How to unlock soil stack inspection cover

[r_c]

Sorry for the stupid question but could someone please tell me how to open this inspection cover.

I can twist it about half an inch (anti-clockwise) and see that it has some kind of locking mechanism. But I cannot figure out how to unlock it. I see the "locking screw" text, but cannot figure out what I am supposed to do. I tried sticking a small screw driver into the hole and pushing, but it made no difference.

20180326_203456

• r_c
• 26 Mar 2018

 

[Madrab]

Once it's twisted anticlockwise to the unlocked position it should just pull off.

It has locating lugs that when the cap is twisted clockwise they engage, anticlockwise to disengage. The screw is added after to make it tamper resistant.

 

[r_c]

I've just come across this question by me, and thought I would follow up. The plumber ended up coming round and he couldn't open it either. He looked at it and thought that something might have knocked it - there was a bit of plastic had broken off. As he was working on the soil stack he replaced the inspection cover and it now works.

Thank you @Madrab for your help.