Furnace pilot light won't stay lit

I own a rental house in the next county, about a half hour drive away. The tenant called last night to tell me the pilot light of the furnace won’t stay lit. She described what she had done to try to relight it (following the instructions which are with the furnace), and everything she did was correct.

I installed the furnace last summer during a complete remodel, and the tenant moved in at the end of October and has been using it every day since then. Unfortunately, I bought the furnace last January, so the one year warranty has expired. I’ll call customer service at the manufacturer tomorrow, and maybe they will be able to provide the information I need to take care of the problem. Whether they do or not, I’d be grateful for advice from anyone familiar with furnaces who can suggest what can make a pilot light fail to stay lit---particularly after less than five month’s use in a new furnace---and what I can test for, and what I can do about it.

Stan

Stan,

Is this propane or natural gas? Standing pilot?

Fuel supply first.

Second, perhaps the proof of pilot flame is not registering. Some use the small cylindrical rod with a single wire lead, if so, pull the sensor and rub it with a scotch-brite pad, nothing metallic.

Perhaps the gas valve itself is the problem?

Look at the source of ignition.


Sorry to be so sparse, but I am not there to see for myself...

D.

First thing is the thermal generator. If you have a standing pilot. Tighten the two screws or the 3/8 nut from the thermal generator ,"depends what type of valve" only a TINY bit. DON'T strip stuff!!!!!
Thermal piles or generators are cheap and a lot of box stores and plumbing or hardware stores carry them. In my line of work,commercial cooking equipment, I change a few of these almost weekly. If you have a good digital meter you can mesure the output. A big fat generator should be in the 500+mv range. The small thin ones are in the 250/300mv range.If you DO have a flame sensor type of system get a repair guy in. Don't mess with it. The ignitor box is mostly likely the problem. Good luck.

We call them thermal couplers,you buy them buy length. Too long and you just make a loop and leave it zip tied up. too short and you need a longer one. Easy job. Whenever I had a pilot light furnace, I kept a spare all of the time, should be way less that ten bucks.

I learned quite a while ago to always keep a spare thermocouple on hand, as you don't generally notice you have no heat or hot water until the stores are closed.

If the pilot flame is properly adjusted, a thermocouple will last a very long time. If it's too hot, though, you'll be replacing it every couple of years.

Different furnaces operate differently and most furnaces haven"t had a standing pilot light for 30 years or so. Be more specific. Just a guess: Clear the air intake, if you have one.

1 year warranty on a furnace?

mine did that---a thorough cleaning of the pilot and thermocouple that had soot on them solved the problem

(quoted from post at 21:21:39 03/10/13) I own a rental house in the next county, about a half hour drive away. The tenant called last night to tell me the pilot light of the furnace won’t stay lit.
Stan

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If it is in fact a "standing pilot" furnace it will have a thermocouple and if so, once the pilot is lit it takes several seconds for the millivoltage of electricity to be generated strong enough to hold in the safety coil in the gas valve. So, did she keep the pilot knob or button depressed for maybe 10 seconds before turning loose ? If she did and it still does not stay lit, replace the thermocouple. You'll need a 3/8 7/16 and a long phillips or long 1/4" nutrunner. And a flashlight unless you can see better than I.

If it is not a true standing pilot it will probably be a glow coil with a direct ignition sequence. Meaning the inducer motor will start and first go through a pre-purge sequence, send power to the glow coil ignitor which will cause it to glow bright orange. Then the main valve will open once the feedback tells the circuit the glow coil is energized. The main flame is then ignited by passing a portion of the gas over the hot surface ignitor and if not, the flame rectification circuit in the control board will close the main gas valve and lock out the gas flow. The glow plug also serves as the flame rectification circuit. If its a hot surface ignition type of furnace, chances are the igniter is bad. If it is and you can obtain a replacement, DO NOT touch the ignitor surface of the new one with your fingers as it will cause premature failure.

Most furnaces will allow this to happen three times, then lock out permanently, send a code to the circuit board and power has to be reset to reestablish an attempt again. Then repeat.....

First thing to do on an electronic ignition furnace is to look through the (typically) provided peep hole and see the flashing diode/diodes, count them then look inside the door for the failure codes.

Anything beyond that, you may ought to call a qualified tech.

Good luck. Post back with what you found.....

If you have an ignitor like this one and it is fed 120vac it's probably defective. Use a multi-meter set on ac volts and check at the plug for voltage. If there's voltage present then shutoff ac voltage to the furnace. Switch your meter to ohms & separate the plugs and check for continuity on the ignitor. If there's no continuity replace the ignitor. This one cost about $13.00. Hal

Wow! What a lot of really good, specific, detailed advice. I haven't gone to the house to inspect and try to resolve the problem yet. Probably tomorrow.

