Re: [EE]: Flame rectification

Thanks Bob,

I don't have a pilot. I have a hot surface igniter (big glow plug). The 
firebox ground seems to be good as I used the firebox as the ground 
reference when measuring the various voltages. All were exactly as 
expected. Today I cleaned all the orifices. They produce a nice blue 
flame. We replaced the controller board a week ago when it was falsely 
reporting that the limit switch was open when it was not, and other 
erratic behavior. The new board seems to have fixed all that. Now we 
have a consistent error where the flame comes on for about two seconds 
then shuts down with an error message saying the system shutdown because 
no flame was detected. We replaced the flame detector although the old 
one seems to be in good shape. The flame sensor has the correct 90V to 
ground. I couldn't measure the current because it should be in the range 
of 2-3 micro-amps and none of my meters will go that low. Today I 
purchased a meter with that capability and I hope to try it Friday or 
Saturday. This thing is driving me nuts. My daughter is heating her 
house with a wood stove and an electric heater. She cannot add more 
electric heaters because she only has a couple of outlets with modern 
wiring. Most of the house uses ancient knob and tube wiring which can 
only handle a few amps per circuit.

One other thing we did was fill it with water. It shocked me to discover 
that a high efficiency hot air furnace needs to have water in it but 
apparently it does.

Thanks for your help,
Allen Mulvey

On 12/24/2025 3:33 PM, Bob Blick wrote:
> Hi Allen,
>
> Several things are important for it to work. The gas valve has a few wires. One is ground.
> There must be a ground wire from the gas valve to the control box. The control box uses that as part of the sensing circuitry.
> The tubing from the gas valve to the pilot must have electrical continuity.
> The pilot flame must surround the flame sense electrode and not wash too much on anything that is grounded.
> If there is too much draft, it can push the pilot flame around, that's bad. Maybe the garage door has a gap and there's random airflow around the furnace.
> Also the flame must be blue, if there's yellow the gas atoms have lost their charge. Hopefully you have a viewport to observe the pilot in action.
> You can clean the pilot orifice with a cat or dog whisker without risk of damaging it.
> I've heard that Johnson integrated gas valve and ignition systems go bad, but that's just hearsay. I have a Honeywell system with separate valve and ignition module and it's been working since 1997.
>
> Hope this helps!
> Friendly regards, Bob
>
> ________________________________________
> From: Piclist<[email protected]> on behalf of Allen
> Sent: Wednesday, December 24, 2025 4:44 AM
>
>
> I have been working on (baffled by) my daughter's Payne high efficiency
> furnace. The flame detector seems to be a simple steel rod. It has only
> one electrical connector with about 90V on it. I assumed, at first, that
> it was some kind of thermocouple referenced to ground through its one
> mounting screw. However, the path from the connector to ground seems to
> be open. Diagnostic instructions indicate that it should carry .5
> micro-amps or more. It looks like the flame provides the path to ground.
> It it gets dirty it doesn't work. Does anybody know anything about this?
>
> Allen