faulty pressure on cistern flush switch

[GBZ]

I've come across a cistern, inbuilt behind a tiled stud wall, that has an air pressure switch to operate the flush.

This seems to have stopped working. Access is via a letterbox shaped hole at the top, but apart from giving me a view, there doesn't seem to be any more access.

Any ideas on how to fix?

Thanks

 

[easyt]

Make a bigger hole? Is it accessible with cistern removed ?

 

[GBZ]

Have now fixed it.

Removed front button and lo and behold, there was a hole in the air pipe. replaced, refixed and voila, job done!

Thanks for response.