I figured out how to calibrate a Pressuretrol!

Fred

I don't know if anyone else is interested in calibrating their Honeywell Pressuretrol but after tinkering with mine, I finally figured it out!

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 to much, a fraction of a turn goes a long way towards getting it adjusted where you want it (not even an eighth turn). You may need to play with it to get it exactly where you want cut out to be but at least mine won't run pressure up to 3 Lbs when I have it set to cut-out at 1.5.

nicholas bonham-carter

interesting procedure

Thanks for this tip. But if you could get it to go to a lower range, that would be even more interesting!

I'm sticking with my vaporstat!--NBC

Fred

Not a Vaporstat for sure

I didn't mean this was as good as a vaporstat. I may end up putting one on my boiler also but for those of us (and there are a lot of us) who still have Pressuretrols and have not been able to get them to act like a control device, there is a way to get it to cut out at the desired setting. My boiler typically runs at 7.2 oz. in a normal cycle but when it's below zero outside and I want to raise the indoor temp a couple degrees, to have it cut-out on pressure at 1.5 lbs (where I have it set) instead of it running all the way up to 3 lbs before the Pressuretrol cuts out is a big first step to getting things right.

SWEI

Assuming your description is accurate,

it appears that Honeywell has a serious QC problem (as opposed to an actual design defect.) This could be a good thing.

BobC

Monitor it

That adjustment can work but sometimes it causes the pressuretrol to trip but never turn back on. Monitor it for several heating cycles to make sure it's working ok.



Bob

Fred

Been Watching it

I have been watching it for about 10 cycles now. The first cycle I adjusted it to much and it cut-out at about 12 oz. I turned it back a bit and set my thermostat for about a 6 degree rise and watched it as it cycled and made minor adjustments until I got it to cut-out right at 1.5 lbs. watched it cycle several more times and it cuts-out within an ounce or two of the 1.5lbs. cut-out, which I think is about as accurate as a Pressuretrol will get.

gerry gill

good job Fred,

i do seriously believe that honeywell has a QA problem with these controls. But you did good figuring that out.

Fred

Thanks!

Thanks Gerry. That means a lot coming from a Pro like you!

LionA29

Great Job @Fred.
Thank you for sharing !!

ChrisJ

@Fred I missed this thread.

I figured it out too, size the boiler properly and don't worry about the Pressuretrol's setting.

Fred

ChrisJ said:

@Fred I missed this thread.

I figured it out too, size the boiler properly and don't worry about the Pressuretrol's setting.

Not everybody is blessed with your brain power @ChrisJ

ChrisJ

Fred said:

ChrisJ said:

@Fred I missed this thread.

I figured it out too, size the boiler properly and don't worry about the Pressuretrol's setting.

Not everybody is blessed with your brain power @ChrisJ

I know, right?

JWise

So if your boiler is indeed oversized, what is optimal pressure you are looking for ? What should I be looking for during a cycle.

EBEBRATT-Ed

Try and stay under 2 lb. The lower the better but try and avoid short cycling. You have to keep the pressure low enough to keep water out of your dry returns. Water will rise up 2.31feet/psi above the boiler water line.

Like everything in this business there is no direct hard answer. Always a compromise

Fred

@JWise , When I started on my system, I was hoping to stay under 1 PSI. By the time I got done, adding the ,main vents I needed, calibrating the Pressuretrol, and fine tuning everything that needed correction, my Pressuretrol once again became a Safety Device and not a Control device. I was fortunate that while my boiler was/is over-sized, my risers are 4 ft above the water line and I have a 5" header. Those things helped keep the steam dry and, I believe, aided with the Pressure issues.
Before adding a 0-3 PSI gauge, my 0 - 30 PSI gauge barely moved but I was actually running at 7 PSI! The boiler ran almost constantly and the house was still cold. Radiator vents hissed like they were about to fly off of the radiators. I could hear gurggling and as @EBEBRATT-Ed said, above, the water in the boiler would back out into the wet returns. I use to use a 4 degree set-back which I stopped doing because it would literally take hours for the boiler to bring the house up to temp (and it is over-sized).
I have since added a 0-16 ounce Vaporstat with the cut-in at 4 ounces and the cut-out at 12 ounces. I rarely ever have a heating cycle over 2 ounces of pressure and a heating cycle is about 20 minutes. On Design Days (0 degrees) I may have one or two heat cycles where the pressure reaches the 121 ounce level. I never have more than two short cycles per heating cycle and rarely more that two or three cycles during the winter when that occurs.

Dave0176

I made a little simple rig up to test pressuretrols. It works perfect and I’ve yet to come across a factory pressuretrol that’s set right.

guzzinerd

Very helpful older thread.  Just wanted to just add that on my L404F, the adjustment screw is a small flathead accessable behind round chrome hole cover on back.