8531 /Burner Issue UPDATE--Photos ( Fixed!)

[BFL13]

With the furnace running, where do you put the pos and neg leads of the meter? Or can you do it at the Tstat inside with the furnace on?

I want the 12v to the board, not the voltages the board puts out to the various components. eg,I got 10.67 at the gizmo on the right of the fan casing and some metal nearby, but I don't know if that is the loaded 12v with the furnace running or what.

Thanks

[MT_BOB]

Yes it is a gasket,it is sold separately-- 32172
You have 1 probe,1 igniter, and 1 ground for the igniter. All 3 should be closer to the burner. What you do to bend them is use 2 pair of pliers,go further up the "shafts", hold with 1 pliers and bend with other. Keep the distance the same between the igniter and it's ground. Do not bend by just pushing on them,you can break the ceramic insulator they are mounted in.
As far as other issues,you also may have the snap switch going bad, they can do strange things,
and,I believe your voltage differential is not good.

(it matters not where you bend them)

[BFL13]

Could be the control board--I did just clean the edge contacts so have to try that first when I put this thing back together.

Found the other metal part in my spares box--it has the white gasket in better shape than the one in use. Now I don't know if the gasket should be better or keep using the one there now. What is it for?

Ok, do the screws make a ground contact between the two pieces of metal so the idea is to clean where the underside of the screw tops touch the plate? (And the underside of the screw tops as needed.)

[enblethen]

Do not remove the gasket. Clean area wher screw makes contact to the plate. Gasket is probably like an asbestos material.

[Gdetrailer]

Nothing special about the probes, generally there is nothing to go wrong with them.

Detection issues tends to be more with lack of good flame, lack of good connection from control board to ground or bad control board.

Flame must be correct with the probe inside the blue portion of the flame. Incomplete combustion results in poor burning flame which results in less or no blue portion and less or no conduction on the probe.

Best to use diagnostic info in the link I posted which measures the current flowing through the detector rod.

If flame detect current checks out then issue most likely is the control board failing.

[BFL13]

enblethen wrote:
I would clean the mounting plate of the rust. Make sure it has good ground contact.

Is the "mounting plate" the part that has the three prongs and has the white stuff between it and the other metal part? Do I scrape off the white backing stuff and try for metal to metal?

I could shim that so the prongs are tilted down more to the screen if that would help

EDIT-- looks like a papery sort of gasket--maybe it is supposed to be there and I better not scrape it off?



Here it is --no gasket? I will try for the other part to see if it has it.

https://www.amazon.com/Atwood-36998-Hydro-Furnace-Electrode/dp/B00CLSWK2U/ref=sr_1_10?dchild=1&keywo...

[enblethen]

I would clean the mounting plate of the rust. Make sure it has good ground contact.

[BFL13]

Got some photos I hope you techs can interpret.



Side view of three-prong above burner screen- can't bend them down closer





Top view--screen not rusted out, fairly new burner head.



The spade where the black wire goes on is rusty except it is shiny where it was covered by the black wire's terminal--I can't tell if the rusty outside part on the shiny probe part sticking out is clean inside making good contact or not. I will clean the end but can't do anything about where it is on the probe. The black wire seems ok but don't know where it goes to back towards the circuit board--clean that end too if I can find it?

EDIT--black wire to plug on edge of board--cleaned board contacts and plug--didn't seem to need it.

The rusty plate screwed on that holds the three probes has some kind of white stuff on it you see there so it is not making contact with the other metal part there (if it is supposed to) except maybe with the two screws. Is that the ground I am worried about?

[BFL13]

Thanks. I have the older three-prong type with the sensor separate from the sparker, but same idea. I will get at it later.

Don't like when it cuts out--suspense until it cuts in again. Would hate to have to come home from camping early if the furnace quits entirely.

[Gdetrailer]

BFL13 wrote:
I had this problem before (two years ago) and got some help on here with it all, and swapped some parts from a 111 I got off a guy. Eventually I got a 111's board from a 98 MH being parted out and that got it working right. New burner head (old one had screen rusted out) Now it is starting to act up again.

ISTR I swapped the squirrel cage fan-- found out how to get it off here--that was to try a new limit switch you have to get the fan off first to get at.

