Low hot water pressure throughout house

Discussion in 'Plumbers' Talk' started by fooey, May 14, 2017.

  1. fooey

    fooey New Member

    Hi guys,

    Firstly let me say that I'm not a plumber but I'd really appreciate any help I can get here...

    We moved into to our place a year ago and at the time, we didn't have any issues with the hot water pressure/flow rate. Now though when trying to take a shower, the hot water comes out at a miserable rate. I've just measured it and we get something like 4.5 litres/min, cold water is not a problem (about 15 litres/min).

    I noticed something strange - just been away for 2 weeks and I'm pretty sure that the hot water pressure has dropped during this absence.... Could it be that not having hot water run throughout the system has let dirt/sediment settle somewhere? For additional information, we have a boiler on the ground floor and a hot water tank on the top floor.

    At a real loss as to take things further... any help much appreciated.
     
  2. nigel willson

    nigel willson Screwfix Select

    Possible air lock?
     
  3. terrymac

    terrymac Screwfix Select

    hi a few questions. are all hot water taps slow or just shower ? what type of shower is it, basic mixer ,thermostatic mixer ,electric ?
     
  4. nigel willson

    nigel willson Screwfix Select

    Just reread it, looks like the shower. Does it have filters in the inlets, check them!
     
    Chriscba likes this.
  5. fooey

    fooey New Member

    It's all water taps and not just the shower ....
    The shower is a basic mixer

    Thanks
     
  6. terrymac

    terrymac Screwfix Select

    before you went away did you turn off any stopcocks /valves ? take a look at the cold water storage tank ( in loft ?? ) make sure it is full of water and inside the tank ,low down ,are the water outlets ,make sure they are Clear not partially obstructed. this tank feeds the hot water cylinder.
     
  7. nigel willson

    nigel willson Screwfix Select

    Recon airlock. Triy connecting cold mains to hot for a short time , I usually do it with hot and cold washing machine taps in you have them. If that shifts it ,it was an airlock
     
  8. fooey

    fooey New Member

    I connected the hot water washing machine tap to the cold water one. Turned on both taps for a minute or so but that didn't have any effect - still low pressure.
    Just to add that I *think* that the pressure has dropped gradually over the last year or thereabouts...
     
  9. If it's been slowly getting worse over the past year or so, then I guess a build-up of gunge in a pipe is the most likely cause.

    You say the cold in the shower is delivering at around 15 lpm - is that fed from the cold tank in the loft or from the mains?

    Anyhoo, since the cold in your kitchen is (should be) from the mains, then your washing machine - assuming it's plumbed in near by - will also have a cold mains feed, in which case what you have tried by connecting the hot and cold W/M valves together should have worked to remove any air lock.

    It's unlikely to be a faulty shower since you say all hot taps are affected.

    So, that all leaves it more likely to be a partial pipe blockage.

    This will likely be either in the hot outlet from the top of your cylinder before it splits in to supplying the hot taps on both floors, or else - and actually more likely - it's in the cold feed to your hot cylinder.

    This enters the hot cylinder a couple of inches up from t'bottom and there should be a gate valve fitted there somewhere close to the inlet, with hopefully a drain cock there too. This pipe should be a 22mm size minimum (and most likely) and this should make its way upwards in as direct a line as possible to the cold tank in t'loft.

    First thing I think I'd do is to have a gander at the cold storage tank with a torch - is the water clean or is there sediment on the bottom at all?

    From reading posts on here over t'years, it would seem that the most likely place for this partial blockage (if that is what it is...) is where the cold supply elbows and enters the bottom of the hot cylinder, or perhaps even in the gate valve/stopcock that's fitted there.

    No easy way to do this, although it's well within the abilities of a competent DIYer; first shut off that valve to stop the hot cylinder being supplied. Connect a hose to the drain cock, open it and drain the hot cylinder completely... (best do this when you've all had baths and the tank is cold anyway...)

    Then undo that connection as it enters the cylinder and pull the pipe away - there should hopefully be enough play in this pipe to allow you to do this.

    Have a look in t'hole, and back in to the pipe end - what's it like?

