Weil-McLain steam boiler psi too high

puck8605

Hi All -

First-time post. I have a Weil-McLain steam boiler that was installed two years ago by the previous homeowner. The pressure gauge consistently reads at 2.25PSI even when the boiler is off and will raise to 3.5PSI on days that are around 20 degrees. The cut-in has to be set at 2.25 PSI or the boiler won't run--I know it should be set as low as possible.

I installed a Barnes & Jones Big Mouth Vent and have carefully dialed in my radiators with a mix of Gortons, one Varivalve, and one Honeywell thermostatic vent (which is quite loud when the PSI gets too high).

It's a one-pipe system with three baseboard fin radiators on the first floor, three fairly large cast radiators on the second floor, and one small cast radiator on the third floor. I had to turn off a massive radiator in the garage because it was cracked along with a small baseboard fin radiator in a bathroom. I also removed two small cast radiators in bathrooms and opted for electric heated floors.

Could the boiler simply be too big? Am I missing something? Is there anything I can do? Appreciate the input.

-Andy

Jamie Hall

That gauge is out of calibration. If it sits at 2 plus psi when the system is cold, that's what it's thinking is zero. The actual running pressure is more like the registered high pressure minus the value of that false zero reading, or around 1.5 psi. It would do no harm to add a 0 to 5 psi gauge to the system (you have to keep the existing gauge).

dabrakeman

First of all there is no way it should read 2.5psi when the boiler is off. Check your pigtail and make sure it is cleaned out so the gage and ptrol can sense actual pressure. IF good take your gage off and see if it is zeroed.

puck8605

Ok, thank you. I will check the pigtail and report back.

exqheat

Indoor reset for steam runs systems at actual minimum pressures and run times to reduce fuel use.

mattmia2

Jamie Hall said:

That gauge is out of calibration. If it sits at 2 plus psi when the system is cold, that's what it's thinking is zero. The actual running pressure is more like the registered high pressure minus the value of that false zero reading, or around 1.5 psi. It would do no harm to add a 0 to 5 psi gauge to the system (you have to keep the existing gauge).

If the pressuretrol is also needing to be at that pressure I'm thinking the pigtail is clogged and the gauge and pressuretrol are actually at that pressure. Look at the differential dial inside too, it should be set to its minimum setting which is 1.

AdmiralYoda

Those 0-30psi gauges are notoriously inaccurate, especially near the limits. The 30psi is required per code but it would be very beneficial to install a 0-2 or 0-3psi gauge in addition. Set the Pressuretrol to 1.5psi with a 1psi differential, about as low as it will physically go.

It is kind of like having a 400mph speedometer on bicycle. It will barely budge and it will be near impossible to know your exact speed.

Your next step is to calculate the EDR of your radiators. It is simple once you get your arms around it and the people here love to help. Only then will you know if your boiler is oversized...which it usually is.

puck8605

The gauge is indeed faulty so I ordered a new one. The pigtail wasn't clogged but the water in there was very dirty so wondering if that could have been the culprit. I also confirmed the differential is set to 1.

After cleaning the pigtail, I turned down the pressuretrol to just below 1PSI as the boiler was running and it didn't shut off, which is a positive sign. Hoping that solves the issue.

Is it worth upgrading to a Vaporstat or is the pressuretrol sufficient for a system like mine?

TonKa

puck8605 said:

Is it worth upgrading to a Vaporstat or is the pressuretrol sufficient for a system like mine?

If your system is as described, an upgrade to a vaporstat is not worth it in my opinion. YMMV.

pecmsg

I disagree. A vapor stat with a low pressure gauge is worth the investment. 

mattmia2

A vaporstat would be better but wouldn't be the necessity it would be in a 2 pipe vapor system.

AdmiralYoda

Figure out your EDR and the steam capacity of your boiler. If it is ridiculously oversized it will cycle like crazy with a low pressure Vaporstat. My boiler is about 40% oversized and at about 8oz my radiators are full of steam and the pressure starts to climb rapidly. I have my Vaporstat set to 12oz just to give it some overhead.

The pressuretrol is now the backup and I've installed a 15oz gauge.

I rarely cycle on pressure unless I use a setback or it is very cold out.

TonKa

pecmsg said:

I disagree. A vapor stat with a low pressure gauge is worth the investment. 

No biggie. People will disagree.

