Atwood Furnace Problem. Help?

dougrainer wrote:
1. Turn the furnace on, then go outside to the outside vent. Wait until you hear the Ignitor click. When it does, IF the gas valve is opening, but does NOT ignite, you will smell the LP. If you do NOT smell the LP, then the gas valve is not opening. A quick test for the gas valve is this, you access the LP line where it is connected to the Gas valve on the furnace, you attempt the Light sequence, when the Ignitor clicks, you whack the gas valve lightly with a hammer. IF the furnace lights, you have a defective gas valve. If it does not light, then you may still have a defective gas valve, but you need to do more testing. Gas valves can fail when the temp gets to freezing and the valve body contracts from the cold slightly to keep the plunger from pulling down. Your year model as you found out does NOT shut down after a no light, but continues blowing cold air. Doug

I did whack the gas valve and the furnace has started and restarted for the 6 or so times I have tried it in the past two days. Thanx to everyone for their help!

1. Turn the furnace on, then go outside to the outside vent. Wait until you hear the Ignitor click. When it does, IF the gas valve is opening, but does NOT ignite, you will smell the LP. If you do NOT smell the LP, then the gas valve is not opening. A quick test for the gas valve is this, you access the LP line where it is connected to the Gas valve on the furnace, you attempt the Light sequence, when the Ignitor clicks, you whack the gas valve lightly with a hammer. IF the furnace lights, you have a defective gas valve. If it does not light, then you may still have a defective gas valve, but you need to do more testing. Gas valves can fail when the temp gets to freezing and the valve body contracts from the cold slightly to keep the plunger from pulling down. Your year model as you found out does NOT shut down after a no light, but continues blowing cold air. Doug

Thanks for asking this question. We're not having any issues at this time, but I'll print out the info and keep it in our book for future.

This is such a helpful forum.

I think an insect web can be ruled out as the reason as well since the furnace apparently stopped working during the night. I'd think the issue is around the thermocouple or the board.

My furnace cut out in a cold (below freezing) night, and the reason was that there was only Butane in the bottle which doesn't evaporate at that temperature. I don't think this could apply to the OP, though.

Yes, we do have gas. The stove works fine as well as the water heater!

Thanx for all the info and suggestions. I will try and get to it today and report back.

How the furnace works (Well steps in operation)

1: Thermostat calls for heat
2: Control board starts blower (This is happening)
3: Sail switch closes (It appears this is happening too, the sail switch is closed by the movement of air across a plastic paddle or "Sail" it is inside the furnace).
4: Control board opens gas valve and begins ignitiion sequience (Starts making sparks) you said you heard the sparks.. Did gas flow.. See note 1 below
5: Burner ignights (you said this did not happen)
6: Thermocouple heats up
7: Control board either senses .480 volt (480 mV) from thermocouple.. .or not
8a: If it does operation continues till T-Stat says "Hot enough"
8b: if it does not it tries agin, usually 3 times, then locks out.
9 Burner shuts off
10 Blower shuts off.

Note 1: for gas to flow you need gas to flow, the valve must be open, if your propane (Explosive gas) Detector operates an emergency cut off solenoid it must be on and functioning properly.. The solenoid on the furnace must be functioning properly and finally.. There is an insect that likes to nest in the burner orifice completly blocking it so gas can not flow (or other debris).


On my furnace the burner did light, i could hear it light, and the thermocouple made with the .480 (I tested it) but the control board.. Failed to detect it

This can be due to a bad connection but that was not my problem (I made sure of it)

It can also be due to a bad control board

OEM board, roughly 250 at the time
Dinosaur boards "Generic" repalcement, 108 INCLUDING S&H, And it's a better board. Very well built in the USA board. Better design too.

I do not, however, think the control board is your problem.

I had similar situation. Shop replaced igniter electrode and problem was solved.

fishing2 wrote:
I agree with Old-Biscuit and add sail switch and temperature-limit switch

OP is getting spark.....no flame
Sail switch/high limit switch bad..power would not get to circuit board for ignition

I agree with Old-Biscuit and add sail switch and temperature-limit switch

I agree with checking to make sure you have propane. I have had the same thing happen when I ran out of propane. The furnace just kept on running but no heat.