The shower tray now does not leak! The sealant did the trick! We made the roof for the shower cubicle and cut out a small opening to insert a polycarbonate plastic sheet to act as a light source. This and the shower tray were giving their first coat of varnish.
The cold water valve was changed over from the straight kind to a right angle type. That is ok and the water is now back on.
We have all the plumbing bits to assemble the heat exchanger now so that is the next job.