A Honeywell Pressuretrol Controller is a device that monitors the pressure in a boiler. The Pressuretrol Controller will turn the boiler system off once the pressure within the boiler reaches a certain pressure. Once pressure in the boiler falls below a certain pressure the Pressuretrol Controller turns the boiler back on. The Pressuretrol Controller has two adjustment dials, the Main Scale, located on the outside of the controller and a differential dial located on the inside of the device. Setting and adjusting these dials depends on whether the system is a additive or subtractive system.
Determine if the system is an additive system or a subtractive system. The front panel of the Pressuretrol Controller will state either "Cut In" for an additive differential or "Main Scale Cut Out" for a subtractive system.
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Adjust the Main Scale set screw to adjust the amount of pressure required to break in or cut off the system. In an additive system, this is lower PSI range where the system is to cut in. You can set it anywhere from 0.5 lb. per square inch to 9 lbs. per square inch. On subtractive systems, the main scale screw sets the top PSI before the boiler cuts out. You can set this between 3.0 and 15 PSI.
Remove the outer casing of the Pressuretrol Controller to access the differential dial using a screwdriver.
Adjust the differential dial by rotating the small disc. The differential dial is the allowable difference in PSI compared with the Main Scale before the boiler turns on or off. The differential dial can be adjusted to 1 to 5 PSI. For example, in an additive system if the Main scale PSI is 3.0, which is where the boiler will turn on, the boiler will turn off between 4 and 8 PSI based on how the differential dial is set.