Strange pressure on bathroom basin

Discussion in 'Plumbers' Talk' started by Steve698, Jul 11, 2019.

  1. Steve698

    Steve698 Member

    Last couple of days our bathroom hot tap has been misbehaving. When turned on the hot tap emits water under normal pressure but once it's been running for 10/15 secs the pressure gradually drops to about half of what is normal. I thought it may be a problem with the cartridge so I switched the hot and cold and nothing changed, the cold is fine but the hot not. We are on a gravity fed system and all other hot taps in the property are running normally. The water is still really hot but this fluctuating pressure is a bit weird - any ideas ?
  2. Joe the Plumber

    Joe the Plumber Active Member

    Possibly something is expanding once the water gets hot and cutting the flow rate down, but I couldn't guess at what.
  3. Heat

    Heat Well-Known Member

    Only things I can think of is the rubber tap washer (if standard works) is expanding and water is being closed down due to the works being faulty - only part opening.
    Or you have a flexi hose to taps and it is collapsing.
    Or debris in a filter or valve supplying tap
  4. Steve698

    Steve698 Member

    No tap washers as it is ceramic cartridges.
    Flexi hose is possible.
    Debris also possible.

    What about some kind of air lock ?
  5. terrymac

    terrymac Well-Known Member

    Check the condition of the cold water storage tank in the loft. Particularly for any signs of debris / loft insulation etc having got into the tank. There is possibly a partial blockage on the branch pipe to the basin . If you have isolators on hot and cold to basin ,You could undo the flexi hose to tap and direct it into a bucket and establish if the flow is OK when not connected to the tap.
    Is the cold supply from mains ,or loft tank ?
  6. Steve698

    Steve698 Member

    Cold supply is from loft tank.
    The tank was completely cleaned out 18 months ago when I fitted a new bathroom, it is spotless and well covered.
    I do have isolators on both hot and cold, looks like I may be taking a few things apart, doh. I'm hoping it's a flexi hose problem if it's in the pipework it will be a pain to deal with.
  7. terrymac

    terrymac Well-Known Member

    Easy way to establish if its the hose ,just swap them over. If the cold then runs slowly and the hot OK its the hose!! If hoses run fine into a bucket ,its the tap.
  8. WillyEckerslike

    WillyEckerslike Well-Known Member

    I've come across a situation where a piece of debris in the cylinder was rising with the discharge of hot water and restricting the outlet only to drop down again when the flow stopped. There's been at least one other incident on here of a similar nature. If it was that though, other taps would be affected you would think.
  9. DIYperson

    DIYperson Member

    Willy, I had the situation you described when the sacrificial anode in the hot water cylinder disintegrated and its rubber washers (like rubber penny washers) floated up and across the cylinder outlet, restricting the flow after a few seconds. I noticed the effect more on the bath hot tap than the basin or kitchen sink hot taps but that was probably to do with the pipe diameter supplying the taps.
    WillyEckerslike likes this.

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