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HELP! Old Boiler assist needed!


There is a 1950's Kohler 22" Oil boiler which was converted to gas in my mother-in-laws basement.

The pressure in the boiler is rising extremely high every time the boiler fires.

The only way I have been able to reduce the pressure at all is by manually using the lever on the top of the pressure relief valve.

I did find the water feed valve open (that is loosened) and the bar pointing straight up. I am assuming this allowed a lot of water to build up in the boiler?

The pressure entered the danger red zone last night so I shut the whole system down a released some pressure manually.

What are some of the common causes of this pressure and is there anyway I can fix it?

Do I need a new pressure valve?

Is the boiler too full with water?

What position should the feed valve be in?

ANY help is greatly appreciated!

Thank you!

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  • Jamie Hall
    Jamie Hall Member Posts: 22,947

    I presume this is a hot water system?  And not steam?  In either case, turn the system off and do NOT attempt to use it again until you find out why the pressure relief valve -- which is your last line of defence against a very loud noise -- is opening.

    You could have a leaking feed valve.  If so, it should be replaced.

    The expansion tank could be completely waterlogged.  If so, you could try to restore it to life.  If it is the bladder type, there is a Schrader valve on it with which you can restore the air charge -- unless the bladder is shot -- without having to drain the system (you will have to drain enough water to relieve some of the pressure, though).  If it is the older type tank without a bladder, again there may be a valve on it to allow you to add air; the older tanks should be more or less half full of air and half full of water at operating pressure.

    Hard to say if you will need a new pressure relief valve.  If it reseats OK, probably not.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • evergreen1985
    evergreen1985 Member Posts: 5
    More info

    Thanks Jamie,

    Yes, it is a water system.

    Let me be clear, I cannot tell if the pressure valve was working on its own.

    I had to MANUALLY lever the pressure down with the valve.

    My guess was there was something wrong with the valve.

    Would too much water in the boiler cause this pressure issue?

    Thanks in advance.
    STEVE PAUL_3 Member Posts: 126
    Relief valve opening

    On a water boiler is due to over pressure. It sounds like you have a combination pressure reducing valve - pressure relief valve. The pressure relief valve part is factory set at 30PSI. You also may have a water logged expansion tank. I would suggest replacing the combination valve with separate pressure and regulating valves. Combination valves in my location are no longer permitted. I would also re-charge or replace the expansion tank.
  • evergreen1985
    evergreen1985 Member Posts: 5
    So I drained the Expansion Tank...

    And even with the system OFF the pressure was WAY up this morning.

    I am nervous about it.

    What else should I be looking for?

    I have attached some photos for some perspective.

    Thanks in advance.
  • billtwocase
    billtwocase Member Posts: 2,385
    how much

    water did you get out of the tank? This is why I use 5 gallon buckets. If you got a gallon or two and it stopped, it is most likely still full. You need to get air in the tank for it to drain fully. 
  • evergreen1985
    evergreen1985 Member Posts: 5
    I probably....

    Took out 3-4 Gallons.

    Should I do more?
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    A few things

    That tank needs to be emptied all the way. 25 to 35 gallons is typical.

    Also I hope you have a secondary relief valve on the boiler, b/c the one next to the feed valve will not cut it.

    All that is a an over pressure bleed, Not rated for any real btu capacity, and not ASME rated.

    You are right to be cautious and concerned.

    I would advise having a boiler pro give the system a once over.
  • evergreen1985
    evergreen1985 Member Posts: 5
    That is what I thought....

    That is the ONLY pressure relief valve - and that was what worried me.

    I guess I will have to have someone come out and look at it for sure.

    I am in the process if draining it all now.

    Is there anything else I should do in terms of checking?
  • billtwocase
    billtwocase Member Posts: 2,385

    the tank totally, and start it from scratch. Some areas may frown upon using a new inline valve, should that one be no good. I have never seen an inline relief valve fail to open if needed. One on the boiler would be nice, but that one will work, unless there is a shut-off valve between that and the boiler. They were used years ago for reasons. Old boilers didn't have all tappings available like the new ones do. I would also suggest you have someone come out and look it over 
  • Matthew Grallert
    Matthew Grallert Member Posts: 109

    I would also check the accuracy of the gauge on the boiler.  By putting another gauge on a boiler drain somewhere you can verify the actual pressure in the system. 