The one in there now is metal and heavier than the plastic one I have in the spares box. Can't remember which is the 11 vs the 111's. Anyway it spins ok, and the delay for burner on at the start after fan runs and then at the end for fan to stay on after burner off is working right.

It is just the burner cutting in and out when it should just stay on.

I can haul the burner end out again and check the wiring for the flame sensor and however it is grounded. Is there a way to check the voltage with it out? Maybe turn the Tstat to on? Is there any voltage when there is no gas?

Wiring diagram can be found HERE on page 9.

Burner cutting in and out..

Partial blockage of the burner orifice causing flame to not be correct size and position.

Flame detect not positioned correctly in the flame.

Flame detect grounding issue.

Fan running too slow or too fast altering flame position.

Bad control board?

Overheating?

Sticking or bad gas valve?

Flame detector is a dual purpose device, it is used to spark ignite the gas in the burner and once the gas has ignited, the probe now operates as the flame detection system.

As flame detector, the control board will place a small voltage on the probe. When proper ignition has occurred the probe should be inside the blue part of the flame. The blue part will conduct a small amount of electricity generating a small current that flows from probe to burner. Control board monitors the current drawn on the probe if no current or wrong current is drawn the control board will close the gas valve.

This is known as flame ionization detection, some times called flame rectification since the current flow is one direction only..

HERE is a good write-up on this type of flame detection with some troubleshooting info.

Ground is typically established through the burner assembly and burner assembly should have a ground connection to the 12V negative and control board. If in doubt that the flame sensor or burner may not have a good ground established, you can add a grounding wire to the burner to a known good ground to see if that helps.

[BFL13]

I had this problem before (two years ago) and got some help on here with it all, and swapped some parts from a 111 I got off a guy. Eventually I got a 111's board from a 98 MH being parted out and that got it working right. New burner head (old one had screen rusted out) Now it is starting to act up again.

ISTR I swapped the squirrel cage fan-- found out how to get it off here--that was to try a new limit switch you have to get the fan off first to get at.

The one in there now is metal and heavier than the plastic one I have in the spares box. Can't remember which is the 11 vs the 111's. Anyway it spins ok, and the delay for burner on at the start after fan runs and then at the end for fan to stay on after burner off is working right.

It is just the burner cutting in and out when it should just stay on.

I can haul the burner end out again and check the wiring for the flame sensor and however it is grounded. Is there a way to check the voltage with it out? Maybe turn the Tstat to on? Is there any voltage when there is no gas?

[enblethen]

Item to the right is a time delay relay.
That is too much voltage drop to the time delay relay. It could have burnt contacts. There is two connections. One input power, should be the 11+ volts, output to motor should be the same.
Does the motor spin freely?

[BFL13]

8531-11/111 mix (parts swapped here and there) has actual flame sensor, not the new two prong method like a 1V has.

Battery voltage start- 12.59
Battery voltage furnace running- 12.50
Voltage at furnace CB- 11.34
Voltage at thing to the right-10.93

Burner cuts in and out fairly often. Burner screen, sparker, orifice all clean. Manual suggests flame sensor voltage bad ground or too low?

Sparker and flame sensor is above the burner screen quite high, can't bend the three prongs down closer, but the two prong type as seen on a youtube is supposed to be closer to the screen than mine is.

Don't have voltage for the flame sensor after that 10.93, but could be lower than that?

[Gdetrailer]

Measure voltage at the leads that are supplying the furnace with 12V.

You should see a pair of heavier ga (14 ga, 12Ga?) wires which are not from the T stat that go into the furnace, typically they will be wire nutted on the outside of the furnace. You want to use both the pos and ground wires supplying the furnace. Grounding meter to metal anywhere else may skew the reading due to poor electrical connection from corrosion.

T stat wires going to furnace are typically lighter ga than the 12V supply from the fuse box (18ga, 20 ga, 22 ga?).

Can't take reading at T stat, on those wires one will may have 12V until the T stat contacts close when calling for heat.

[enblethen]

What is exact model of your furnace?
What is the issue with it?

[MT_BOB]

Yes, that is the circuit breaker, 2 red wires