Working on a Rheem natural gas furnace. It's got the "jet" type burners.
Four burners. 80 percenter.

The inducer blows, the HSI heats, the gas lights. And lights all the way
across. About a second later, the gas shuts off. And, the whole thing goes
through the routine again.

The call came in Friday about 6 PM. Didn't have a sensor rod, so Monday I
bought one.

Now, even with a new sensor rod, and a new grounding screw, it's still the
same. Fires for a second, and then shuts down.

The furnace is a 1999 model now. Has had essentially no maint except for
filter changes.

I checked the ground to neutral at the furnace (less than one ohm) and the
connection between the terminal and the molex connector where it comes off
the main board. Also less than one ohm. Then checked the ground screw from
the sensor rod to the 110 VAC ground. Again, nothing.

Guess the only grounding thing I didn't check was that the ground wire from
the 110 VAC was connected to the case of the furnace. Is that relevant?

What else to check, or is it time to replace the board?

--

Christopher A. Young
Do good work.
It's longer in the short run
but shorter in the long run.
..
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