New shower leaking when boiler fires up

Discussion in 'Plumbers' Talk' started by Useless 1, Jul 27, 2018.

  1. Useless 1

    Useless 1 Member

    Evening all. I've just installed a bathroom and the shower has just leaked when the boiler fired up for hot water. It stoped leaking when the call for heat switched off. It's a megaflow stored hot water system.

    I'm unsure as to why this might be. The shower and all other bathroom plumbing was unchanged as it was all like for like identical swaps right down to the same brand and model shower.

    What did change was the client had to up the pressure on the heating system as it fell below operating parameters due to the towel rad coming off (and the flipping trv constantly dripping whilst it was off for those 6 days)

    I'm thinking my first port of call is ease back the pressure on the heating system and seeing if helps. Is there anything else I could try that I don't know about?
     
  2. Allsorts

    Allsorts Super Member

    Is the expansion vessel pressurised correctly? What does the system pressure do as the boiler heats up - it should remain reasonably constant?

    If it soars, then the EV is suspect. Likely either discharged or punctured.
     
  3. Useless 1

    Useless 1 Member

    Thank you Allsorts. I'll investigate the EV and see what I can see.
     
  4. Allsorts

    Allsorts Super Member

    What type of pressure gauge do you have? What does it read 'cold', and what happens as the boiler gets to working temp?

    You have a Megaflo type system? In which case there will be at least two pressure gauges - one on the boiler to indicate the 'system' pressure and an other on the hot tank indicating 'stored hot water' pressure. I suspect the latter will be reading high when it's being heated.

    Both the boiler 'system' and the hot cylinder have expansion vessels.


    Can you clarify - what exactly is leaking? Water out of the shower head?
     
  5. Useless 1

    Useless 1 Member

    It is the shower head itself that is leaking when the call for heat is made. A good steady run of water. Not enough to produce a jet but enough to make a decent splash when it hits the shower tray.

    I'm heading back to check the pressure gauges around the system today. I'll initiate a call for heat and see if the same happens again. If the waters hot I guess I know the issue is with the megaflow pressure. Odd though since I thought heating the water in the cylinder was done by a closed loop. The same water recirculates, heating the water in storage doesn't it? How would that push water out of the hot water cylinder under enough pressure to force it out out of the shower when its valve is set to closed?

    You'll have to excuse me. I'm a lowly general builder, not a plumber. Well, not beyond straightforward pipe replacement for kitchen and bathroom installs.
     
  6. Useless 1

    Useless 1 Member

    Allsorts - I'll get back to you on the pressure gauge readings on cold and when warm.
     
  7. Allsorts

    Allsorts Super Member

    Yes, there are two 'systems' which are separate from eachother.

    The first - the boiler 'system' - holds a sealed amount of water which is circulated around the boiler, the heating coil in the hot tank and the radiators. This is pressurised to around 1.2bar (can vary a lot, but ideally shouldn't climb much above 2 bar when hot).

    The second is also pressurised - by the water mains - but is the water that's stored in the hot tanks and comes out your hot tap when opened. This is usually held at 3 bar pressure to give a good gush...

    As water is heated up, it expands. Since both these systems are effectively 'sealed', if the expanded water wasn't allowed to go somewhere the pressure would soar dangerously (but would ultimately be discharged safely out a copper pipe to the outside of your house when it hits 3 bar - so don't worry...).

    Ok, where that expanded water goes is to an expansion vessel - or two in your case, one for each system. These vessels have an expandable space inside them, so the idea it they can take whatever water is needed so that the system pressure actually remains pretty constant; when the system cools back down, the water in the vessel can return.

    If the vessel is faulty (or needs recharging) then the water cannot find anywhere to go so the system pressure goes up dramatically - this will be obvious from the pressure gauge readings.

    The boiler system gauge should ideally be sitting at around 1.2bar, and the hot tank store one at probably 3 bar.

    I suspect that the hot store pressure is climbing more than you want and this is forcing water past the shower valve. Mind you, it's every bit as likely that the pressure is only going up a perfectly normal amount, but your shower valve is worn :)
     
  8. Useless 1

    Useless 1 Member

    Pretty sure it's not the shower valve. It's a brand new shower!

    Didn't get the chance to get over there today to check the system pressures so tomorrow it is. Thank you for your detailed thoughts on the matter. Fingers crossed they solve the conundrum for me.
     
  9. Allsorts

    Allsorts Super Member

    If you could post photos (reduce them to below 2MP in size) of the Megaflo and also showing the pressure gauge, and ideally also one of the boiler and ditto, that might help folk on here.
     
  10. Useless 1

    Useless 1 Member

    Got to the bottom of it.

    It was the internal EV inside the mega flow. It needed recharging. It must’ve looked like a shrivelled teabag before I got to work on it. It took almost 35 minutes to repressurise. No more wailing banshee pipework and no more water being forced through the shower head.

    Allsorts - your advice was really useful and put me on the right path to the fix. The clients were really happy to get it resolved without further cost to them and I secured another bathroom refurb off the back of my willingness to sort out the issue without hesitation. If I could buy you a beer I would sir. I can’t so a heartfelt thanks will have to suffice
     

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