    STEVE PAUL_3 Member Posts: 126
    Long distance diagnosis

    Is not always easy. Based upon your pictures and your description, the pressure is going up from one or more of the following reasons.

    1- The pressure regulating valve is not set or operating properly and should be replaced.

    2-The expansion tank is water logged and should be drained. To drain it, shut the valve from the system, open the drain valve, open the tank vent valve to admit air into the tank, drain tank until ALL water is drained. Reverse the drain-down procedure.

    3-The pressure relief valve is weak or has dirt not allowing it function as a true SAFETY devise. Replace it with a new 30PSI relief valve, not a combination valve.

    4- If the boiler is used to make domestic hot water, there may be a leak in the coil that is raising the boiler pressure. Replace the coil, or bite the bullet and replace the boiler.


  • JohnHenry_2
    JohnHenry_2 Member Posts: 70
    Pressure regulating valve

    If the pressure goes up overnight with the system off, it would seem that either the pressure regulating valve is faulty or someone is sneaking into the house and pumping up the system while everyone is sleeping... Does the pressure in the heating system ever get up to the pressure of your potable water supply?

    It's probably time to have a real boiler pro come in and assess the system and fix it. To bring it up to modern safety specs he'll need to at least replace the pressure reducing valve, add an ASME rated pressure relief valve rated for at least the heating capacity of your boiler and add an anti-back flow valve to insure your heating system water doesn't contaminate your potable water.

    It won't be free but it will be worth every penny if properly done.
    The bitterness of poor quality remains long after the sweetness of low price is forgotten.
  • icesailor
    icesailor Member Posts: 7,265
    Combo. Pressure Reducing Valves-Pressure relief Valves:

    This is probably another one of my incorrect assumptions but,

    Massachusetts was the leader in Temperature and Pressure Relief valve requirements because of exploding Brown Brothers Copper hot water storage tanks and "side arm" gas water heaters. Hence, gas controls and the relief valves. Hence, Watts Regulator Company. PRV/PRV's were conveniently installed so that they would drip into a sink if they leaked. The water heater may be 30' away, but by goodness, if they opened, they would leak into the sink. Of course, if the water in the tank was over 360 degrees ( the temperature that 50/50 solder melts), the tank would come apart and the now bomb would usually go through the roof, never to be seen again. Or, if the Pressure Relief opened, and caused the pressure to drop below the boiling point, the water immediately turned to steam. If you ever go into a building with a waater heater biyncing around the floor, DO NOT OPEN THE FAUCET. Shut off the energy source from somewhere else and LEAVE THE BUILDING!!  Cooler heads prevailed and we have Chapter 142 of the General Laws. Which in part state that the PRV/PRV MUST be located in the top third (1/3) of the tank, in the hottest water in the tank. Therefore, if the pressure (which is specified) exceeds the set point or the temperature exceeds 210 degrees, the valve will open and let HOT water out. This hot water is replaced by cold water. And here is the rub. Said cold water will flow into the overheated heater faster than the BTU input of the heater can recover the the hot water lost. It is the cold water that is the safety factor and has a BTU cooling factor.

    Hence,I've not seen any Pressure Relief Valves mounted on the bottom of boilers. A water heater full of non-potable water. And it was my understanding that the function of the pressure reducing valve was to provide cold or cool water to the boiler to cool it down faster than the burner can heat it. If the relief valve leaks, it gets replaced by cooler water.

    Then, we get to those combination units that are illegal in Massachusetts (or so I was told) because, if the relief valve is leaking, the cold water, while trying to get to the boiler, just leaks out the relief valve and never gets to the boiler. And they are very expensive because first, the Pressure reducing Valve is 1/2" and so is the Pressure Relief Valve. While a normal Watts 374A is 3/4".

    Replace the whole mess and make it right.

    Or so it seems to me.
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