Help ! Slow running shower trap/waste.

[griffic]

Help. I've just replaced a shower tray as part of a complete bathroom refit. The water is backing up in the shower tray. If I use a plunger on the trap I get air coming out and then the trap runs great creating a good flow and works fine. However, as soon as the shower is turned off there is a gurgling from the trap and if the shower is turned on again the water starts backing up immediately,(but will clear if a plunger is used.) The shower valve is fed by a combi with reasonable flow but nothing ridiculous. Its got a 90 mm diameter waste/trap connected to 40 mm diameter pipe that runs for approx 500 mm level(little or no gradient.) then to a swept bend about 400mm away with reasonable fall to a second swept bend then approx 2000mm where it exits the house with a third bend and then has significant fall for about 500 mm into a hopper(i.e. 3 bends in total.) There are no other connections to the waste pipe. The customer claims it worked fine before the new tray - I've added about another 300 mm of pipe and one swept bend - however the original installation had a deep 'P' trap attached. I've removed the trap and tried running water through it - it works fine. I've cut into the pipe between 1st and second bend and pipe is clear between trap and this position and also between this position and hopper. I'm stumped. Do I try a different trap or try to modify pipe run( major headache) ? Can anyone recommend a high flow trap? The one that is fitted was purchased by the customer and is an 'unbranded' one

 

[lame plumber]

air locking, drill a hole in the trap top if all else fails, had to do that before, then 6 months along they discovered the sewer had collapsed

 

[griffic]

Thanks for suggestion but water backs up if trap top is completely removed and also if white tube is removed from inside trap.

 

[chris watkins]

Back fall causing water not to run away, when you plunge you are causing it to self siphon & so as hopper is lower it will drain well sucking all water from trap, break siphon & it is back to square one.
Got to say, if it was a complete bathroom why are you still using the hopper ? should be going direct to stack !!

 

[Chalked]

If it runs ok when you remove the trap top.
cut 10mm off the bottom of the tube. Sometimes it's too close to the bottom to allow water through.
7a on this pic.

 

[Ch4 plumbing]

I agree with Chris, you should really have considered upping the waste size too, with what you've allowed in pipe length your just under 4m Exclueding fittings which Is too long for 40mm waste pipe without a vent, adding to that it's a shower so your starting with less fall at the start.

 

[griffic]

I went back to job today and discovered the cause of the problem. The original 2 metre length of pipe had a large sag in the middle that was holding water. I replaced it with 50 mm pipe, as suggested by CH4 plumbing. Thanks to everyone who replied.:clap: