New shower tray not draining - have some ideas, but need help!

Hi,

I've just installed a new shower tray and power shower (I'm a DIYer rather than professional!). I've not touched any of the existing pipework under the floorboards.

When the shower is working at it's maximum flow rate, the tray fills with water and takes a while to clear - essentially it seems that the existing pipework can't clear the water quick enough (the old shower was pathetic which is probably why I never had the same problem before). It seems stupid to just accept that I can't use my sparkly new shower on it's max power, so I'm trying to work out a solution...

The drop of the wast pipe seems acceptable - the total length of pipework under the floorboards is 3.8m and drops by 10cm (so approximately 25mm drop per metre of pipe). The pipework has to go around 2x 90 degree turns in the first metre of pipe, then runs straight out through the wall. Once outside the wall it does a 90 degree downward turn and joins into another 40mm pipe (along with the bath and sink wastes) for a metre or so into the stack (so essentially the water does 2 90 degree turns inside the house and 2 outside).

Any suggestions?! From scouring the forums all morning, I can see 2 possible was forward, but need some advice!

1) There is probably scope (with a lot of hassle) to drop the pipe inside the room by another 5cm or so. This would then place the shower waste pipe below the height of the existing exterior pipework so I'd need to run a new external waste pipe into the soil stack - this would allow me to create an even steeper drop off in the last stretch of pipe if that would help?

2) reduce number/ severity of the 90 degree bends. If I drop the pipe as suggested above, I could elimate one of the turns on the outside of the house by removing the 90 degree turn (i.e. set the pipe to enter directly into the exterior pipe rather than doing a downward turn first). I might also have scope to reduce the severity of two 90 degree turns under the floorboards.Is this likely to help, if so what sort of thing do I need to create a sweeping bend? flexible/concertina pipe?

Another thought, would I gain anything from splitting the flow into 2 pipes using a 45 degree branch tee to allow the water to flow away through 2 40mm pipes rather than just the one? because of the way the original pipework is cut through a joist, I couldn't insert such a split until after the first metre (where the 2 right angle turns are). Would I gain anything if the water still has to go through the first metre in a single pipe?

Help! I've been working on this bathroom project for over 2 months now and I thought the end was in sight!

Thanks!

The old pipe is probably full of scum.

What waste and trap have you fitted to the tray ? some can be very restrictive. Make sure its a high flow type. Otherwise you may have a load of old scum and rubbish in the pipework, well worth replacing with new and possibly upgrading to 50mm if possible, thats a long run in 40mm especially with other pipework feeding into it. Also make sure you dont have any sags in the pipework , it needs to be well supported at a steady fall.

If you havn't already done so I would pour .5 ltr of Knockout drain cleaner down the waste. This is amazing stuff for cleaning old pipe work and I use it if I'm using existing waste pipes on new showers. Also check that the trap is up to the job by removing the inside pipe ( the one you remove to clean the trap) and running the shower flat out. If it flows ok without it then you know its the trap at fault. Some shower traps can be improved by cuttin 10mm off the length of this pipe.

drain cleaner and a turbo shower trap.

sounds like your pipework is satisfactory so its either a cheap shower trap or sludged up pipes!

Tend to agree with posters about sludged up waste pipes being the most likely culprit old shower with poor flow rate obviously didn`t help trip to local plumbers merchants for drain cleaner MAKE SURE YOU READ INSTRUCTIONS CAREFULLY good luckregards turnpin

agree with nick h ,if the tray is from one of the large chains you probably have a standard waste outlet. when using a power shower you need a high flow waste and trap in the tray and a dedicated waste pipe preferably 50mm on long runs