W. Bosch 37 CDi combi - overheat & PRV dump.

Discussion in 'Plumbers' Talk' started by Peter D. Alderson, May 2, 2016.

  1. Peter D. Alderson

    Peter D. Alderson New Member

    Devil's Advocate - I have picked up on your help to 'jsaipe' Dec 7 2013 & been hugely helped by your clear instruction on EV checks - those & more.

    Over the holiday I pressed BOOST, done many times before. This time temperature & pressure ran away at alarming rate - with water dump via PRV. Hastily cut Elect Power to shut down..

    Since then: checks round system. Water overflow: no problem, pressure stays '0' & all water vents.
    Condensation drain: all clear; deposit removed from trap (teaspoon full). Repressured EV with footpump to 1.25 bar & pressure held steady all day. (No water from schrader valve). BUNGED OVERFLOW with cork & jubilee clip & opened mains inlet valve. Pressure held, no leakage. Turned heating control to min (pipe circuit still open). Turned hot water control to low. Turned on Elect. Power & pushed power switch. System started normally and temp. ran up. At 44 deg C. pushed for power off & shut down system.
    Result: Warm water at nearby tap.

    QUESTION: Can you give your clear instructions for re-setting the PRV please?
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    Why on gods earth would you bung the pressure relief outlet? It is a safety device designed to relieve the pressure is as your boiler is doing over pressurising. You ran the risk of at best a ruptured gasket, at worst a big bang and no more boiler.
    The PRV is a self restting device so no instructions needed, your boiler has all the sysmptoms of a failed Thermistor.
    Get in a gas safe fitter who can check it through for you
     
  3. Hi Peter.

    As Dave says - remove that bung...

    I don't fully understand your post above. It sounds as tho' you've resolved the problem by recharging the EV (can I ask what pressure the air side was at before you started pumping it?)

    What does "System started normally and temp. ran up. At 44 deg C. pushed for power off & shut down system.
    Result: Warm water at nearby tap.
    " actually mean? You ran the boiler until it reached 44oC and then you turned it off? Why?

    And it's only delivering warm warm water - not hot as before - at your hot tap?

    What is the system pressure doing during all this?


    Anyhoo, back to your main question - the press relief valve. Are you saying that water now trickles out your discharge pipe? If so, that is very common - it sits there 'seated' for years, so finds it hard to re-seat in the exact same place after it's been opened (imagine the imprint yer arris makes in a cushion after a couple of hours... You then get up and sit back down - what are the chances of yer cheeks landing in exactly the same place...?)

    Often they need replacing - but this is really a plumber's job. It ain't hard, but not one I relish myself either (poor access, seized nuts etc...). You can try opening it again manually and then letting it 'slam' shut a few times and see if that does the trick. Can you post a photo of your valve?

    Er, do this after you've removed yer bung...
     
  4. Peter D. Alderson

    Peter D. Alderson New Member

    Hi to Dave does Gas and to Devil’s Advocate,

    Thanks for your replies. First of all yes, I am aware of the danger of bunging up the overflow – hence the caution about restarting the system at a very low level and
    stopping at 44 deg C & turning off again.

    Also I have made a request for a specialist to come and give the system a going over.
    To get the ball rolling over the holiday and to try to work out what had happened I
    took things as far as I did.

    At first I didn’t realise the Diverter Valve and the Pressure Relief Valve were two
    separate items. One or other of these two has remained open so that all water
    into the system by way of the inlet valve vents straight out of the overflow pipe.
    Hence the cork. I see the Diverter Valve making/attempting a change when
    Reset is pressed. However, remove cork, water rushes out, pressure to zero and water continues to flow from the overflow.

    Before re-pressurising the EV the reading at the schrader was zero. Since re-pressurising it has remained steady at 1.25 bar for over 24 hrs (even with a slow drip from the bung). I would rather leave accessing the PRV to the technician as access is poor & I was only experimenting to see how bad the problem was. The boiler needs a service and I was planning to get in spares so that down time can be as short as possible.

    I’m still not 100% shure if the Diverter Valve and PRV are both not re-seating together, or only one of them. (I see a new PRV is not that expensive but the Diverter complete with motor is).

    As a side issue – I have ordered a new Charging Link Key as mine broke a couple of years ago and I now realise the lack of turning off the mains at this point has probably been the cause of slow losses of pressure in the past. I also hadn’t realised the significance of keeping below 3 bar and on occasion it has gone over.

    So, thanks again – at least we can limp along untit qualified help is at hand.
     
  5. The diverter valve has nothing to do with your leak. It's all down to the PRV.

    It sounds pretty stuck open! What type of 'knob/lever' does it have on it? There is no harm in trying to reseat it - all you'll be doing is opening it up again, and letting it 'snap' shut.

    The loss of water out the discharge pipe shouldn't really affect the air pressure side of the EV, so it's good that it's staying where you pumped it to.
     
  6. Peter D. Alderson

    Peter D. Alderson New Member

    That's grand, thanks very much. You've zeroed in to the nub & now have the confidence to set all to rights & get something from the system before the technician comes & gives it the once over and his seal of approval.

    The PRV became visible after shifting a wall cupboard beside the heater (pix attached: sorry had to reduce it to GIF to get it in). Presumably the red handle is where to reset the valve - very cramped position? [N.B. the small box btm right of the frame is a supplementary heater control box for the Passive Energy Heating control, attached to the white cable in the front of the frame].

    PixPRValveHtr16.gif
     
  7. Quite possibly the worst quality photo I've seen on here... :p

    I use this: http://jpeg-optimizer.com But actually, the simplest method is to set yer camera to, ooh, 3MP resolution, and the photos will almost certainly come out <2MP



    Anyhoo, does it look like this: s-l1000.jpg

    If so, try flicking that lever right down repeatedly, allowing it to 'snap' back into position each time.

    If that doesn't work, then it's possible it can be opened and cleaned in case there's a bit of grit in there, but most plumbers will - quite rightly - chust replace it.
     

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