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Pressuretrol not working, plumbed correctly??

I have a question for the experts on here. Does this pressuretrol setup look correct to you? This is on a one pipe system, 500k btu boiler (big, big old estate home). I’ve had to replumb a lot of botched work. I’m sure the company who installed the system 5 yrs ago had zero idea what they were doing. Trust me, it’s a long story..... I’m sure of it.

So my issue with the pressuretrol now is that I’m cycling for too long. Then the first control (with the reset switch) will trip and shut the system down. I’d like to get a cut in/cut out switch in there that will help me cycle shorter, to give the radiators and heat exchangers time to get the heat into the house. 

The loop that the pressuretrol switches are on is full of water. I’m not sure I’m getting any pressure at the switches...well, yes I am, because the one trips.

cut it set to 1/2 psi
cut out set to 2 lbs

the gauge never budges.



  • Jamie Hall
    Jamie Hall Member Posts: 22,952
    A few things -- yes, that is a bit unusual, but it should protect the pressuretrols and gauge well enough. I'm not a bit surprised that the 0 to 30 psi gauge doesn't budge. It shouldn't. Until all the radiators are completely full, in fact, the pressure should be down around 2 to 6 ounces per square inch, if that, assuming that there is at least some main venting.

    I can't make out what the settings of the two pressuretrols are. The big one -- with the manual reset button -- should be set to around 3 to 5 psi. It's there for safety -- and no other reason. The other grey one should be set to around 0.7 psi for the cutin, and the differential wheel inside should be set to about 1. That will give you a cutout of 1.7 psi and a cutin of 0.7 psi, which should work just fine (you mention heat exchangers, though -- they may take a higher pressure).

    Now if that low pressure pressuretrol doesn't trip before the manual one, and they are set properly, there is something amiss with that specific pressuretrol.

    You say you want to have the cycles shorter. Ah... no. If the boiler is operating, steam is taking that heat out to the radiators, which in turn give it to the structure. If the boiler is not operating, there is no heat being given to the house (the residual heat from the radiators is, to a very close approximation, the same heat the boiler put into them to warm them up in the first place). If the thermostat is calling for heat, the house needs heat and the boiler needs to operate. Only in the situation where the boiler generates more steam than the radiators can handle do you need to cut the boiler off to allow the radiation to catch up. That situation is common enough, but doesn't seem to be the case here from your description.

    The thing to remember is this: the radiator can only put as much heat as the operating boiler puts into it.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    edited January 2021
    Set the manual reset to cut out at 5 or more PSI. It is there as a safety device, not an operating control. Next, set the pressuretrol to .5 and 1.5 and see if there is enough pressure to heat all the radiators. There should be.

    Finally, the 30# gauge is required by code for the boiler manufacturer to get the necessary approvals to sell the darn thing. If you want to know what is happening, you need to add a second gauge that is more accurate for the actual pressures you are operating with. Something that measures in ounces per sq inch. like 0 to 3 PSI with 8 or 16 hash marks between the numbers.

    But you only need that gauge if there are problems that you need to be solved. If everything is working, why do you need to know if the pressure is at 17 ounces or 22 ounces per sq inch? And what are you going to do about it if it is at 22 ounces PSI?

    Just my thoughts

    Respectfully Submitted

    If there is a problem you want to solve, What is the problem?
    (other than the manual reset control popping off) I gave you the answer for that!

    AND the weird loop of piping is to create a water seal to protect the gauge(s) and controls from raw steam overheating the delicate parts. So... Yea, it is piped OK

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • mattmia2
    mattmia2 Member Posts: 9,469
    it looks like the manual pressuretrol is set to 2 psig, so it is very ckose to the operating pressure, that is why it trips before the poerating control. take out the plugs and make sure that loop is clear too.
  • UnderwoodManor
    UnderwoodManor Member Posts: 6
    thank you!!! I’ve always been confused by the pressuretrols, but now I get it. I’ve raised the pressure of the safety switch up to 5lbs, and set the cut in/cut out at .5 and 1.5. Hopefully that does it!!
    EBEBRATT-Ed Member Posts: 15,346

    B4 you make any adjustments I would remove and clean both pressure controls and make sure the piping is all cleaned out. Black pipe is allowed for mounting controls if 1/2" IPS or larger which yours is. The 1/4 " nipples under the pressure controls should be brass

    The tee the pressure gauge is mounted on I would remove that plug and install a boiler drain valve so when the boiler is steaming you can put a hose on it (with caution) and blow the piping clean once or twice a year. Put a hose cap on the valve for safety when your done
  • neilc
    neilc Member Posts: 2,673
    check that the horizontal under the Ptrols and gage has some pitch back to the water seal loop,
    hard to say from the picture but is looks like it could be low at the right end,
    you would almost want to change that vertical nipple for one an inch or 2 longer just to keep the horizontal out of the water loop seal level,
    known to beat dead horses