Shower is cold only

Discussion in 'Plumbers' Talk' started by Poppy 13, Jan 15, 2021.

  1. Poppy 13

    Poppy 13 New Member

    Shower runs extremely hot for about 15 seconds, then next to cold unless you lower shower head to floor and then marginally warmer for a few seconds. I have replaced the mechanical parts for the Mira 88 shower and that appears to work perfectly. I notice the hot water on leaving the top of the cylinder passes to both the bath and sink after passing the shower, and both sink and bath run hot perfectly. I also have discovered through getting very wet and cold that with the shower mechanical parts removed water pours happily out of the cold side, but only intermittently from the hot side. The hot exit pipe from the top of the cylinder that feeds the sink, bath and shower also has a T connection going up to a vent. The shower head is 2ft 6 inches above the sink taps and even higher above the bath taps. Is there a link here? Any advice welcome.
     
  2. Peterdevon

    Peterdevon Active Member

    How much above the shower head is the tank?
     
  3. Poppy 13

    Poppy 13 New Member

    Thank you for your very prompt reply. By the tank I assume you mean the smaller tank which is higher than the large cold water tank. Smaller tank is 7 to 8 feet higher than shower head right in the eves of the house. It couldn’t be higher! The system has worked well for 30 years since it was installed.
    What do you reckon?
     
  4. Joe the Plumber

    Joe the Plumber Screwfix Select

    Forget the small tank. That's for your central heating. It will be fed from the bigger one.

    There's clearly a blockage somewhere in the hot feed into the shower body. Is it a built-in valve or surface mounted?

    You'll need to determine if it's in the shower valve itself or the pipe leading to it. Much easier if it's surface mounted of course.
     
  5. Poppy 13

    Poppy 13 New Member

    Thank you Joe,
    The valve is surface mounted. I have taken the valve out and replaced it. From your reply the blockage has to be in the section of pipe that Ts off from the main pipe carrying hot water to sink and bath. How would you suggest I could clean this out? Unfortunately the shower feed pipe is behind the shower tiles etc.

    Going back to my original thought, do you think it might be a blockage in the vent pipe or maybe the water in the expansion tank might have got too deep and the end of the vent pipe might be under water?
     
  6. terrymac

    terrymac Screwfix Select

    Can you remove the entire shower body from the wall,to leave the open ended pipes exposed ? And then see what the flow from the hot pipe gives. You will obviously need isolators on hot and cold feeds to enable this.
     
  7. Poppy 13

    Poppy 13 New Member

    Hello Terry,
    Yes I should be able to do this, however I have already filled up the system leaving all pipe valves open having removed the shower valve itself. Water rushes out of cold side, but takes a long time for water to appear on hot side and lasts only a matter of 10 seconds, reappearing every 20 to 30 seconds. Very intermittent indeed.
    Regards, Richard.
     
  8. terrymac

    terrymac Screwfix Select

    If from an open ended pipe you do not get a constant flow, that could be an air lock . what type of isolation valve/s are on the hot branch pipe to the shower ?
     
  9. andy48

    andy48 Screwfix Select

    1. Could also be a sticky non-return valve or (partially) blocked filter.
    2. Photograph of shower might be useful.
     
  10. Poppy 13

    Poppy 13 New Member

    Hello Terry,
    There aren’t any valves at all between top of cylinder and shower head unless it is behind shower cubicle and would be inaccessible.
    Thanks,
    Richard.
     
  11. Poppy 13

    Poppy 13 New Member

    Hello Andy,
    Thank you for getting back to me. Unfortunately there aren’t any valves between the top of cylinder and shower assembly nor filters. Shower is immediately adjacent to cylinder. Please find photo below:
     

    Attached Files:

  12. andy48

    andy48 Screwfix Select

    1. Filters / non-return valves are often built into the shower unit, either where it connects to the pipework at the wall, or in the body of the shower valve.
    2. When you remove it from the wall, were there any signs of a piece of mesh / small plastic bobbin in the end of the hot pipe?
     
  13. terrymac

    terrymac Screwfix Select

    Have you actually removed the whole thing from the wall ,just leaving the two supply pipes only , nothing whatsoever attached to the pipes ?
     
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  14. Joe the Plumber

    Joe the Plumber Screwfix Select

    Mira 88s are really basic (a very good thing) and don't have restrictors or filters in my experience Andy, unless someone's fitted them as aftermarket items.

    As Terry says, the whole valve needs to come off the wall to flush the hot pipe through and also to check for debris in the valve inlet. It's only held on by the two pipe nuts and a little grub screw accessible under the bottom of the wall plate.

    Forget the expansion tank Richard. It's nothing to do with the shower.
     
  15. Poppy 13

    Poppy 13 New Member

    Thank you everyone. There is a very clear thought trail here that’s consistent amongst you all, so plan is to take whole shower unit off the wall, check for filters and debris, then blank off the cold outflow pipe and run the hot, with some brushing out with a narrow pipe brush. Hopefully it’ll clear. I’ll let you know how I get on.
    Richard.
     
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