Amana furnace- flame sensor keeps failing about once monthly

carlc

Hey folks, I’ve been working on Amana AMH80803BNBB furnace for the past 3 or 4 months. The furnace is from 2016. Starting this winter, about once a month we’ve been having flame sensor failure issues. We’ve cleaned the sensor, replaced it with an oem and tried a different manufacturers flame sensor. Replaced the control board as well. When the sensors fail they are testing at 0ua. When a new sensor is installed it tests around 3ua. There is not excessive dust/dirt or detergents near the furnace. Any ideas? Thanks

JUGHNE

The flame sensor is only half of the electric circuit.
The grounding path is the other half.

Do you have a separate ground wire from the burner to the ignition module? I would add one IIWM.
The ground path may be thru the burner or pilot tubing if any.
Also the metal plate behind the pilot flame needs to be in place and clean for the process to work reliably.

It could be that every time you change the FS you re-establish the marginal grounding circuit. Then it eventually fails for a variety of reasons.

unclejohn

Might as well replace sensor wire as well. And check ground wire to furnace from panel.

Mike

Have you checked your flame signal? How many microamps?

HomerJSmith

In reference to unclejohn's post, I would check the polarity of the the AC voltage at the house connection (receptical) with a GB polarity tester and make sure the wiring (pigtail?) to the furnace is correctly connected to the furnace. Flame rectification current can be affected by incorrect AC polarity. Also, connect a good ground to the burner tubes to the gas valve to the ignition board.

JUGHNE

Every troubleshooting guide says to check the AC power polarity.
I can see this on initial start up. It is either right or wrong.
But is it a potential problem that the polarity could be wrong, working most of the time for years and suddenly shows up?

I am asking the question not criticizing any suggestions.

I never have seen reversed polarity work for a long time and then suddenly be an issue.

HomerJSmith

It was just a thought and is one of the things I would normally check, it is quick and easy to do. It is a strange universe to be sure, but one thing you can take to the bank is that it is a cause and effect universe.

Does the ignition module have a good ground? If you have a current drop from 3ua to 0 ua, that current has to go somewhere. Either the ignition module is bad, the wiring between the module and probe is grounding out, the flame isn't producing a path for the current to ground, or the ground isn't getting back to the module. A bad HV cable?

Do you have a sound pilot flame? How can you measure 0ua without an operating flame or do you measure a good 3ua and then the current goes to 0ua and the furnace flames out?

If a new control board has the same problem, it's not the control board per se, I would think. Flame rectification is a circuit. Look at each connection in that circuit, from the control board back to the control board.

On one occasion I had to run a ground wire from the pilot assembly back to the tie on the gas valve which was tied to the ignition module ground.

If you solve your problem, I would be interested in your solution.

HomerJSmith

You don't think that the flame is impacting the probe ceramic and leaving a deposit on the ceramic and providing a ground path from the probe tip to the metal holder thereby grounding out the rectification current? I would clean an old probe's ceramic with comet and a scotch sponge really well and see if that failed probe works like a new one.