Anyone here experienced with HVAC? I have an old (early 70's vintage) Coleman Presidential central heat & air unit and I just lit the (natural gas) pilot light the other day. Last night and again this afternoon, the pilot light has gone out. Never in the 13 years that I've had this unit has this happened before. It always lights easily and no other pilot lights (stove, oven, hot water heater) are out so I know that it's not gas supply related in general. There is a very strong draft up the chimney as I can't light a match and then put it in thru the inspection hole - it'll blow it out every time. I have to use a long BBQ/Candle butane lighter and light it inside the furnace to light the pilot light.

Ideas? The thought of lighting the furnace twice a day doesn't really appeal to me.

 

Guess I should add that the pilot burns blue and the thermocouple seems to trigger fine except when the pilot is out.

 

Someone else will have to answer to the lighting problem, but I would suggest that you look into a new HVAC system in general. The new high efficiency systems are known to pay for themselves very quickly when replacing a 30+ year old system...

Just my $0.02

 

True and good advice in general but probably not in the case of a 30+ year old mobile home that I hope to be out of in the next 12 months. Thanks for the suggestion though.

 

I'd replace the thermocoupler anyways. They are cheap and it will eliminate that as a source of the problem. If the thermo isn't signalling the snap action valve it will snap shut and close the gas circuit for the pilot. I'm certainly not an expert on coleman furnaces... I avoid them like the plague. We have a few around here and they are a pain to light through that little porthole while holding the cover open and pushing the button. Grrrrrrrrrrrrr I hate those things. :0)

 

If the pilot will not stay lit then you will need to replace the thermocouple. The whole pilot assembly may have to be taken out to be cleaned, there is a very small hole in the orifice that gets clogged or rusted up, most likely from the pilot not being lit over time. This causes a weak pilot. The pilot can be adjusted but you may want to let a heating guy do this.

 

Well, is stayed lit from when I posted on the 25th thru yesterday or part of last night (the 27th). I had to relight it this morning again. Guess I'll have to look at replacing the thermocouple unless someone else has a different suggestion. Can anyone tell me if that it a generic unit or if I need a special part for this thing? What all is involved in replacing it? I have a 6" diameter inspection hole to work thru so it would help to know what I was doing before I stick my hand in there.

 

the pilot lite flame is to small, the flame is being blown out when the furnace is trying to relight. the orifice on the pilot may have some rust partially blocking the hole. just clean the pilot. disconnect then reconnect the thermo couple, to ensure you have a good connection. (this will help if you have just a speck of corrosion on the thermocouple connector).
if this doesn't help you may need to replace the pilot lite orifice.

 

Hmm, that does make sense because one time I could have sworn that I heard the furnace start to light and then go out. Guess I'll try to clean it this evening when I get home and see if that helps at all. If not, then try a new thermocouple.

Thanks for the suggestions and advice.

 

From the way you describe things, your mess may be like this (as far as components go):



The thermo-couple would slide in the compression looking thing on the right.


If the flame appears too small, then the pilot orifice is most likely partially blocked with corrosion. The pilot orifice is in the picture above (middle bottom). It's shaped a lot like a sewing thimble and made of aluminum. The corrosion will most likely present as some white crusty stuff.

The problem is the actual hole (orifice) is very small. To clear the blockage will require the real tiny wire drills. I'm not sure of the drill number, but it's in the Hair range or smaller size.

The fact of the matter is that the thimble's most likely stuck in it's housing due to the corrosion and will be very difficult, if not impossible to remove without damaging it. To add insult to injury (sorry), the flame director (the little hood thing) is in the way of making a direct shot at the orifice while it's installed in it's housing. My point here is that, if you can't remove the thing, then you're stuck with trying to clean it while in place. The frigging hole is so small thet you really need to have some light shining through it to find the thing. The shroud's in the way.

You might try using a piece of fine wire to gently scratch around the orifice area in the hopes of clearing the blockage.


Good luck, and I hope this helps.