HONEYWELL MODULATING MOTOR

Weil

Recently went to a customer with two 42-year-old firetube boilers with Power flame C burners. They are controlled by a Heat timer panel. Number 1 boiler was firing steady state. But number 2 boiler after warming up for about 15 minutes on high fire would start to hunt from high fire to low fire continuously. The modulating pressure control is new. Thinking it is a bad potentiometer in the mod motor. Any thoughts are appreciated.

EBEBRATT-Ed

Honeywell use to make several L91 pressure controls. Some just had a modulating setting. Some had the modulating setting and a "differential. The #s used to be L91A with no differential and L91B with differential if I recall correctly.

I seriously doubt it's the motor. I would say widen the differential if you have an adjustable control. If no you may have to change the control.

Also, when the L91 modulates and constantly hunts it will tend to burn a spot on the potentiometer in the L91.

To test it you could buy and adjustable potentiometer and wire it in place of the pressure control and see how the motor responds.

#30112A @ Supply House.com. But the price is outrageous.

If you disconnect the pressure control and use a jumper to drive the motor up and down (R-B then R-W) the motor should be good. It is usually the control.

Weil

First of all thank you for your feedback. I purchased the potentiometer. Worth the money for sure. I replaced the L91B and all is well.

EBEBRATT-Ed

Glad it worked.