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Noticed Pressure seemed high on Boiler gauge

pauljr Member Posts: 19
I was working in the basement and happened to look at the boiler temp & pressure gauge as I was walking by, boiler had just shutoff from heating zone. Circ pump, one of 12 was still running
Noticed temp was a little high 200F But pressure was just below 30PSI (2 story house with well water) I do have filter and water softener. Just purchased house 2 years ago, house was built in 2015, heating system has been serviced and mostly trouble free.

Checked boiler relief valve and yes it is a 30PSI valve. I though WOW!! this pressure way to close to max. I adjusted aquastat down to 175 (cooler water less PSI) and shutoff manual valve to the autofill.

I suspecting the autofill is not completely shutting off. I noticed the fill valve needle on top is set at 20. I think that is too high for fill??

I also went and got a screw on pressure gauge that you put on a boiler valve and installed on one of the circ pump isolation valve. Opened the valve and the new gauge reads 20psi on the zone vale. The zone valves are connected to a 2" iron pipe manifold going directly to the boiler, so the pressure should be about the same??

Could the boiler gauge be that far off??

I thinking a need to shut down system, let it cool and check pressure then drain until pressure is about 10 PSI.

BUT its very cold here right now, New Hampshire winter, I thinking just keeping a close eye on system until warmer weather. Maybe drain some water off using circ pump isolation valve port.

I also have indirect (superstore unit) I could have a leak in that coil, but I would hope that tank would last long then 17 years.

Also the Amtrol expansion tank may have gone bad.

Ideas / Advice?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited January 2023
    Are you doing this yourself? What repairs are you willing to, or are able to do yourself?
    The lower temperature is a good idea as long as it does not effect the heat in your home, or the Domestic hot water (DHW) in the Indirect.

    I would purchase a new Tridicator (boiler gauge) and a relief valve. The relief valve instructions indicate that you should operate it once a year to be sure the passage ways are clear and the valve is able to relieve over pressure. The reason I would have a replacement is if you do operate it and it fails, you can replace it right away. If you operate the relief valve and it fails to operate properly, by code, you can not operate the boiler if there is a faulty relief valve or no relief valve. So you can't just plug it temporarily to get heat.

    The reason for the replacement gauge is that you have a "Known Good" gauge that has a different pressure reading than your boiler gauge. The boiler gauge should be replaced with a "Known Good" or new gauge. The temperature may also be off by a little. Those gauges are not expensive and have been known to be incorrect more often than not.


    Call your Plumber or oil burner tech.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    EBEBRATT-Ed Member Posts: 15,353
    Could be a bad gauge or expansion tank or PRV.

    I would keep an eye on it and wait for a warmer day if possible. With the circs off the pressure on your two gauges should be the same.

    The expansion tank should be removed or the water side isolated and drained and then check the air pressure with a tire gauge. Should be 12-15 psi. 15psi is adequate for a two story house.

    Indirect coil leaking is a possibility.

    The only thing you can do is isolate 1 problem at a time to figure out the culprit.

    Make sure your relief valve (usually 30 psi ) is working
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    What makes you think the expansion tank os bad?
    What makes you think the indirect water heater is bad? They sometimes have 20 year or lifetime warranties .Call Amtrol with the model and serial number and see if there is any warranty left on the tank and internal coil.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • pauljr
    pauljr Member Posts: 19
    I have done a lot of work like this myself, just never seen 2 gauges read so different. If the new gauge on the circ port is accurate, then I am comfortable with 20 PSI. I know this gauge on the circ port is good, I just wasn' t 100% sure that that the circ port is = to boiler pressure, No sure how it could be less but wanted to get opinions of other. If this was summer, I certainly would shut down system, drain replace gauge and Pressure relief valve. System was serviced checked in August unfortunately the tech did not write down pressure reading, and I was too busy to watch him. Now everyone is busy with 'No heat" calls to come out and check my suspicions.

    In list of things that could be bad, I just listing what I have seen go bad in my 40 years maintaining apartment buildings. I am hoping nothing is bad here, except for the gauge.

  • hot_rod
    hot_rod Member Posts: 21,898
    I'd use a 30 psi, maybe a 60 psi test gauge. The lower the range, the more accurate. You can change the gauge on those hose bib set ups.

    What is the operating temperature set for? 200F seems a bit high?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • pauljr
    pauljr Member Posts: 19
    The aquastat was set at 195, the service probably set it at that temp in August. I do not find a 5 degree diff between aquastat and gauge an issue. I changed it to 175 which is the temp I typically set my boilers at. Baseboards are hot and house is comfortable. I have moved my hose bib gauge to 4 different spots in the system, 3 of the circ pump ports and the boiler drain valve. My new hose bib gauge does not go over 20 psi no matter where I put it. So, I am now thinking the gauge on the boiler is no longer accurate. The boiler is a Utica boiler, and the gauge sits on top, need drain system, remove smokestack and top sheet metal cover to get a wrench at the fitting under gauge. A real PIA. Thats a summer job, I have heat, so any help is not coming.
    I have a new 30PSI relief valve on the shelf, so it the one on the boiler does fire or get stuck open I have the part. I will pickup a new gauge Monday to have on hand ready.
  • MikeAmann
    MikeAmann Member Posts: 992
    I just found that my boiler gauge reads 6 psi high.
    Your autofill should be adjustable, so lower the setting to 12 psi.
  • pauljr
    pauljr Member Posts: 19
    MikeAmann said:

    I just found that my boiler gauge reads 6 psi high.
    Your autofill should be adjustable, so lower the setting to 12 psi.

    Do you mean you boiler gauge reads 6psi higher than another gauge on your system? (please explain)

    Yes, the autofill is adjustable, but according to the manual the adjustment can only be done before filling the system. Therefore, I will need to drain the system before adjusting to 12 psi and then refill.

    The fill valve I have is a Caleffi 553542A AutoFill .

    Thank you