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High pressure in boiler

PMV Member Posts: 2
I have a oil burner with a  separate 20 gallon storage tank . The pressure in the boiler is about 29psi and the relief valve is always leaking . How can I lower the pressure? or What could be causing the pressure to be high? Thanks for your help


  • Steamhead
    Steamhead Member Posts: 16,736
    Could be a number of things

    and this is best handled by a pro. Where are you located? Have you tried the Find a Professional page of this site? 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • PMV
    PMV Member Posts: 2

    Thanks. I was told by two different professionals it was the storage tank leaking.

    I was just looking to see if anyone had another idea. the tank is getting changed tomorrow.
  • Mac_R
    Mac_R Member Posts: 117
    Storage Tank?

    If there is high pressure in the boiler it is because of three main reasons.  There could be many more. 

    the easiest thing to check is the extol tank.  I think that is what you are calling a storage tank.  If it is a little gray or some times green tank that has a valve stem on the bottom remove the pressure from the system by shutting the water off to the boiler and then popping the relief valve or draining a little out using the boiler drain at the bottom of the boiler. after the pressure reads 0 use a tire gauge and see if it is set at 12 PSI.  if you get water out of it then it is bad and needs to be replaced.  if it reads nothing use a bicycle pump and pump it up to 12 PSI. 

    the second thing is some times the auto fill or pressure reducing valve can get stuck open and it will over fill the boiler.  try removing the pressure from the boiler like before.  then allow the boiler to fill to the proper pressure and shut off the water supply to the boiler.  if the pressure stays where it should then it is a problem with the auto fill. 

    the third thing it could be but this is a rare occurrence is air in the system.  what happens is air gets into the system and displaces the water.  then because you can not compress water the pressure goes through the roof.  try purging the system of air.  how to do that depends on who installed the system. 

    if you don't have a tank like I described before.  then most likely it is a big round tank with a boiler drain and another pipe most likely 1/2" or 3/4" sticking out of it.  look at it.  if it is dripping then it needs to be replaced.  if it is not leaking then it should be fine.  when is the last time you drained it?  hook up a hose to the boiler drain on the tank.  then shut the valve off that is on the line going to the tank and open the little air vent on the side of the valve.  you should get water out of the hose.  if it is running out the air vent use an air compressor and give it a quick blast of air after removing the cap to the air vent.  careful not to over pressurise it.  just enough air so that it starts sucking air from it and the water drains from the boiler drain.  Hope this helps.
  • stevieg
    stevieg Member Posts: 19
    heating specialist of cape cod

    this may not be you rdomestic tank it could also be your xtrol tank it depends on a number of things, a series of steps need to be taken to find out . I will say if you turn off the cold water supply to the domestic tank maybe overnight and under normal working conditions,if the presure still goes up ,then chances are its not the tank,but the presure could alo backfeed through a mixing valve, say your kitchen sink fawcett and still presurise the tank there are so many posabilaties.
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