Atwood Hydroflame 8531-II furnace issues

Some furnaces not all have a switch in the furnace housing to shut it off from outside.

Wa8yxm: Not sure what you meant by "Turn the switch on top of the motor housing off"

There is no switch that i can see on this furnace.

thanks....John

Outside remove the cover, Turn the switch on top of the motor housing off, Go inside and crank up the stat (if you can) so it runs (or simply bypass it) now turn the switch on and observe,, You should hear

Fan start, then you will hear a CLICK as the gas valve opens (you may touch the coil, it is only 12 volt, and you will also feel it open) you should then hear the SNAP SHAP SNAP of the Direct spark ignition, and it should FLAME ON, you will see and or hear the change in sound when it burns.. Then likely 3 seconds later it will shut down the flame, then it will light again, and again, then teh blower will shut down and a LED on the control board on the left will go BLINK BLINK BLINK (3 times it blinks)


IF that is what is happening ... then here is the suspect list.. If that is not happening post and we will go to next level.

Flame heats a probe (Thermocouple) which generates a small voltage (just under 1/2 volt or if you like accuracy 480mV) (o.480 volt)

This is sensed (or rather it is supposed to be sensed) by the control board.

This is not happening

Possible causes are poor burn, dirty thermocouple not heating fast enough, and in my case BAD CONTROL BOARD.

If you decide on Bad Board.. I ordered a Dinosaur Board from American RV in California.. Less than half the cost, More than twice the quality (Humble opinion) put it in in 2011, last time I tried furnace.. Worked.

(NO I will nto try furnace today it is still over 80 out)

Sail switches normally do not fail. A small amount of debris can prevent them from operating.
A failing motor causing the motor to slow down slightly could cause the sail switch to open causing furnace to shut down.
Yes, it can be bypassed. It is located on the blower housing toward the back with a small arm sticking into the blower housing.
Do not leave the furnace un-attended while testing with safety type devices bypassed.

Thanks OLD-BISCUIT...i'll check those. I have a new regulator on as when i initially opened up the tank there was propane coming out that little pinhole. So i changed the regulator.

ENBLETHEN...I already checked the thermostate by bypassing it..no luck.

DARSBEN.. Thanks for the manual.

KEN WHITE...i cleaned the sensor and verified the gap but possibly it still could be faulty???

As far as the sail switch goes, can it be bypassed to see if it is faulty by unhooking the wires and jumpering them?

I'll have to pull the board and have it bench tested.

Thanks for the help guys. I'll keep plugging at it. Raining here today so i won't be at it.

Regards...John

Same thing happened to our unit. All checked out too! I took a chance and changed the sail switch for 20 bucks. All good after the guess...

Sounds like an issue with the flame sensor or it associated circuitry.

Click here for the repair manual with troubleshooting guide for your furnace

Could be the thermostat.
Try connecting the two thermostat wires together at the 'stat. The furnace should start and produce heat until the wires are separated, then go into cool down mode and shut off shortly.

The only other things to check:

Gas pressure at furnace with at least 50% of other gas appliances ON....needs to be 11" WC (minimum pressure for furnace operation)

Bad flame sensing ire between electrode and circuit board.......it can supply the high voltage needed for ignition but if it is grounding or not making good contact the milli-volt flame proving signal can't get to circuit board.
Part number 33661....but may not be available any longer?

Circuit board.......pull and have it bench tested

Exhaust blocked
Gasket leaks
Heat exchanger warped/cracked