no current to furnace

[achenier7]

My 30+ year old Lennox exterior furnace made a strange booming noise when i started it after many months with the gas line valve shut off.

I immediately shut off current at the breaker, and now it won't start at all. Can't even get the fan to work on manual.

Is there an automatic safety shut-off somwhere in the system that would have been tripped by the condition that caused the noise?

AC

[HayZee518]

I don't see why a "noise" would shut anything down. My thoughts are if there is a combustion blower, then it wasn't working and the accumilated gas/air could've ignited when the ignition turned on. The standing pilot if there is one and its flame detector couldn't be operating allowing gas to go into the combustion chamber and ignited with a whooomp! if the breaker won't reset check the path for the electrical. something's shorted out - control transformer primary, blower motor, etc.

[achenier7]

This is out of my league... I was planning to replace the furnace anyway.

I am debating whether I should install a replacement exterior furnace, or a high-efficient model in the house crawl space (no place in the house for a furnace). With energy rebate, the cost would be about $2 000 more for the high efficiency model. We do not expect to stay in that house for more than 5 years, so we are not sure if the high efficiency unit is worth it. Any thoughts?

[jnaas2]

The sound you heard may have been the furnance ignighting and flame roll out, it sounds like a professional needs to look at it if you plan on keeping it. Some models do have a flame roll out switch that will kill the power to the unit or it may have shook something loose. Have the furnance man or woman figure how long it will take to pay for the high effecient unit compared to the other one, also it may help in five years when you sell the house if you go ahead nd install the 90% plus unit now