I have recently installed a replacement shower in my en suite.
I fitted a bottle trap (which came with the Mira shower tray). Problem is that the waste water does not flow properly. Water builds in the shower tray immediately until it is almost overflowing then the pressure seems to change and water is taken away quite rapidly until there is none in the shower tray at all. If the shower is turned off and then back on at this point the same situation starts all over again.
I haven't changed anything underneath the shower tray from the previous set up apart from a new bottle trap replacing a "p" trap. The fall is OK (probably a little steeper than with the "p" trap) and the discharge is into the soil stack.
Once the water starts to drain away it is fine but it keeps getting perilously close to overflowing before it starts to move any water at all.
still mighty puzzled....
Guys, grateful for the suggestions but i'm still without any real progress on this.
If there is a blockage, which disappears when the water is almost over-flowing the shower tray, how can it then re-appear the minute the shower is turned off?
Is there any possibility this could be due to a vacuum being present, which clears when there is sufficient pressure, but re-establishes itself once the flow of water ceases?
I've been trying to get my head around this one ever since you first posted it. All I can think of is that an airlock may be forming in the bottle trap which prevents the shower tray from draining until it's nearly full at which point the physical weight of water in the tray pushes the air out thus allowing it to drain by syphoning through the trap. Then when the tray empties and air gets into the trap the whole cycle starts again. Have you thought of fitting a more basic trap than the bottle one?
"I haven't changed anything underneath the shower tray from the previous set up apart from a new bottle trap replacing a "p" trap."
So is the shower tray exactly the same depth as the old one ?
and the outlet from the trap - at the same height as before ??
If the trap is larger and/or the tray is deeper - could it be that the waste pipe at the shower tray end has been pushed down further than when the last shower tray was in - therefore the pipe rises rather than falling away from the shower tray. The water will not drain away until it becomes level with the highest part of the pipe - once it starts flowing the rest of water could be syphoned from the tray as there'll be a vacuum in the drains in the direction of the water flow.
'grateful for the suggestions but i'm still without any real progress on this'
if you need it sorting quick then a DIY forum probably not the best place to be spending your time - get a recommended plumber to sort it.