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Pressuretrol Calibration

dabrakeman Member Posts: 248
Had a question on an earlier thread posted by Fred. Relative to the instructions below what is meant by a 1/32" turn. Is 1/32 of a rotation meant?

Reason: On recoveries my system had been reaching ~3.5psi even though the differential dial was set on one and the cut in at lowest setting (0.5). I made based upon the advise a small adjustment of about a little less than a quarter turn and it seemed to bring the displayed max pressure on recoveries down to just under 3psi. I had an "annual inspection" from my installation company this Wednesday and mentioned the fact that it seems when set as it is it should cutout closer to 1.5psi or 2psi. After cleaning the pigtail the technician ran a cycle and as the pressure was rising past 2psi he adjusted the screw until it shut the burners off. I guess he turned it a good 1-1.5 rotations clockwise (I figured he knewe what he was doing). I didn't witness any issues the next and the house heated fine. Friday evening the house starts getting cold and I go down and see the boiler off even though the stat is calling for heat and everything is getting power. Why the issue didn't arise immediately the morning after the adjustment I don't know but bottom line it appears the screw was way over adjusted. I think I have it adjusted back better now but given the delay in the issue last time I will wait a few days to make judgment. The reason for this post is simply to get a clarification on the 1/32" instructions in case others try to make this adjustment. So, should be short thread.

From Fred's previous post:

Most of us use a 3PSI gauge from WIKI. The supply link is below. I would first check the Pigtail (looped pipe) the Pressuretrol is mounted to. They often get clogged andd the Pressuretrol can't sense the actual presure. Take it off and clean it out good. If that doesn't bring the Pressuretrol into a reasonable range, following is the procedure to recalibrate it:
Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with). You may need to play with it to get it exactly where you want cut out to be.


  • Fred
    Fred Member Posts: 8,518
    @dabrakeman Yes, turn that screw in very very small increments and test the cut-out each time. A very small amount of turn goes a long, long way, as you have learned. fortunately, the fix is simple. Start turning it back until you get the calibration right.