Erratically draining shower

[Lower]

I seem to have an odd problem with the shower waste.

When the shower is first turned on for the first time in a day the waste is extremely slow to drain, to the point that the the shower tray fills up and threatens to over flow.

Lifting the dome on the trap and lifting the hair trap (which is clean) lets the waste start to do its job and the water starts to drain. The waste can them be put back together again and the water will continue to drain properly.

What is odd is that the shower can then be left to stand without the water running for up to an hour and the water will still drain correctly from the start without going through the rigmarole of lifting the dome and hair trap.

Any ideas what might be causing this and if there is anything i can do about it? There is no access to the trap under the shower tray without removing the tray from the shower or going in through the ceiling below.

 

[John506]

Might be worth giving it a good plunging

 

[Space cat]

What is odd is that the shower can then be left to stand without the water running for up to an hour and the water will still drain correctly from the start without going through the rigmarole of lifting the dome and hair trap.

What happens if you leave it longer? Does the problem come back suddenly of gradually? I'm suspecting an airlock in the drain, possibly due to a sagging pipe.

 

[Nige F]

Yeah, definitely it's an air lock problem. Don't worry just consult a good plumber in your surrounding. It is really not a tough task for him to execute.

Just tough finding one

 

[Lower]

Thanks for the replies.

So what is the likely cause of the airlock? Not enough fall or droop in the pipe? The run of the pipe is only around 1m before it falls into the waste stack.

Access to the pipe would only be through the ceiling below or via the outlet so its going to be a pain to get at to address.

 

[Nige F]

Have you got an air admittance valve ( durgo) on the top of the waste stack ? If so take it off and see if that makes the shower better . A 1 metre run of waste isn`t long - try some drain cleaner , but not a strong acid one - that will make the pipe heat up and bend if it isn`t supported.

 

[Lower]

No air admittance valve because the top of the stack is open. Its a 1950's house. Nor is blocked judging by the draft that was coming out of the toilet waste when i had the toilet off recently.

I'm starting to think that the airlock is being caused by design of the domed trap itself as it flows fine with the top removed. On closer inspection it looks like someone has drilled some holes in the top of the dome for this very reason.

 

[HERTS P&D]

Fit a new shower tray trap and go from there.

Andy