Vaporstats are not cheap. For a 1 pipe system which seems to only build significant pressure when it's close to design days, what kind of guarantee of savings could be seen by cycling the boiler between, say, 4 oz (0.25 psi) and 12 oz (0.75 psi) with a vaporstat vs the typical cycling with a pressuretrol of between 8 oz (0.5 psi) and 24 oz (1.5 psi)?

puck8605

The plot thickens. The boiler was working great yesterday with the cut-in set at .5. The radiators were filling with steam and the vents were no longer hissing.

However, at some point at night, the boiler stopped firing and I had to adjust the pressuretrol to just above 2psi again. My house was 5 degrees below the set point and the boiler was cool so there wasn't any pressure in the system. Could this be a bad pressuretrol?

Jamie Hall

Assuming that the pigtail is clear, all the way into the boiler and all the way to the pressuretrol...

Yes it could be a failing pressuretrol.

puck8605

Confirmed that everything is clear. Looks like I'll be ordering a replacement.

dabrakeman

Well, the pressuretrols also are not very accurate so you may want to play with it a bit more. Just because it failed to let the boiler cut back in it may just mean you are set a tad too low. Mine is balanced on a razors edge to cut out at about 1.75psi and still allow cut-in which was the best I could do to not get into your same situation where it will not reliably cut back in. Guess what I am saying is you could order a brand new pressuretrol and if trying to achieve an exact minimum 1.5psi cut-out (you will need your 3psi or 5psi gage also to determine this) you may end up the same as you are with your current pressuretrol.

JUGHNE

If you crank the indicator down too low it can become disengaged....you run out of threads on the screw. May not restart in that case.

Long Beach Ed

As brakeman mentions, pressuretrols aren't very sophisticated instruments, and their reliability on the low end of the scale isn't optimal. Reliability has gotten worse since these things are being made off-shore with mechanical switches these days. They make "Vaporstats" for reliable operation below a pound. But as Tonka suggests, at its high cost, a Vaporstat probably won't give you a return on your dollar unless, perhaps if your boiler is greatly oversized.

Usually the wasted few steam ounces of a higher setting doesn't translate to many dollars of wasted fuel. Pressure rises very quickly once vents close.

I'd find the lowest reliable setting and bring it up a little above that for a safety margin. If you're not happy with that, look for a better quality control or invest in a lower-scaled Vaporstat.

mattmia2

If I were replacing it I would get a vaporstat. The cost difference isn't that much. I would also add a 1-3 psi gauge teed in with the rest.

Chris_L

You might need a new Pressuretrol. But more likely, yours just needs to be calibrated.
See:https://forum.heatinghelp.com/discussion/149944/i-figured-out-how-to-calibrate-a-pressuretrol
You'll need a low pressure gauge to check it. And don't set the cut-in too low or it won't reliably turn back on.

puck8605

Thanks, everyone. You've all been incredibly helpful. I ordered a low-pressure gauge and will attempt to calibrate the pressuretrol before adding a vaporstat.

puck8605

Update on the project. I ended up adding a vaporstat and low-pressure gauge. I know there's some debate about vaporstats on a one-pipe system but I like the idea of dialing it in exactly where I want it to be.

The pressuretrol is not calibrated correctly, however, I left it as is since I know it cuts off at around 3.25 PSI and will use that as a backup for the vaporstat.

I did have some short cycling initially with the vaporstat since the boiler had to recover from a 6-degree setback from when the boiler was off while I was making the modifications--I have an old brick house that needs some insulation work.

Lastly, I discovered that my thermostat was not meant for a steam system so I upgraded to a Honeywell FocusPro and set it to 2 CPH. I have fin tube radiators on my first floor that don't hold heat at all so 1 CPH doesn't work.

Overall, the system seems to be operating nicely. The temperature seems more balanced and I'm getting far less hissing and noise from my radiators. My next upgrade will be to swap out the fin tubes for convectors but that'll have to wait for next season.

Appreciate all of the advice on this thread and the many other threads on this forum.

exqheat

What gauge wire did you use? Minimum 18.

exqheat

shouldn't there be pigtails on each pressure control, well above potential water levels?

puck8605

exqheat said:

What gauge wire did you use? Minimum 18.

It's 18-gauge wire. I saw examples of this setup on other threads with single and dual pigtails and opted for the single. The pigtail is about 6 inches above the water line, which is where it was originally installed.

Jamie Hall

exqheat said:

shouldn't there be pigtails on each pressure control, well above potential water levels?

The piping shown there provides ample protection.