. I know my shop in dealing with an ongoing issue and callbacks will actually give the customer a break in the service call fees just to ensure customer satisfaction. We aren't gods and do make mistakes and miss the obvious sometimes. As far as $2k and the same issues, the furnace shouldn't have to be replaced unless the heat exchanger is cracked.
Simple test, with the pilot lit turn on the summer fan switch at the thermostat, and compare the flame movement of the pilot. Is it waving excessively? Turning Orange instead of blue? Can you feel air blowing around the burners?
Has anyone looked at the roof to see if there is a flue cap still in place? Has there been high winds recently (or during pilot flame failures)?
Rob

Randy Mosier
Jan 13th, 09, 9:20 PM
I see the flu cap was mentioned as a possiblilty. I've had a similar issue with my water heater. It happens when the wind is blowing and gusting. A twenty year old system will also have a twenty year old ventilation pipe going to the roof. I would make absolutley certain that pipe and the cap are in good shape, even if another problem is found that's causing the pilot light issue. That vent pipe removes carbon monoxide from the work/living area and it's vital that it be in sound condition.

The Deejay
Jan 13th, 09, 11:44 PM
A coupla suggestions...i sold Heil and Whirlpool equipment for quite a few years...if yours is twenty years old, i can almost guarantee you have a cracked combustion chamber...not just these brands, but everyones hard pressed to last that long....as others have stated, this problem will usually blow out the pilot...i would strongly urge you to buy a carbon monoxide detector ASAP and plug in .....it might go off immediately.. if so carbon monoxide is at dangerous levels..it's odorless, colorless, tasteless, but most of all, lethal.Several good brands out there, i sell Kidde brand carbon monoxide and smoke detectors to HVAC contractors....secondly, if your exhaust pipe from furnace is single wall, it may have rusted into or have cracked, allowing insufficient venting, or if vent cap is stopped up with leaves, bird nest or what ever, this will also cause carbon monoxide problems...you won't go to bed with your Chevelle idling in your garage.....don't go to bed with your furnace also putting out carbon monoxide in you home..not trying to scare you, but people alll the time during the winter go to sleep and never wake up from faulty gas appliances....we all want you to be here on this forum for a long time:yes:

Dean
Jan 14th, 09, 12:09 AM
The thermocouple should definitely NOT be touching the heat exchanger.
That very well could be the problem right there.

An ECO is a temperature sensing switch that breaks the circuit of the thermocouple and drops out the magnet in the gas valve, shutting everything off.

Usually a couple of wires can be seen where the thermocouple screws into the magnet on the gas valve.