Goodman GMV95 Error Code 5

Bouwwhuis2000

My 2 year old Goodman flashes error code 5 "shorted Flame sense circuit"
Power reset returns the furnace to normal operation, for a day or two.
Microammeter in series with the flame sensor wire shows 2-2.5uA while burner is on, and zero when burner stops.

There is no short! The porcelain is clean and like new.
No there is no lingering flame.
Yes the Flue is clear
Yes the intake air is clear
Yes the drain systems are clear.
Yes the filter is new.

I would call a service guy, but the first thing he will do is reset the furnace, replace a perfectly good Flame sensor, declare it fixed and take a walk. A day later it will be flashing again and the next visit will likely declare a defective control board.

I have to be missing something, Any ideas out there?

PS it has flashed code 3 once or twice,( vacuum switch) but that seems to go away by itself.

yuri

Is the furnace and board grounded properly. Check for continuity to a copper water line from the furnace. Use a cheater wire from the water line to extend your meter leads (trick of the trade). Check the grounding of the board to the chassis, make sure the board mounting bracket screws are tight. Make sure nothing else is on the furnace circuit. Have seen lots of DIY wiring with lights/rec rooms on the furnace circuit. If you have aluminum wiring from the panel to the furnace replace it with copper.

Bouwwhuis2000

Ok will check grounds. It does have a 10ga wire from the copper cold water bonded to the incoming gas line.
Will run a good ground to the metal holding the board. Anything is worth a try, thanks.
Currently, it has been running all day with no problems. It only malfunctions at the end of a heating cycle.

Tator1076

Check the fan limit. Also check if the bar fitting from pressure switch to draft motor is clear.

Bouwwhuis2000

There are no fan limit switches, two manual reset overtemp sensors on the fan cage, one either side. Neither one trips. Since they are in series with 3 other heat limit sensors, they are not likely the cause, but I will recheck for loose wiring.

Fan is timed for 150 second run after the burner stops. It is not controlled by a low temp sensor.

Will check hose fittings again, but I was able to blow through all hoses easily. Thanks for your ideas.]
Bill. PS Konked out again this PM. Even changed the batteries at the
Aprilaire thermostat out of frustration.

Tator1076

You need to check voltage from pressure switch to gas valve to make sure you are getting 24 volts. Sorry hate to say sounds like 24 volts is dropping out some were and need to fine it.

Bouwwhuis2000

Well Now I have to wait for it to crap out again, has been running for 36 hours with no errors. Keep the suggestions comming, I appreciate the help !!!!! All ideas welcome. Bill.

Marty S.

Your flame sense circuit is the board,ground and the flame sensor. Ground is good, flame sensor good so that leaves the board. It's under warranty so get a new board.

beenthere

You got a vent or drain problem.

A pressure switch can open and close quick enough. That the board won't respond to it with an error code. But the gas valve will close. And eventually. You get a flame failure code.

What size furnace. What size vent pipes. How long is the run. Do you have proper slope.

Bouwwhuis2000

2" ABS 15 ft run. NO problems for 2 years so why now? Have checked for free flow of air, and for obstructions, I even vacuumed the intake. I do have a fibre optic video inspection camera, I should stick it in the pipes.

Condensate runs freely, pulled hoses and checked them.

Thanks for the ideas.

beenthere

So what size is the furnace. BTU???