Gas furnace back pressuring?


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Old 10-19-09, 03:38 AM
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Gas furnace back pressuring?

We turned on our gas central heating system and, it worked for a day then we heard what sounded like a small explosion, upon checking we saw the the pilot light was turned of and the force blew the cover of the unit off so we are scared to relight.

We have had this house for 12 years and have never serviced the unit, I am being told the problem is that maybe we have a clogged chimney so the system is back pressuring and tht is what blew out the pilot and cover? Any ideas what went wrong here and if there is anything I can check myself please?
 
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Old 10-19-09, 08:37 AM
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It's pointless to speculate. You are 'way past due for having the furnace serviced and inspected.

One of the problems with do it yourselfing is that people concentrate on repairing the specific problem that is bedeviling them, but they have neither the experience nor judgement to look at all the systems of the furnace to identify orther possible or incipient problems and correct them.

That's what routine maintenance is all about.

Any devent repairman fixes not just the particular problem, but assesses the condition of the whole furnace and either completes any needed maintenance or advises the owner what needs to be done.
 
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Old 10-19-09, 05:46 PM
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What kind and how old a furnace? And is it power vented or not?

If powervented, you should not have a pressure that can blow out the fire, due to backpressure in the chimney, because there is a safety pressure switch that should shut down, to prevent that.

But you could have real dirty burners or cross over, would be my guess. That could cause delayed ignition where the combustion chamber fills with gas......too much gas.....and finally ignites, with usually a noticeable WOOF sound.
 
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Old 11-01-09, 03:08 PM
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Originally Posted by ecman51`
What kind and how old a furnace? And is it power vented or not?

If powervented, you should not have a pressure that can blow out the fire, due to backpressure in the chimney, because there is a safety pressure switch that should shut down, to prevent that.

But you could have real dirty burners or cross over, would be my guess. That could cause delayed ignition where the combustion chamber fills with gas......too much gas.....and finally ignites, with usually a noticeable WOOF sound.
I think you've nailed it, I called a boiler guy who told me first to get the chimney cleaned which I did but he said he doesn't think that was the cause of the problem as the chimney was not clogged and he said that I will need a new Pilot assembly because one of the gas line's end on the assembly was burnt out so too much gas was entering the chamber but I can't find a Pilot assembly yet anywhere for this old Thatcher boiler so he said only thing I can do is to convert to another modern gas supply system which will involve myself having to get an electrician also to do some re-wiring.

I tried all local stores here in NY and online but I cannot find the assembly anywhere, any leads please?





My old Thatcher Gas boiler need a new Pilot assembly but I can't find one anywhere locally here in NY or online, help?
 
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Old 11-01-09, 05:22 PM
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Most repairman carry a variety of pilot burners that can be used to replace an existing pilot burner if it can't be re used, which happens from time to time. A repairman who leaves such a thing up to the customer doesn't sound like much of a repairman to me.

What you described in your first post was very likely a delayed ignition problem, not a venting problem. Delayed ignition is when the main burner gas turnsw on but doesn't light off the pilot burner promptly. The gas accumulates until it does like off, often with the kind of mini explosion your describe.

Usually a delayed ignition problem is caused by either dirty burners or a dirty pilot burner, or both. It's usually pretty easy to correct.

So ecman and I agree (and he likes to accuse me of never agreeing with him!)

I'd get back with your repairman and ask him to install a generic pilot burner to replace the one that is not good. Probably 90% of the time I could replace a furnace or boiler pilot with parts I carried with me, and most of the rest of the time I could shop for a generic replacement without much difficulty.
 
 

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