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Boiler pressure rising

leaking Member Posts: 46
Have a 30 yr old hw boiler, old pressure temp gauge and blow off valve just replaced, now pressure is at near zero cold, by the time it gets to 170 it's at 30lb and blows the 30lb relief valve, expansion tank valve is open, is something wrong with expansion tank? Is a 30lb safey relief valve to high a rating on a 30 yr old boiler, it's a small 2 story with boiler in basement, boiler has circulator pump


  • SWEI
    SWEI Member Posts: 7,356
    Do you have a tankless coil or an indirect?

    Have you checked the expansion tank?
  • leaking
    leaking Member Posts: 46
    Boiler pressure rising

    No coil , I don't know what indirect is, it's just a simple 30 year old Utica boiler. How do I check the expansion tank
  • SWEI
    SWEI Member Posts: 7,356
    Can you post a picture

    of the boiler and nearby fittings, valves, pumps, etc?

    Tap on the expansion tank with a screwdriver handle.  What kind of sound does it make?
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited April 2014
    Expansion tank

    If your tank has a valve on it, you can unscrew it and see if its is full of water, if its heavy its bad, I have used many methods of checking them, tapping, wobbling, checking the psi tap, trying to feel if they are heavy, all ways which have tricked me at one time or another over the years... Best way is to take her down and check it... They are generally easy to tell if they are bad if they are bad {I know that doenst make a lot of sense} but if they are bad then I can walk up to them and say yah its bad, but if they are good, I will double guess myself and just take it down to check and then put it back up if its good...

    As far as your over psi issue goes... Its one of the things in our industry that everyone attacks differently...

    I first check for positive shut off {even though you are saying it happens when it gets hot}, make sure the feed valve and pressure reducing valves are in working order.

    Next I check the tankless or indirect hot water tank {some people call it a boiler mate, boiler buddy, ect, its a tank that heats DHW with your boilers hot water}. If your boiler also makes DHW {domestic hot water for your faucets and taps} then there is a coil or tank somewhere that on one side of it is full of high pressure domestic/potable water, if this leaks it will leak into your boilers water supply and raise the pressure...

    Next if that all checks out is the expansion, when you heat this water it has to go somewhere, so we have expansion tanks, either a steel tank cylinder or an expansion tank with internal air bladder. The steel tanks need to be correctly installed and have the correct amount of air in them to work properly, the bladder style will have a shrader valve on the bottom that will let you pressurise the bladder.. Some guys do this differently but I put the exact same psi in the bladder as I run the boiler, so if my pressure reducing valve is set at 15 psi I make sure the tank has 15psi in it... Also these tanks need to be properly sized, too small is almost as good as not having it there and too big, well I don't know what that would do but I would rather have too big since the only down side I can think of is cost...

    So if the expansion tank is properly sized, has the proper pressure in its undamaged baffle, and is properly installed you can move on to the next issue...

    Pumping, you could have an issue with your pump size and location, I know its rare but I have seen people try to fix heating issues with LARGE pumps, these pumps can raise your pressure and or suck extra water into your boiler through your feed valve.....

    So after all of that is checked,

    your feed valve is working properly and positively shut off at your desired temp

    your boiler is heating to a stable temp {180* not 255}

    your boiler is not getting "street" pressure, there is no way for water above 15 psi to enter

    your expansion tank is sized, installed, and pressurised correctly in working order

    your pumps are sized, installed, and working correctly

    if you can still watch your psi raise to and over 30 psi opening your relief valve, then you found a problem that I have never seen before...

    I have had techs call me from other companies {and my own} and say " I don't get it, I installed a brand new ball valve on the feed and shut it, I installed a brand new ex60 expansion tank and set the psi perfectly, I shut the tankless rite off with brand new ball valves, and its still pops the prv off"??? I take a ride over and look at the piping, there is the culprit a check valve in the header and one bwrds built into the circulator locking out the expansion tank...