Intermittent furnace problem - won't turn on sometimes (pilot IS lit)?

Question

We have a gas furnace that usually works just fine. There is an intermittent problem that surfaces occasionally, and it seems to come up on the coldest days. Maybe the amount of use it gets on colder days worsens the problem... I'm not sure.

When the thermostat triggers the heater, I can hear it click on, and I hear the heater start to rev up. It gets to the part where I usually hear the big "WHUP" of the gas inside igniting, but it doesn't happen. Instead, the whole system just kind of... winds down and turns off. Very disappointing.

It sometimes helps if I take the front panel off and gently shake all the wires and connections a bit. I'll put the panel back on and try it and everything will ignite and heat wonderfully. But when it's happening a lot, this only fixes it the first few times. After a few times, even this won't work. At that point, a whack to the side with my fist will usually get it working. If not, we just wait an hour or so until it comes on.

Answer 1

you need a new ignition assembly couple hundrend bucks installed not to bad


My husband is a furnace/air/refri man

Answer 2

There is a little safety switch inside the front panel so it won't "flame" while the front cover is off,sometimes the panel vibrates just loose enough to release the safety switch ,Do you have central air connected?sometimes the outside air intake/exhaust clogs up and it doesn't get enough flow for cold day's and running a lot,well that's the cheap fixes and common do it your self problems and also is your filter clean?

Answer 3

By your discription it sounds like a loose wire. Try disconnecting the power to the furnace then taking each wire loose from the slid on spade clip and with pliers slightly crimp the female end a slight amount and then put the clip back on. You will have to go through each and every wire as the problem could be anyone.

Answer 4

The heat exchanger is going. There is a crack in the unit and it's loading up with gas. The volume of gas isn't being ignited, so it builds up. When the ignitor finally does it's job, you get an explosion of the unvented fuel causing the 'WHUP'.
It would be less expensive, not to mention allot safer, to replace the furnace. Failure to do so will cause lose of life and property.

Answer 5

More than likely the pilot orfice and the pilot sensor need to be cleaned. But this will have to be repaired by a qualified hvac tech.

Answer 6

Cameron is right. I'd suggest that you get it done soon because it could cause a serious boom boom problem.