    Get a bucket and open the gate valve - see how fast the cold rushes out - it should be pretty darned fast.

    If you've gone this far, I would personally replace that gate valve with a full-bore ball lever valve ( http://www.screwfix.com/p/pegler-ball-valve-red-22mm/45277 ) as they are more reliable and can be guaranteed to provide unrestricted flow. To do this you'll first need to drain that cold tank - shut off the cold mains supply to it, and open that gate valve to empty it (you could reconnect the pipe to the hot cylinder and then use the drain cock and hose as used before.

    If this pipe and valve is all clean and free from build-up and debris, then the only other possibility I can think of is the top cylinder outlet is partially blocked somehow. This certainly isn't impossible - there's been cases on here of debris likes bits of roofing felt and insulation falling in to the cold tank and making its way down to the cylinder, and then blocking the top outlet as it gets drain there by the outgoing hot flow.

    Any debris like this should be visible through that bottom hole when you remove that pipe - use a torch to help peer through.
     
    KIAB likes this.
  10. KIAB

    KIAB Super Member

    Seen pipes blocked solid by crud from the header tanks.

    A wet n dry vac is great tool for cleaning out the header tanks, after they been drained.
     
    retiredsparks likes this.
  11. fooey

    fooey New Member

    Hiya, thanks again for all your replies.

    I've been in the loft and there doesn't appear to be a cold water storage tank.
    I've attached a picture of the hot water tank and labelled pipes/taps. L is the inlet pipe.
    I believe I need to close the tap next to L.
    When I pull A, I can see water leaving the pipe and entering the opening at E, the same thing happens when I turn B. I guess that's one way of draining the cylinder.
    I'm going to do this now, undo the pipe entering the boiler at L and see what it looks like in there. Will report back.

    Do you know what F is ( you can see that there's some kind of dried spray of rusty? water on the wall beside it).
    And the opening at E seems to have a lot of build-up of stuff.
     

    Attached Files:

  12. terrymac

    terrymac Screwfix Select

    hi you have a pressurised cylinder and you should not go any further at this stage. all previous advice by all above posts do not apply ,all under the impression you had gravity fed.
     
    Deleted member 33931 likes this.
  13. fooey

    fooey New Member

    Thanks Terry. I have stopped what I was doing.

    Can you tell me how I can progress from here?

    Thanks.
     
  14. terrymac

    terrymac Screwfix Select

    fooey the system you have is fairly complicated and outside the scope of diy repair. my advice to you is to get a pro in . I can see from your pic ,that the pressure relief valve has been lifting and the tundish is covered in limescale and crud ( B And E ). there is a dark area just above the electric immersion heater ,which is a concern and needs looking at. F is an automatic air vent ,which allows air out of your central heating pipework . the way your megaflow works is :- mains cold water goes into it ,where it is heated by boiler or electric immersion heater, hot water comes out the top and is distributed to taps etc. various control gear protects from overheating and excessive pressure building up. these do not suffer from air locks . on the basis that the ingoing cold pressure determines the pressure coming out it appears you have a restriction , probably the pressure regulator , but not definitely .a full inspection on site can only establish that.regards terry.
     
    Last edited: May 28, 2017
  15. KIAB

    KIAB Super Member

    A unvented water cylinder should be serviced once each year, drained down, etc.
     
  16. fooey

    fooey New Member

    Oki doke, is this a something that a general plumber can do or do I need to find a more specialized plumber?

    Thanks again.
     
  17. terrymac

    terrymac Screwfix Select

    one who is qualified to work on unvented pressurised systems
     
  18. KIAB

    KIAB Super Member

    You have to G3 Unvented Qualification to work on the system.

    You need to make sure fitter is gas safe & has the Un-vented Certificate of Competence G3.
     
  19. Jeepers - I assumed it was a vented system... :rolleyes:
     
  20. terrymac

    terrymac Screwfix Select

    thanks for the like dev ad. I did ask early on in the thread to check loft tank as I was thinking along same lines as you ,but op gave no response and went down Nigel's air lock route. think you followed on. regards terry
     

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