Honeywell M9174 modulation motors

lvrailroader_2004

Has anyone else out there besides myself ever had a Honeywell modulation motor come back down to low fire position, either for shutdown or to make the low fire switch for ignition, but the motor fail to stop at its set low fire position and continue 90° backwards? And when this happens, it usually jams up the linkage somewhere... usually either a reduced port gas butterfly valve, a gas butterfly valve with stops inside, or a linkage arm binding up against the burner housing is what generally stops the motor mid stroke going backwards that 90°. And woe be it if there's a Hauck oil metering valve connected to linkage attached to that mod motor... the metering pin inside the valve usually gets sheared off in the process. The first one I ran across, I honestly thought someone sabotaged the boiler. Now, about 6 of these incidents later, I'm pretty sure there's an internal fault in something... maybe the little potentiometers that set the stroke, maybe a feedback potentiometer. And of the 6 I've witnessed and taken care of personally, 5 were M9174C 1025's, and one was another model (not a M9174). Has anyone else had similar things happen with Honeywell mod motors? And has anyone figured out a cause for this?

Jamie Hall

In general there will be a limit switch in their somewhere — often a cam — which opens when the proper location is sensed, and if that switch sticks or fails to open, or there is a short in its wiring, you have the problem.

lvrailroader_2004

That's exactly what i figured as well. A coworker that has a background in controls looked at the motor I had torn apart. On the circuit board is what he called an encoder, it has a little gear that's driven off a gear nestled in just behind the high fire switch cam lobe, and that gear is attached to a little box... he said that's what tells the motor the exact degree it's at. Said likely the issue is with that , possibly being set too near the 0 degree mark. I haven't powered up this old motor that I've torn apart to see what it'll do.

lvrailroader_2004

EBEBRATT-Ed

Never had that happen. I thought they had limit switches inside to prevent this. The Honeywell motors are usually very reliable.

Guess anything can fail, but that is a bad failure to have, can certainly screw up a lot of other parts.