Please help. Slow drainage from bath tub

[frembrit]

Our house is about 22 years old, and I dont think the drainage from the bath tub has always been slow, though the last few years I can remember, it has been slow when draining after a bath.

We had a mixer shower and new boiler installed recently (previously there was no shower and only a hot water storage tank) and the flow rate now is quite fast. The drainage from the tub seems very slow and within 30 seconds of running the shower, there is a build up of water in the tub (so I'm practically standing in a puddle).

The drainage from the sink basin is fine, I guess it's because it is higher up. But there is a gurgling of air from the bath tub after the water has drained from the sink. Also, if the sink is full and the plug is pulled, the water drains away quickly but it also starts to come up into the bath tub. The sink has a standard plastic bottle trap and the tub has a U bend type trap. Both join the same waste pipe which is almost horizontal and not much lower than the height of the drain hole of the bath tub.

Is it because the pipe is running horizontal that is causing this or is it the fact that the pipe is not low enough?
Or another thought is that the main stack is not breathing properly, hence the gurgling air sound after the water has drained.

Thanks for any help.

 

[breezer]

its only a guess, but i would say its as you said " the horizontal pipe"
when the flow was slow the water could meander down the pipe no worries, now you have niagra falls it can not all get away fast enough.

similarly when you unplug the sink the water can not get away fast enough so it comes back up into the bath.

There may also be a slight blockage where they meet the outside pipe, i.e. hair and shampoo
i would take the pipes apart and make sure they are 100% clean / clear

 

[Bahco]

Check for blockages first.
If not could be incorrect gradient/ pipe sizing or air admitance valve needed.

 

[ChrisR]

The stuff which really sorts out the hair problem, which is very likely to be a factor in your problem, is sulphuric acid. You can buy it in plumbers merchants, as drain cleaner. It dissolves hair, and quite a lot more besides. DON't let it get to any "gold" things or a bath surface(steel baths are OK though). I use a funnel to get it in the hole. It works fast.

Absolutely never let it mix with Hydrochloric acid, "Spirits of salts", sodium hydroxide, caustic soda, "lye", or any bleach or other cleaning agent. Never add water to acid, only acid to water. It's ok to flush the drain with water after treatment though, just leave the tap on!

If you don't fancy it, first pour a LOT of BOILING water down the hole, it will dissolve soapy goo quite well. If mechanical clearing isn't an option, the Mr Muscle drain cleaner isn't bad because it's thick.

 

[frembrit]

Thanks for your help.

Unfortunately it's still the same. I've tried the boiling water method as I dont fancy doing the sulphuric acid method. I've also tried mr muscle and other stuff.

I did find an inspection cover in the cupboard which allows me access to the main stack/soil pipe (whatever it's called) I tried to take off the round inspection cap on the pipe, but I couldn't fully remove it beccause the plumber who fitted the boiler has drilled a hole into it and put a plastic pipe through it, which comes from behind the stack acting like a clamp. I take it that it's a overflow pipe as it is a condensing boiler? It looks like the plastic pipe uses push fittings on the bends and joins, if I can remove this pipe I can remove the cap. I tried pulling on it, but it seems very tight (plus there is not much room around the stack to get much of a grip on anything), anyone know how to remove/unattach plastic pipe??
I am hoping to get the cap off so I can check for blockages in the stack.

I dont think the waste pipes from the sink or bath are blocked as I can hear the water run down quite fast initially and then it slows down when it gets nearer the stack.plus the bottle trap is clear and as too is the U bend under the bath.