SF-42 furnace won't start

BobW · 12-26-2009, 12:35 AM

We have a 2006 Elite with a SF-42 furnace. Went out tonight to heat it up. The fans come on and it looks like I can hear some clicking. No heat. I tried turning the unit on and off a number of times. At some point a short blast of hot air comes out of the outside vent. Then nothing. The fan stays on. Plugged into 120 and I have 13 volts.

Motor31 · 12-26-2009, 08:01 AM

First thing to check, do you have a full tank of propane with the valve wide open? It sounds like it is sensing no or low pressure.

GlennWest · 12-26-2009, 08:47 AM

Mine wouldn't come on the other day. Wife was cooking at stove with gas. Pressure was low"running on fumes". Changed out bottle all was well. jfyi

BobW · 12-26-2009, 11:50 AM

Both tanks are full. Just before the igniter clicks on, I can smell gas coming out the outside vent. So I'm sure it's getting gas. Fans work.

RGordon · 12-26-2009, 05:26 PM

I would look into the openings on the outside for wasp nest or mud dobbers. This will cause restriction of air flow preventing furnace from firing.

BobW · 12-30-2009, 10:55 AM

I found out the problem. After taking the heater out of the case, I took the burner out and found the gap in the electrode was more than 1/4 inch. I adjusted it to 1/2 inch and everything works now.

RGordon · 12-30-2009, 11:33 AM

According to the service manual the spark gap should be 1/8" and is also used to complete the circuit through the ionized gas to the control board. You may still have issues!

BobW · 12-30-2009, 12:53 PM

That was to be 1/8 inch.

Diesel-Gypsy · 12-31-2009, 09:32 PM

Great!
Now I need to remember that tip....

Any idea how that gap got widened-out to 1/4" ?

Rick

BobW · 01-01-2010, 04:16 PM

Quote:

Originally Posted by Diesel-Gypsy

Great!
Now I need to remember that tip....

Any idea how that gap got widened-out to 1/4" ?

Rick

Just like any spark plug, the electrode evaporates from the heat of the spark. I think this is something you need to do every couple of years. By the way, it takes only one screw to undo the heater, disconnect the wires (4) and the gas line. The heater unit just slides out of it's metal box. You do need to take off the outside panel.