Boiler pressure increasing no matter what

Discussion in 'Plumbers' Talk' started by rmurph17, Jan 18, 2020.

  1. rmurph17

    rmurph17 New Member

    Ok I’ll start from the top:

    1. Noticed my heating wasn’t coming on tonight when I got home from work,
    2. Went to boiler and noticed the low pressure light blinking and pressure gauge at 0,
    3. No big deal I say to myself, I’ll just refill the loop and bleed all the radiators,
    4. Turn the blue knob underneath that’s on the flexible pipe and let the gauge read 1.5 bar, turn off the blue knob again and turn on the boiler again,
    5. Sit and watch the boiler for a few seconds it gets up to 1.8 bar so I start working my way round all the radiators and bleed them till it’s just water one after each other from closest to boiler to the furthest,
    6. Go back to the boiler and it’s at 3 bar! So I immediately turned it off and went to the nearest radiator and undone the bleeder valve to let the system drain into a bucket and reduce pressure,
    7. Go back to the boiler and see the PRESSURE IS STILL RISING,
    8. I put buckets under every radiator in the house and keep bleeding for about 20 minutes but the pressure isn’t going down,
    9. My neighbour comes to my door to tell me there’s water spraying from my house,
    10. I go outside and see a 10mm pipe that was protruding from my wall with an stop end cap on it has burst in the wall of the pipe and it is spraying water everywhere,
    11. I go back inside and turn on every tap, eventually get enough flow that the pressure on boiler reads close to zero so I run out and use duct tape to close the burst pipe as best I can,
    12. I go back inside turn off all taps, close all radiators except the one closest but now the pressure is at 3.4 bar and is static.

    I have no clue what on earth is going on. The filler loop is closed at both vales: the blue handle on flexible pipe is closed position and I used a screwdriver to close the ball valve that’s underneath and is where the cold loop connects into the combi boiler.

    does anyone have any clue what is going on?
  2. Heat

    Heat Well-Known Member

    Hi, I would guess the filling loop was not actually fully turned back off.
    Very common for the valves on them to appear to be turning off, but are broken.
    The pipe to outside would normally be a 15mm pipe from the pressure relief valve on boiler. That valve is a safety valve and opens at 3 bar pressure. It works on a spring mechanism and closes off again (hopefully tight seal).
    If you do your water pressure to boiler and rad system again, then turn your mains off your property, you will find your boiler remains at your set pressure. (When heating is on it will rise slightly, but boiler expansion vessel will prevent it going too high, unless the vessel is faulty)
    rmurph17 likes this.
  3. Heat

    Heat Well-Known Member

    The fact you mentioned the pressure continued to rise after the boiler was switched off definitely suggests the filling loop is faulty
    rmurph17 likes this.
  4. rmurph17

    rmurph17 New Member

    I thought that but I’ve fully tightened both valves on the cold filling loop is it possible both valves have failed?

    I have walked the perimeter of my building and cannot find an external pressure release valve.

    The pipe coming out the front of the property is a 10mm plastic pipe with end stop on it (picture attached).

    I’ve cut the pipe pictured and it started gushing water out, 15 mins later it is still gushing water and despite the initial drop of pressure on the combi boiler gauge going to 1.0 bar it has now settled at 1.9 bar and doesn’t seem to be moving, but the house is now gushing water out the front pipe.

    I tried to turn off the mains water supply to the house but the stopcock is seized tighter than two coats of paint.

    I’m going to cut the outside pipe as close to the rupture as possible (it’s unfortunately extremely close to the wall in picture under that tape) then force in a 10mm to 10mm push fit coupler then add a short length of 10mm pipe then stop end cap it and put a flue cage around it so it’s protected from future damage.

    Apart from both valves in the cold feed being broken what else could be wrong?

    Attached Files:

  5. Muzungu

    Muzungu Active Member

    Disconnect the filling loop, at least you will then know that it is not that.
    rmurph17 likes this.
  6. rmurph17

    rmurph17 New Member

    Apologies, I’m not a plumber so my knowledge is very limited. How do I disconnect the loop?

    For anyone else reading the combi-boiler is a Modena 80E, I forgot to mention it earlier.
  7. Heat

    Heat Well-Known Member

    A pipe coming from a boilers pressure relief valve would be 15mm and copper.
    Filling loop best disconnected to test as Muzungu said
    rmurph17 and Muzungu like this.
  8. Muzungu

    Muzungu Active Member

    Filling loop should be a flexible braided pipe with hand turnable connectors each end (probably). Just disconnect the boiler end and make sure you have the valves off first!
    rmurph17 likes this.
  9. Mike83

    Mike83 Well-Known Member

    There’s a chance that 10mm pipe is the prv discharge pipe.
    Is the boiler close to this pipe?
    If you post picture of the boiler it will help.
    rmurph17 likes this.
  10. rmurph17

    rmurph17 New Member

    Here is the pictures of the boiler, you will see I have no access to the other end of the braided hose. The blue valve at the top end of the braided hose is what I turned clockwise to fill the boiler.

    If it is turned clockwise, the pressure increases rapidly. If it is in the 12 o’clock position I cannot turn it any further anti-clockwise and the pressure remains static (or slightly increasing).

    If you follow the pipe across the T and elbow towards the inlet into the combi-boiler there is a ball valve that used to have a handle, the handle was broke before I moved in. Initially I did not touch this valve but when pressure skyrocketed I used a screwdriver to turn and close it.

    In this state the pressure will slowly rise unless I let water out by a radiator bleeding port. However that only stops the rising pressure.

    This all happens while the combi boiler is completely off. 0BF48176-1C08-4C8F-B38C-344C95BF25F1.jpeg E35FFF41-1662-431C-A66F-9D2ABA97E9C5.jpeg 4DB7D851-8805-4ABC-9FC8-1E2739FA62E0.jpeg 1B656B5A-404E-464F-AEE4-1CE0F72652A8.jpeg DFD94C34-B451-45FA-81C2-F1B6BE362B2A.jpeg B0A60F67-4CB3-4D7B-B35C-73DBA9BDFF4B.jpeg 4F9DCC53-2485-4E8E-9981-D84AD74A9AEE.jpeg
  11. rmurph17

    rmurph17 New Member

    It is at the opposite end of the house near the front door while the combi boiler is at the rear beside the kitchen back door.

    The only pipes coming out the wall at the boiler (I even checked inside the hedge incase it was hiding others) are as per the picture below

    Attached Files:

  12. rmurph17

    rmurph17 New Member

    Well I think renewing the pipe that went outside has fixed the issue.

    I did what I said in previous post (not fit the cage yet) after turning on then off the two blue taps, then refilled the system, re-bled the radiators and it’s holding at 1.0 bar. I’ve overridden the timer so it will heat now and it’s still warming up to temperature so I’m hoping that this saga is solved now with any luck.

    If it does I will be amazing at the oil boiler having survived 3.6-3.8 bar for a few hours
    Muzungu likes this.

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