Learn to adjust the Honeywell Pressuretrol controller
Measuring the pressure in a boiler is done using the Honeywell Pressuretrol Controller. This controller has the purpose to shut down the boiler once it reaches a critical pressure and to turn it on once the proper pressure is established. There are two adjustment dials within a Honeywell Pressuretrol Controller: the Main Scale and the differential dial.
To find if your system is additive or subtractive look at the front panel of the Honeywell Pressuretrol Controller and if it states “Cut in” it is an additive differential or if it states “Main Scale Cut Out” it is a subtractive system.
Set the amount of pressure at which the boiler shuts down or turns on. You do this by adjusting the Main Scale set screw. Adjust the Main Scale set screw to adjust the amount of pressure required to break in or cut off the system.
In order to access the differential you need to remove the outer casing of the controller with a screwdriver. Rotate the small disc in the differential dial to adjust it. This decides which is the allowable difference in PSI, compared with the Main Scale, until the boiler is turned on or off.