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Reoccurring slow flow / airlock to cold tap

Discussion in 'Plumbing and Central Heating' started by wrightsonm, 21 Jul 2020.

  1. wrightsonm

    wrightsonm

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    Every few weeks at the moment I notice that the cold water flow upstairs is getting slower and slower until it stops.

    I have a CWT in the loft, 22mm feed comes out and down into the airing cupboard. There is a tee at about shoulder height with 15mm off the side that feeds into another gate valve and then shower pump.

    Just before the tee there is a gate valve which cannot fully close (maybe 10% water can still flow)

    The 22mm continues down to floor height then disappears into the bathroom to feed the bath, toilet and sink. Somewhere behind the tiling it reduces to 15mm to feed the sink. Dont know about the other items as it is all buried. The same 22mm feed from airing cupboard also serves the downstairs bathroom which is immediately beneath the upstairs bathroom. Dont know the size as it is all buried.

    Periodically when the flow gets slow I have found the easiest solution is to shut the gate valve just before the shower pump,disconnect the cold side of the shower pump (since it is a push fit) and then reopen the gate valve with a bucket nearby.

    I get a trickle then a cough and a splutter, then full flow. Reassemble and problem is solved for maybe 3 weeks.

    I have also tried the back feeding trick on the bath mixer tap by sealing it with my hand and opening the hot&cold. Ive had mixed results and found the shower pump pipe trick to be more effective.

    I don't want to be doing this operation every few weeks especially when those fittings arent really designed to be touched on a regular basis.

    Im looking for ideas on what the problem could be.

    Other things i know.
    Boiler is 30 years old. Newspapers under the floor next to empty flux pots where dated 1980s which dates most of the pipework in the house. Almost everything is copper 15/22mm. Shower pump was replaced by me 12 months ago and this problem surfaced about 3 months ago. I think the previous shower pump had been installed for about 10 years.

    CWT is always full so dont think the problem is the float valve. - do need to make a plywood lid to replace the polystyrene thing that is currently on top. Tank looks clean though there is plenty of limescale at the bottom (hard water area in Hertfordshire)

    Any ideas would be appreciated on this one. Looks like the 22mm gate valve does need to be replaced as it wont shut, but not sure that explains my problem. Also need to drain the tank to do it...

    Thanks
    Mark
     
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  3. JohnD

    JohnD

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    when you looked in the cold water tank, did you see any rust flakes? mortar drips? drowned pigeons? scraps of loft insulation?
     
  4. wrightsonm

    wrightsonm

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    It all looked clean in the tank. Only timescale sat at the bottom.
     
  5. oldbutnotdead

    oldbutnotdead

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    I wonder if your dodgy gate valve isn't opening fully or whether your new shower pump is sucking hard enough to get air in through one of the packing glands.
    Cold out of the tank- is it the usual side output or bottom? If side, is there a long stub before the drop?
    First job is swap that failed valve out. You'd be better putting a full bore ball valve in instead (i was shocked at the inner bore of a 22mm gate valve i took out recently, it was 15mm at most). Draining the tank is a 10 minute irritant
     
  6. dilalio

    dilalio

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    Pump feed should have it's own dedicated supply from the cwsc. That would sort this issue.
     
  7. Chris_W

    Chris_W

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    If only one tap is affected, I'd be checking this out first. Is it a screw down type? Yes - check out the washer and spindle. If no and lever type, then check for debris
     
  8. wrightsonm

    wrightsonm

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    There are 2 feeds from CWT, both come from the bottom of the tank. 1 for hot water cylinder, the other for the 2 bathrooms & shower pump.

    When it exits the CWT, it runs pretty flat before dropping down.
     
  9. wrightsonm

    wrightsonm

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    I could add a new feed to shower pump. But has been fine as it is for quite a while. Ive onky been in this house 18 months. It was fine for 6 months on the old pump before the pump sprung a leak, and then has been fine for 9 months on the new pump.

    I'm not saying you are wrong of course!
     
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  11. wrightsonm

    wrightsonm

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    2 sinks, 2 toilets, 1 bath are all affected.

    The shower pump also becomes intermittant (turns on and off) due to poor flow on cold side. I then detatch the cold side, run into a bucket, cough splutter and then everything is good again for a while...!
     
  12. oldbutnotdead

    oldbutnotdead

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    Mmm. Sounds as if you're getting air in the flat bit. Any scope to give it some angle?
     
  13. wrightsonm

    wrightsonm

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    I'll have to check in the loft. There is probably a bit of wiggle room to make it lower. Could be done at the same time as changing the iffy gate valve.

    I do wonder where the air is coming in from though...
     
  14. wrightsonm

    wrightsonm

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    I've checked in the loft. The is an extra gate valve that I'd forgotten about immediately next to the CWT before heading down into the airing cupboard. There is a slight downwards gradient. very slight, and no room to make it lower without notching the top of a joist.
     
  15. oldbutnotdead

    oldbutnotdead

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    Slight gradient is all you need. Is that valve wide open & working properly?
     
  16. wrightsonm

    wrightsonm

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    yeah that valve is fine. this one looks quite new too, still nice and shiny.
    Can't say i measured the gradient, but it has probably been that same gradient for the last 30 years or more...!
     
  17. oldbutnotdead

    oldbutnotdead

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    Aye. Job for the weekend is swap that dicky gate valve for a full bore ball valve (known fault, cheap fairly easy fix though you may need to trim the 22mm, ball valves are generally longer than gate valves). Run with that & see what happens, keep us posted :)
     
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