New walk in shower won't drain ? Getting airlocked?

New professionally installed walk in shower. After being left unused for a period on running the shower the shower tray fills up with scummy bubbly water and gets practically to the point of escaping over the ledge where you walk in. At that point we chicken out and pull out the big chrome insert that covers the shower drain, and all the water dissappears in a trice. Putting the chrome cover back in/on and the water thereafter flows away freely untill the shower has been stopped for a period (an hour or two?).
I can't find the exact shower waste fitting on the web but it's a shallow chriomium plated plastic dome about 5" across with what looks like a 3 sausage-segment air vent holes in the top, about 2cms P.C.D., waste shower water is intended to drain away under & around it's perimeter. 'Cept it doesn't without that bit of persuasion. It seems it might be at least similar to something called a "Fastflow" waste.
The walk in shower replaced the existing standard bath, but the waste is perversely at the walk in end and the pipe had to be extended I'd say the run to the soil stack is a bit over 3 metres and the fall is less than the depth of the joists with one right angle bend. However with the domed chrome insert removed it drains OK. If anything has to be changed under the floor it can't be done, it's all sealed up :-(
I wasn't aware that these shower wastes were such a complicated affair with concentric cups and sleaves. Exactly what it is all supposed to do defeats me. Anybody come across anything like this before P.S.E. ?
DG
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On Tue, 30 Aug 2005 19:33:49 +0100, Derek ^

I suspect that the fall on the waste pipe is inadequate for the length and diameter, given the waste fitting.
I remember reading somewhere (but can't find the reference now) that some types of "mushroom" shower drain can capture a bubble of air but that this goes through to the drain if the flow is fast enough. Otherwise, the bubble causes the flow to remain restricted. Lifting off the cap effectively removes this and allows full flow through the trap.
The only two components that can be involved are the waste fitting and the pipe, but as you say, they are sealed down.
Did the installer do the whole job? If so, or anyway, I would get him back to fix it. If it does involve ripping the lot up, then I would expect him to take the cost. He should have done the job properly in the first place.
--

.andy

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wrote:

Spoken to the fitter, he tells me there is a HepVo valve under the floor close to the shower. Given that the fall is not great I'm wondering if the "head", which may only be 4-5 cms, is enough to open the valve fully until there's a surge caused by lifting the chrome dome. If left to it's own devices with the shower shut off the water does run away eventuallty.
I'm homing in on this as an explanation.
On the HepVo website the examples all illustrate a substantial head , even with a horizontal installation.
http://www.hepworthplumbing.co.uk/hepv2.htm
Unfortunately I can't seem to open their PDF design guide. :(
Do these things have a correct and incorrect orientation the fitter could have got wrong? I've never seen/handled one myself..

Yes. 18 years in the bathroom business.

Absolutely. SWMBO *doesn't like* paddling in a whole load of scummy water when she's showering. :((

DG
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On Wed, 31 Aug 2005 13:13:33 +0100, Derek ^

It was OK for me, but most of it is on the web pages anyway by clicking through the tabs. They make one version intended for horizontal use that has a fitment to go straight onto the waste fitting, and is then angled at 87.5 degrees (normal slope).

Yes they do. If he had it the wrong way round it wouldn't work at all in normal use but will eventually open at 500mm head. If the trap weren't working properly, you wouldn't be able to get correct results by removing the cap of the waste.

Then he ought to know what works I would have thought. Is it the first time he has fitted this waste type I wonder.....

--

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    We have a similar experience. As Andy has said it seems to be related to the design of the drain and apart from regularly dehairing it, there seems to be no satisfactory answer. I've considered drilling a hole in the top to see what this does, but I too would like to understand it. In our case, the run to the main drain is <1M of 40mm pipe, so it's not the drain blocking. The problem does seem to come and go, but keeping the trap clear does help.
    Regards     Capitol
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Capitol wrote:

The chrome thing in my one has a screw height adjustment on its underside. Hence you can tweak the height above the surrounding tray. I found my one need raising a mm or two to get suitable flow through it. Might be worth investigating if yours has the same.
--
Cheers,

John.

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If you run the shower without the chrome insert when the area is empty, does the water drain away OK - if so, the problem is with the chrome thing, so I would probably replace it with a normal one.
If not, it's in the pipes. It's possible that the water drains when you take the chrome thing out, because the reduced resistance allows the pressure of the water to create a syphon effect, (a bit like a toilet). I have to do this with my shower because the drain pipes do not have enough fall, (It's a long story, and will be fixed in the near future).

If this is the case, I would just dump it and not worry how it works <g>

--
Richard Faulkner

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    On this drainage problem, I noticed in a shower today that the large(100mm?) chrome drain cover had a couple of holes in it, 3mm and 7mm diameter, about 25mm or so in from the edge.
    Regards     Capitol
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replying to Derek ^, CAROLINE WATSON wrote: I am having exactly this problem......beautifully tiled bathroom.... I do recall plumber saying a part was missing from the shower waste pack I bought in b and q......all vacuum plastic pack sealed and unopened. Since tiler was in a hurry to start.... a wastevpart..... the outer cup bit... I think..... was installed. Shower works fine if a human is in it moving about and varying water flowing into trap. If you go away while waiting for hot water to come through.... tray becomes flooded. Plunger rectified matter and when chrome lid and bit of white pipe attached is removed.... drains perfectly fine. What is wrong then with the obviously incompatible parts?.... come on.... it's only tubes...air ... water ... and gravity. Do I drill holes in that white pipe that sinks into the trap? Water drains down via the rim of the chrome cap part. There are 5 wee air holes in centre of this... and they are clear of water level..... until backlog starts.... then tray fills.
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On 22/09/2017 12:44, CAROLINE WATSON wrote:

Are you talking about the type of shower waste that has a chrome dome that the water has to flow under? If so I had this problem until someone on here told me the dome is intended to float up when the water deepens thus allowing greater flow. I then discovered grit (probably from the original tiling work) was preventing smooth movement. Once thoroughly cleaned and the embedded grit polished away it drained perfectly.
Mike
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On 22/09/2017 12:44, CAROLINE WATSON wrote:

Is there a specsavers anywhere near you ?.
You are replying to a post made in 2005. Derek might be dead by now for all we know.
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