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Can't pressurise boiler

  • 07-03-2018 10:46am
    #1
    mloc123
    Registered Users, Registered Users 2 Posts: 9,454 ✭✭✭


    Recently moved house and now have a Prima F gas boiler (must be 20yrs old?) which is on a sealed system. The pressure is at 0.7 at the moment and I am attempting to get that back to 1.

    I have found the filling loop which is in our hot press, it is fed from the tank in the attic. I opened the valve and left it open for 20mins or so but the pressure has not increased at all on the gauge (which is in the kitchen at the boiler).

    Am I missing anything here?


Comments

  • #2
    wiz569
    Registered Users, Registered Users 2 Posts: 1,709 ✭✭✭wiz569


    If its fed from the tank in the attic then that's probably the most, pressure wise, you will get.

    The boiler should still fire at that,well at least my glow worm boiler does,which is a semi-sealed system like your own.


  • #3
    crosstownk
    Registered Users, Registered Users 2 Posts: 12,863 ✭✭✭✭crosstownk


    By any chance are you subject to the current water pressure reductions/restrictions? If so, your pressure may not be enough.
    Untitled Image




  • #4
    mloc123
    Registered Users, Registered Users 2 Posts: 9,454 ✭✭✭mloc123


    crosstownk wrote: »
    By any chance are you subject to the current water pressure reductions/restrictions? If so, your pressure may not be enough.

    Thought of that and had a look up in the attic to make sure the tank is full, it is.

    Boiler fires okay and all rads are hot.. so no real issue I guess. Plumber is out in 2 weeks to service it so I will mention it to him also. Pressure gets up to 1.5 bar when the heating is on.

    It looks like 10m head = 1bar, so it seems unlikely that the system could every get up to 1bar gravity fed in a 2 story house.


  • #5
    K.Flyer
    Registered Users, Registered Users 2 Posts: 8,565 ✭✭✭K.Flyer


    mloc123 wrote: »
    Thought of that and had a look up in the attic to make sure the tank is full, it is.

    Boiler fires okay and all rads are hot.. so no real issue I guess. Plumber is out in 2 weeks to service it so I will mention it to him also. Pressure gets up to 1.5 bar when the heating is on.

    It looks like 10m head = 1bar, so it seems unlikely that the system could every get up to 1bar gravity fed in a 2 story house.

    Water pressure will equate to 0.1 bar of pressure for every metre of head from the tank to the gauge. Given most boilers are on the wall downstairs you may only have 6 - 7 metres of head (0.7 on the gauge)
    The reason for the big jump in pressure indicates that the expansion vessel needs attention. It is either undersized or the air pre charge pressure is incorrect or it needs replacing.


  • #6
    mloc123
    Registered Users, Registered Users 2 Posts: 9,454 ✭✭✭mloc123


    K.Flyer wrote: »
    Water pressure will equate to 0.1 bar of pressure for every metre of head from the tank to the gauge. Given most boilers are on the wall downstairs you may only have 6 - 7 metres of head (0.7 on the gauge)
    The reason for the big jump in pressure indicates that the expansion vessel needs attention. It is either undersized or the air pre charge pressure is incorrect or it needs replacing.

    The pressure should not jump when the boiler is on... Or should not jump so much?


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  • #7
    K.Flyer
    Registered Users, Registered Users 2 Posts: 8,565 ✭✭✭K.Flyer


    mloc123 wrote: »
    The pressure should not jump when the boiler is on... Or should not jump so much?

    If there is no room for expansion due to a faulty expansion vessel then off course it will go up. Heat creates expansion, expansion in a sealed system increases pressure, its simple physics really.


  • #8
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    mloc123 wrote: »
    Recently moved house and now have a Prima F gas boiler (must be 20yrs old?) which is on a sealed system. The pressure is at 0.7 at the moment and I am attempting to get that back to 1.

    I have found the filling loop which is in our hot press, it is fed from the tank in the attic. I opened the valve and left it open for 20mins or so but the pressure has not increased at all on the gauge (which is in the kitchen at the boiler).

    Am I missing anything here?

    To get 1 bar from a head of water such as an attic tank, requires 10 meters from measured point to the water head. Each meter = 0.1 bar.

    So an attic tank might give 0.5 to 0.6 bar or so.


  • #9
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    mloc123 wrote: »
    The pressure should not jump when the boiler is on... Or should not jump so much?

    It should go up a little in the sealed system.


  • #10
    K.Flyer
    Registered Users, Registered Users 2 Posts: 8,565 ✭✭✭K.Flyer


    Bruthal wrote: »
    It should go up a little in the sealed system.

    It can go up quite a bit on a sealed system if there is absolutely no air in the expansion vessel.


  • #11
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    K.Flyer wrote: »
    It can go up quite a bit on a sealed system if there is absolutely no air in the expansion vessel.

    Yes I was assuming a properly working expansion vessel. If there is a water filled expansion vessel and no air anywhere in the system then it will be quickly up to the pressure release level I would think.


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