Here are my responses to some of the issues which have been raised here:

1. It's a Williams natural gas wall furnace, an exact replacement for the one which had been there since the 1950's. Using a replacement which was virtually identical to the old one made the installation much easier than it could have been. I had never installed a furnace before, so ease of installation was important to me.

2. The renter held down the pilot knob for a full minute---twice as long as the instructions recommended. My guess is that she held it down for 30 seconds the first time she tried it, and when that didn't work, she held it down longer. (She's a great renter, and if I told her I wasn't going to be able to get out to fix the furnace until July, she would probably find some way to deal with it.)

3. Yes, only a one year warranty. That's what the instruction manual said. A different brand of furnace might have come with a longer warranty, or a paid installer might have offered to stand behind it for longer than a year. But I wanted to use this brand and model for the reasons I explained above, and I saved over $1000 (nearer to $2000 compared to the highest bid) by buying and installing it myself.

4. It is a standing pilot model---you light the pilot with a match. I'm glad the renter reminded me of that or I might have gone there without matches. The natural gas freestanding stove I have in my house lights with a piezo-electric striker (I think that's what it's called), and I had gotten it in my mind that the pilot in the furnace in the rental house lit the same way.

Thanks, everyone. I feel much more confident about dealing with this now. I'll post the results when I get some.

Stan

similar but related, I had the same issue with a water heater recently. I was able to test the thermocouple by metering the resist and heating it. I did it and the guy at a professional plumbing supplier did too. The thermocouple was not bad. What was wrong though was the pilot flame itself was too small. I had to take the burner lines etc from control and remove tube to pilot and clean pilot tube and orifice. This orifice is the size of a human hair so just a little bit will reduce flame size. also buffed coupler end with a 3M pad. the worst part was finding very good fitting wrenches to remove the line fittings without rounding off. Years ago pilot flame pressure was adjustable at the valve/control but all that has been factory sealed.

Bit different as this is an unventer wall heater. Think about 6 years old Worked goon for several years then last year started having problems, this year got to where was lighting every hour. Finall got wifr to look up and try to buy new part, no longer in business but did bring up a diagram. One glance at it saw a screw I had missed and service mam last year had missed as well I guess. That screw had let the thermo coupling slide down enough that the pilot could not keep it warm. Raised it so it was back in flame same as others I have and is not going out now. Somight just check if it is still where it is supposed to be or if it sliped before you go replacing parts.

Open the doors and windows for a few minutes. It's possible with a bad furnace to deplete oxygen in an older home if the tenents are not going in and out much. Check th CO in there.

Hi missouri massey man,

I went there this afternoon and confirmed that it was a standing pilot. The renter had used the correct procedure to try to relight the pilot (except that she used a match, and it turned out that it did have a striker type ignition button). I couldn't make it stay lit, either. I removed the thermocouple and cleaned it, and cleaned the pilot assembly with a soft toothbrush. N/G. I brought the thermocouple home with me, and I'll replace it tomorrow.

You mentioned that I'd need several wrenches and a long phillips. Is the long phillips to remove the whole pilot assembly, including the thermocouple? That assembly was mounted to a fixed tab with two phillips screws. I couldn't get enough purchase on any screwdriver to loosen the screws, but that was partly because I was handicapped by not being sure that that was what I wanted to do. If I know that I can safely remove the whole pilot assembly, I'll figure out some way to get the screws loose. But maybe there's no benefit? I should be able to replace the thermocouple just as it is---I took the existing one off and put it back on once already. I wouldn't take the pilot assembly off unless there was reason to believe that it was part of the problem. What do you recommend?

Stan

Stan, were you able to get the pilot light going with the button pushed down? After awhile did the pilot go out when you turned the knob to let it run?

How big is the flame, it doesn't take much. If its not running when the knob is turned there is one issue, if it stays lit thats good.

If you can get the light to keep burning until the furnace tries to light, that is where you would take out the whole assembly and clean it.

No, the pilot flame would go out even before my finger was completely off the button. I take it that it works by the button opening a valve to let gas flow to the pilot. Once the pilot is lit, the flame heats the thermocouple which sends millivoltage to the unit which then holds the valve open so you can release the button. But that never happens. The flame only stays lit until you release the button. Bad thermocouple, I now understand. But why? The furnace has only been in operation since late October, and not that much---we've had a warm winter.

Stan

> But why? The furnace has only been in operation since late October, and not that much---we've had a warm winter.

Remember, the pilot is on all the time, and was probably on all through the summer. The usual cause of premature thermocouple failure is an improperly adjusted pilot flame. Check the installation instructions for the furnace and see if you missed any adjustment steps. Usually the pressure needs to be checked with a manometer, and the flame needs to be adjusted so it's just big enough to set the thermocouple.

