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Boiler has too much pressure

A have a boiler that is building around 25 psi of pressure and spitting out a little bit of water from the pressure relief valve. The backflow preventer is installed and also the pressure reducing valve (set at 12 psi). The tank (air scoop) has/is known to have the correct pressure (12 psi) and to have no leaks. I followed instructions on how to charge the tank. It was definitely low on air. Now at the right level. The pressure relief valve was changed out about 2 years ago. The pressure at the boiler through another gauge reads 20 psi.  The boiler is in the basement. There are 4 pumps. Here the sequence:

1) Pump for radiant heat through the subfloor (about 1000 feet of 3/8" pex) on first floor (covers about) 1,200 square feet

2) Pump for the hot water holding tank (run is about 5 feet supply and return)

3) Pump for the 1st floor (Radiators) only

4) Pump for the 2nd floor (Radiators) only

I read a post somewhere indicating that if you have a 2nd level the psi or pressure will increase from 12 psi to 18 psi and if you have a 3rd floor to about 24 psi reaching my level where I am at? 

Questions: Can a backflow preventer be causing too much pressure? Can a pressure reducing valve be causing too much pressure? Can an expansion tank be causing too much pressure?

I do have insurance and the gas company stated that the pressure is normal. Although everywhere I am reading indicates that the pressure should hold between 12 psi-12 psi.

They do cover certain items under the contract if defective and other items are extra. I can order the parts if extra and have a friend install them.

Please advise? Thank you.

Silver Cheetah


  • pipeking
    pipeking Member Posts: 252
    thers a couple things u can do

    u want to check to see if the PRV is not faulty. bring the pressure down to where is needed for your system them shut off the feed to the boiler; if the pressure still rises then it it's not your PRV its somthing else. fyi, the back flow does not have any affect on pressue. so now u want to look at your exp. tank, tap it does it sound hollow, it should. the only way to check the pressure in the exp. tank  is to remove it from the system presure. if u find that it's ok then move on to the tanklesscoil (if u have one). that could be leaking into the boiler and raising the pressure. try this stuff first, and let us know how u make out.
  • SilverCheetah
    SilverCheetah Member Posts: 43
    Too Much Pressure

    The main line from the township from outside comes directly into the holding tank (hot water). From this point there is a shut off valve and here is the sequence. The backflow preventer then the PRV moving on to the expansion tank. They all work up to the return side of the boiler for the heating. There are 2 flow control valves for radiant and hot water tank. The pumps I am assuming push water down into the boiler and up to the pipe out of the boiler and to the piping, zones, etc.

    Question: Should I shut off the valves before the backflow on the tank and the ones after the tank. I can post a picture if necessary?
  • SilverCheetah
    SilverCheetah Member Posts: 43

    I shut off the valves and lowered the pressure to about 15 psi. Then ran the system for 5 minutes with valves off. After 5 minutes I opended the shut off valves and now the pressure has stayed under 20 psi (assuming guage is correct). System ran for one hour and pressure did not change. Could something be getting stuck?
  • SilverCheetah
    SilverCheetah Member Posts: 43
    Have I masked the situation ??

    After the last post, my pressure has gone back up to 25 psi and kicked out a little bit of water. So what I did is turn the PRV counter clockwise 4 turns after releasing some water from the boiler (which the pressure dropped to 15 psi). Now it seems that this has kept the pressure at 15 psi which I am comfortable with. Everything states about 12 psi but I can not turn the screw too many more times before I feel that the adjusting screw on the PRV will fall out. 

    So have I just masked the situation?  Should I shut off both valves and test the PRV with a gauge (up top)? Please see pictures?

    Thank you.

  • pipeking
    pipeking Member Posts: 252

     down to the pressure needed for your system prolly 12-18psi. once u do that shut off the valve that feeds the boiler for a day or 2. if the pressure doesn't rise we found the problem. so u say the pressure from the road is high how high? you might need a pressure reducing valve for the house to bring it down to a manageable pressure. u might also need a new prv 4 the boiler from being over worked.
  • SilverCheetah
    SilverCheetah Member Posts: 43
    The boiler is staying at a constant 15 psi

    As I mentioned previously. I do have a PRV. I had adjusted the adjustment screw counterclockwise 4X and the pressure dropped from 25 psi to 15 psi. Although today as the heat turned on the pressure dropped too much, almost down to "zero" pressure, so I turned the adjustment screw clockwise 2X. If I shut off the valve/water that feeds the boiler (which I will have to find out where it is), will that affect any of the water that is going to the holding tank? I could never get a good grasp on this.

     I do understand that the water in the heating system, whether radiant or pex tubing will circulate back to the boiler, into the boiler heating element and up through the pipe. I am assuming the circulator pump I have does the same thing. I will post more pictures if need be. Where exactly is the valve that shuts off the boiler. Is it before the backflow preventer or after the PRV. I have 2 shut off valves. The one prior is coming off the holding tank. The one after seems to shut off the water to work on the PRV. Again at this point the boiler is holding steady pressure.
  • SilverCheetah
    SilverCheetah Member Posts: 43

    The township increased its water pressure to meet the demand and certain codes. So the PRV needed to be adjusted.  The counterclockwise 2X did the trick. 15 psi and holding steady. The range should be between 12-18 psi (from what I have read) because of the 2nd floor hot water and circulator pumps. Also the expansion tank is at the right psi level (12 psi). Additionally I tested the pressure from an open valve at the boiler and the readings are the same.

    If I need to raise the pressure higher someone please tell me. Thank you.

    Silver Cheetah
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