Gas and Oil Home Heating Furnaces - gas furnace ignition delay...boom

I've got a rather old (20yr) attic mounted forced air gas furnace, and recently it has been having some problems igniting the burners when the thermostat requests heat.

Basically, it sounds like the valve is opening, and gas is being delivered, but for some reason, it's not igniting in the presence of the pilot light, and so after a few seconds, it finally lights with a rather loud boom.

The problem is intermittent, and happens most often when "cold" starting. After the furnace has been working for a few minutes, it has no problem relighting later on.

Any tips would be appreciated. Thanks,
-Daniel

This can be a very dangerous situation. Sounds like the burners and train need cleaned. Also could be that the pilot is not in a good position. If you're iffy about doing this call a pro asap to fix this problem. Boom is definetly not good.

Sounds like it needs a cleaning.........the gas carryover device may be blocked/interupted too...the simple is usually the cause....dirty logs...PM!!!!!

:)

Im with the rest here When was the last time you had the burners cleaned out good. Sure you dont have any spiders down in the venturi tubes there. If LP or NAT is the gas regulator for the unit ok?;) ED

burners dirty or rusted out. THI IS DANGEROUS, call a pro. 20 yrs old? in the attic, going BOOM?! and still running it? you are a brave man, have it serviced thoroughly, replacing it will pay for itself in energy savings in short order. if it is dirty burners, in a 20 yr old furnace, the dirt is generally rust from the heat exchanger, another reason to consider replacement

hey guys,

thanks for the advice. professional is coming tomorrow to check it out. can i clean out the burners (and upstream gas supply) myself, if that's what the problem turns out to be?

-daniel

You could clean it out yourself, but if the system has never been looked at over the 20 years of it's life, It's for sure due for a cleaning, and heat exchanger check up.

It would be bst to leave it for the pro to do.. $$$$ can't replace your life, and loved one at home.

thanks everyone for the help. a pro from the gas company came to check it out, and helped me fix the problem.

it was a really simple thing. he said the flame just wasn't traveling down a rail which spreads the fire from the pilot to all the other burners. some light taps on the rail with a wrench while the gas was on was all it took to clean it out.

everything else seems to be in good shape. furnace works great now.

-daniel

the gas carry over tube...but if he didn't brush the tube it's whole length, I think you'll hear from it again...at least you'll know where to go though.. The Carriers use two flat pieces of sheet metal on each log,...some guys call it a pilot zip tube