Bath/ shower not draining

25 Jun 2014
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United Kingdom
Dear all,

I had a bathroom fitted a few months ago and would like some opinions regarding what may be wrong with my bath drain before I get the plumber back for one of many snags.

If I pour around 500ml of water into the bath it starts to back up, and then drain very slowly. Likewise, if I have a shower, the bath starts to fill up until it's about an inch deep and then seems to drain all at once.

When the plumber fitted it he said the bath was slow draining and blamed the waste pipe already set in the tiles which runs under the floor (apparently slightly narrower than normal). He told me to use lots of sink unblocker. However, the old bath did drain, and this problem has only come about since the new one went in.

I can't see under the bath, but is this an airlock/ or perhaps not enough fall on the drain? I do know the plug hole is a the top end of the bath but the hold to existing drain is around 1/2 way down the bath. I've used lots of sink unblocker with no results.

I'm asking as I know he'll be reluctant to take the side of the bath off but I really don't think it's a block, I've dealt with that sort of thing many times before. He's already come back for a leaking sink drain and a mis set tile which keeps coming loose.

Obviously not massively happy with this job :confused:
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Incorrect or insufficient fall of the waste would be my first guess. Only visual inspection will tell you for sure.
Thanks very much for the reply kbdiy- can I ask, what is normally considered suffcient fall, and does it matter that the plug drain doesn't go vertically down into the tiled floor to the drain, and essentially will be a diagonal pipe which goes from the plug to the floor level?

Thanks again, much appreciated.

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I can't remember the exact figures for a recommended fall, but if there is a visible fall then it is reasonable to assume that it would cope with the small amount of water you have been testing with and not back up as it seems to.

You say the shower causes water to flow back into the bath before draining away? Could be the way the 2 wastes join together before entering the existing drain but only visual inspection will give any clues. Anything else is just guesswork.

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