(quoted from post at 00:41:55 03/12/13) No, the pilot flame would go out even before my finger was completely off the button. The flame only stays lit until you release the button. Bad thermocouple, I now understand. But why? The furnace has only been in operation since late October, and not that much---we've had a warm winter.

Stan

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The thermocouple works by having the junction of two dissimilar metals heated. When heated they generate that milli voltage. The safety coil in the redundant gas valve will be held in only when the milli voltage generated by the thermocouple matches it. You are bypassing that safety coil by depressing the button long enough for the milli volts to take your place. Typically what you are describing is one of three things: 1) Bad thermocouple 2) Insufficient heat on the thermocouple end...too small of flame or flame is so high it is actually bypassing where it needs to be 3) Defective holding coil in the safety circuit.

Why possibly a bad thermocouple? We are finding poor quality of products flooding the US market in virtually everything, why not thermocouples too... Usually if the junction of the two dissimilar metals (swelled up end) of the thermocouple is intact it will generate sufficient milli voltage, but that is no longer true with the lower quality of materials.

Though a slim possibility, the same applies to the redundant gas valves holding coil. If bad, the gas valve needs to be replaced. The easiest way to check it is with another new thermocouple. This will ring true ONLY if the pilot is adjusted properly and coming in contact with the thermocouple properly.

Make sure you have a strong pilot flame encompassing a minimun of 1/2 to 3/4" of the end of the thermocouple. There should be a nice inner core of blue with a different softer and larger outer ring of blue with NO yellow. Yellow or white in the flame will indicate imminent carbon build up. A tad of orange is all right as usually that will be superficial rust particulate sucking into the flame as you are or have been disturbing the area surrounding the pilot with all your work. That will go away mostly. Please keep us informed on what you do and what you find.

I've checked thermocouples with a DC volt meter and a propane torch.

Dusty

Yeah, I too have a few tricks up my sleeve and have done the same thing...I used to carry an old "Baso" switch to check the thermocouples with. Just left the pilot assembly in the furnace, unscrew the end into the gas valve and screw into the Baso and relight the pilot while holding down the redundant valve to maintain pilot gas flow. After 10 maybe 15 seconds, depress the Baso switch and if it holds in then the thermocouple was generating adequately. I have been doing commercial and industrial for the last 25 years so this old school technology (if you can call it that) is slowly going by the wayside. I probably haven't touched a standing pilot in a decade.

I was thinking he probably doesn't have a dvom and was going for the basic description of the pilot circuit sequence so the repair can be made with nothing special.

He's gotten a lot of good suggestions so far and I am confident he will figure it out.

I see everyone giving advice, I don't see the proper advice given, so here goes, Get yourself a qualified furnace repairman for your rental properties. By messing around with a furnace in a rental property you are taking on more liability then you can ever know. friend of mine just took the front off the furnace in a rental house he owned. A week or so later it blew up, He will be paying for the rest of his life, he cant get out of the liablility by declaring bankruptcy.

Tom, you are right, do not mess with it.

(quoted from post at 20:54:06 03/11/13) Hi missouri massey man,

You mentioned that I'd need several wrenches and a long phillips. I should be able to replace the thermocouple just as it is---I took the existing one off and put it back on once already. I wouldn't take the pilot assembly off unless there was reason to believe that it was part of the problem. What do you recommend?

Stan

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Typically the thermocouple is held into the pilot assembly with either a plated or brass 7/16 ferrule type fitting. The other end screwed into the gas controller requires the 3/8" end wrench. Some cheaper units have nothing more than a retaining clip holding the thermocouple into the assembly. You should know by now what you needed to remove it, so you will need nothing more to re assemble it. However...while the pilot light WAS burning as you held down the knob (or valve handle) did you get to see just where it was burning on the old thermocouple and was is a good dual blue flame with no yellow/white ? If so you can just leave the pilot assembly in and just replace the thermocouple in the reverse fashion of how you removed it. If however, there was any yellow to the flame, there is going to be a tiny bit of debris in the pilot orifice and you will have to remove the assembly to clean it.

The pilot orifices on propane are tiny, natural gas pilot orifices are slightly larger. DO NOT ream out the orifices, you will create another problem... use compressed air if necessary. Chances are, you merely had a defective thermocouple. However, if there was a lazy yellow flame before cleaning the orifice AND it is still there after cleaning it, you more than likely have a gas pressure problem and without a picture of the controller I can't tell you how to adjust it on your own without specific tools probably not at your disposal.

I certainly hope this is not too confusing but I'm trying to be as specific as possible flying blind...Sorry for the late reply, I was out to dinner with the family.

Post back if it is Nat gas or Propane. I must have missed it in your earlier post, will go back and re read.