Pressuretrol cutting out too late?

jweob

I just cleaned out the pigtail on my boiler - it was totally jammed with sludge and the pressuretrol wasn’t doing anything.

After cleaning it out I added a new pressure gauge because the existing one was suspect. I then fired the boiler. My cut in is set at 0.5 and differential at 1 psi, so I expected a cut out at 1.5 psi. However the new pressure gauge was reading 3.4 psi when the pressuretrol cut out. Is it expected that it is so inaccurate? Is there a way of calibrating it? I am already at the minimum setting.

jweob

This is picture of pressuretrol with pressure gauge in background

109A_5

Hello @jweob,

Before I tried to calibrate my pressuretrol I would get a third opinion. It is probably the pressuretrol that is not correct but I would want to be sure.
Testing the Accuracy of Honeywell Pressuretrol
https://youtu.be/mE1-QuUx4_c

pecmsg

Trust the pressure gauge not the control gauge. 

mattmia2

With about 10 ft of tubing you could make a water manometer and get a second opinion.

dabrakeman

Advise offered to me from @Fred 7 years ago. Worked perfectly. On same settings got my 3.5psi cutout down to 2 psi (since have found ways to avoid ever reaching that cutout). As it says go in small increments. If go too far the boiler will not reliably cut in.

From @Fred: 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.

mattmia2

You should probably put a drop of loctite or nail polish or glue on it after you are done since the loctite is likely the only thing keeping it from turning on its own with use.

SteamingatMohawk

@mattmia2 Good comment, but

3.4 psi x (1/(0.435psi/ft)* = 7.8 ft of water column or ~94 inches of water column.

If the water line is 2 ft above grade, then the top of the water column would be almost 10 feet high. So, the question becomes how high of a pressure can be measured in a typical basement (assumed) 8 feet high?

Back calculating 6 feet of water x 0.435 psi/ft of water is 2.6psi.

1 foot of water column is about 0.435 psi is what I was taught many decades ago.

mattmia2

My assumption was that you could work out which one was wrong before you built enough pressure to blow the water out of the tube. You are really only interested in if it is actually going above 1.5 psig or not.

BobC

If you use loctite be aware there are different grades that range from welded to mild. Use the milder strength so you don't round out the 0.05" hex set screw. Glyptal or a drop of nail polish are excellent choices as well.

Bob

109A_5

If @jweob really wants to know the actual cut in and cut out pressure of the original Pressuretrol calibration using the Manometer and the basement height is too low just extend the clear tubing part of the Manometer with a garden hose to the basement stairwell.

1 PSI to water column [inch] = 27.6799 water column [inch]

jweob

Thanks for all the advice! I have a second pressure gauge I am going to install and if that confirms the cut out is too high I will follow @dabrakeman’s instructions to adjust the pressuretrol

jweob

@dabrakeman 's instructions worked like a charm. The second pressure gauge confirmed that the cutout was too high, but adjusting that screw 1/2 a turn brought it back to 1.5 psi cutout.