Shower JT90 Concealed Waste Not Draining

[dredd29]

I have installed 3 JT shower trays with the compatible JT90mm concealed wastes. I'm at the end of my tether the wastes always need plunging every few weeks and the trays fill up with water quickly. The showers are standard with 200mm diameter size rainheads, so don't emit excess water. I just don't know what the cause is as I unblock with plunger and the water fast pours down the waste no issues and then two weeks of showers later and its stopped draining again. I don't know whether it is to do with the external soil stacks which have air admittance valves on instead of covers?

 

[Ben-gee]

Try removing the aav, I have found the jt40 to be a good waste - the many turrets make the chrome cover nice and stable too.

I presume you have been putting them in with correct fall and pipe size?