On 1/15/2013 12:20 AM, Zen wrote:
Just as it gets cold, my Payne hot air propane-fired furnace broke!
http://www4.picturepush.com/photo/a/...g/11964117.jpg

All of a sudden, the blower just blows cold air constantly without letup.
The pilot flame never starts.
Obviously, the gas never lights up either.

This happened, all of a sudden.

Normally, it has an electronic pilot, which lights the gas about a minute
after the blower starts. There is plenty of propane.

Any troubleshooting ideas?

I think there are three main components:
1. The flame apparatus
2. The circuit board
3. The lockout switch

I'm inclined to just buy all three, and replace (and have a spare), since
I remember the last service call was expensive and the circuit board was
replaced in seconds after a three week wait for the parts to arrive.

Do you have any idea WHERE I can get the three main components?
http://www3.picturepush.com/photo/a/...g/11964131.jpg

Probably a bad idea to just start replacing parts.

It's strange that the main blower starts up at all, because normally it
doesn't start until after the flame is detected by the flame sensor and
the burners start (so it doesn't blow cold air), unless you have the fan
always on at the thermostat.

The sequence should be:

1. Draft inducer fan starts up and closes switch (via suction) so the
controller knows that the draft inducer is operating and it's safe to
light the burner. You can check this with an ohm meter, or jumper across
it to test it (however it must be open when the furnace starts, then
closed after the draft inducer fan starts, you can't jumper it closed
before the draft inducer fan starts).

2. Glow plug heats up (or spark ignitor starts sparking). You can check
that a glow plug is getting power with a voltmeter (should be 24VAC) and
you can see it glow red. A spark ignitor should make a noise.

3. Gas valve opens and burners ignite. Audible thunk as the solenoid is
activated. Controller knows that the burners are lit by looking at the
flame sensor and will close the gas valve after a short time if there is
no flame. You can test the gas valve by turning off the gas to the
furnace, unplugging the wires to the valve, and connecting 24VAC or so
to the valve from a small transformer. If you hear a thunk then the
solenoid is activating and the gas valve is probably okay.

4. Main blower starts up.


If one of the flame-out sensors is bad (open) the gas valve won't turn
on. There are usually three or four flame-out sensors in series. If
there's a crack in the heat exchanger then flames can shoot out the
front of the furnace and the flame-out sensors will shut off the gas.


When my furnace broke a couple of months ago it was an intermittent gas
valve.

When my friend's furnace broke last month it was an intermittent draft
inducer fan switch (sometimes it's just a clogged suction hose, but this
time the switch was bad).

If it's an older furnace with relays on the controller board you can
hear the relays click as various things are activated. The draft inducer
fan relay will click, the ignitor relay will click, and the gas valve
relay will click.