Limescale

One of the showers has been playing up. It became almost impossible to turn the water on or off and to adjust the temerature. GF phone his trusty plumber, but he would not countenance coming to fix it. GF eventually contacted the manufacturer and their service engineer turned up. 

They will only do the work if the water to the shower can be isolated. GF had crawled into the loft space to turn the isolation valves. They, however, had evidently been equally affected by the limescale that was (no doubt) the source of the problem.

WD40 would not shift it

GF's scredriver would not shift it

GF's BIG screw driver would not shift it.

The only solution was to take drastic action. The main stop cock for the house was switched off and all of the taps opened. The tanks emptied and all was ready when the engineer arrived. Needless to say the maintenance took about 5 minutes, and cost a lot of money. The shower is now fixed and all is well.