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

Different places.
Easiest from your photo, is from either side of the circuit breaker to ground. Metal housing should work.
Better place is on left side not shown in photo, is incoming power. Not the blue wires as they are thermostat leads. Should be red and yellow leads.
See page 9 figure 6
manual

enblethen wrote:
Different places.
Easiest from your photo, is from either side of the circuit breaker to ground. Metal housing should work.
Better place is on left side not shown in photo, is incoming power. Not the blue wires as they are thermostat leads. Should be red and yellow leads.
See page 9 figure 6
manual

Thanks, but that link is for a different furnace. I have the manual for mine with wiring diagram. If I unplug the input to the board to get at the ends of the wires (also yellow and red), the furnace can't run and with it plugged in I can't get at the ends of the wires. The board is in a slot I can't get at with the meter leads. Not sure I can pull the board out enough while the furnace is running.

Is the circuit breaker the one top-left?

Yes, that is the circuit breaker, 2 red wires

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

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.

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?

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?

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?

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.

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.