Pilot on, fan on, burners won’t fire up
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Saturday I noticed no heat in office. Fan was blowing cool air. Sunday I turned heat up, same thing. Jiggled a few wires on the furnace and burners came on. This morning had the same problem, no burners lighting even after jiggling wires. Any ideas of what I can check before calling HVAC guy? Wires seem to be all connected ok.
Replies
If jiggling the wires did it, it's probably a bad connection of the thermostat wiring. The stuff is generally pretty haywired, and loose connections or broken wires aren't uncommon.
If not that, it's thermostat, transformer, or gas valve.
just checked the wires I could see easily, all good. I'm thinking it might be the gas valve as you say. I'm going to the manufacturer web site for more info. Thanks
just replaced the batteries in thermostat and switched off than back on the switch on gas valve and it fired up. not sure which did it but it's getting toasty, for now at least. thanks again
Does it have a standing pilot or a Honeywell "Smart Valve" with intermittent pilot? Does it have a draft inducer fan? If it does, the usual firing sequence is:inducer fan on to establish draft
hot surface igniter on
pilot on
burners onIf the pilot comes on but no burner it's either a faulty pilot heat sensor rod or a bad Smart Valve. Sometimes turning the power off to the whole system for about 5 minutes will resolve the problem temporarily. An igniter/sensor assembly will wholesale for about $30 - a new Smart Valve will cost another $100 or so. I usually replace both and eliminate the possibility of a call back.
There are several "safeties" in the start up circuit that will prevent fire in hole when things aren't all right.
Usually, an operating fan in the presence of a call for heat (i.e. thermostat is working) and a lit pilot (i.e. gas is not shut off), with no gas valve opening is due to a roll-out or high temp limit switch tripping or "opening". Most hi limit switches will reset automatically, roll-outs will not. This is my best guess. The roll-out switch and/or wiring to/from this switch is faulty. A $10 item at the loacl Berkheimer store.
Thanks for the reply Tim. There was a sliding switch on the Gizmo with the gas line attached which was marked on and off. I moved it to off, than back on and it fired up. This was Tuesday and there's been no problem since. Thanks Again
The gizmo with the switch is the gas valve, and by your description, I'd guess a Honeywell SmartValve. Based on changing the position of the switch to off and back to "on" and the results that you are seeing leads me to believe that 1) you still have a propoblem that has temporarily cleared, 2) that my initial guess at the cause was not accurate and 3) that the cause of the problem is one of the pressure switches.
Does your furnace have a draft inducer (usually called a "power vent")? Is this the "fan" that was on when the burners wouldn't fire?
If this is the case, I had exactly the same problem on my furnace a few months ago. I replaced the pressure switches for about $30 and have had no problems since.