HVAC guys, pilot keeps going out on heater - Chevelle Tech
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post #1 of 17 (permalink) Old Jan 13th, 09, 11:05 AM Thread Starter
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Vinny Vince
 
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HVAC guys, pilot keeps going out on heater

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.

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post #2 of 17 (permalink) Old Jan 13th, 09, 11:46 AM
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Re: HVAC guys, pilot keeps going out on heater

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?
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post #3 of 17 (permalink) Old Jan 13th, 09, 11:51 AM
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Re: HVAC guys, pilot keeps going out on heater

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

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post #4 of 17 (permalink) Old Jan 13th, 09, 11:57 AM
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Re: HVAC guys, pilot keeps going out on heater

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.

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post #5 of 17 (permalink) Old Jan 13th, 09, 12:21 PM
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Re: HVAC guys, pilot keeps going out on heater

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.
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post #6 of 17 (permalink) Old Jan 13th, 09, 3:39 PM Thread Starter
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Re: HVAC guys, pilot keeps going out on heater

Quote:
Originally Posted by Dean View Post
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?

Quote:
Originally Posted by ktrim View Post
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

Quote:
Originally Posted by Dean View Post
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.

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post #7 of 17 (permalink) Old Jan 13th, 09, 5:46 PM
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Re: HVAC guys, pilot keeps going out on heater

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.

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post #8 of 17 (permalink) Old Jan 13th, 09, 7:24 PM
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Re: HVAC guys, pilot keeps going out on heater

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.

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post #9 of 17 (permalink) Old Jan 13th, 09, 7:30 PM
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Re: HVAC guys, pilot keeps going out on heater

Quote:
Originally Posted by MrBill66Malibu View Post
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.

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post #10 of 17 (permalink) Old Jan 13th, 09, 7:43 PM
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Re: HVAC guys, pilot keeps going out on heater

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.

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post #11 of 17 (permalink) Old Jan 13th, 09, 7:50 PM
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Re: HVAC guys, pilot keeps going out on heater

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.

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post #12 of 17 (permalink) Old Jan 13th, 09, 8:30 PM
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Re: HVAC guys, pilot keeps going out on heater

Quote:
Originally Posted by 17Again View Post
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.

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post #13 of 17 (permalink) Old Jan 13th, 09, 8:55 PM Thread Starter
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Re: HVAC guys, pilot keeps going out on heater

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?

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post #14 of 17 (permalink) Old Jan 13th, 09, 9:06 PM
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Re: HVAC guys, pilot keeps going out on heater

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

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post #15 of 17 (permalink) Old Jan 13th, 09, 9:20 PM
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Re: HVAC guys, pilot keeps going out on heater

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.

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