Thank you for that speedy response John.
Since posting my question I have talked directly with the manufacturer's
engineer. He listened attentively to the problem and suggested the most likely problems and solutions.
With his advice and the product booklet I managed to dismantle the valve and...
Help.....
I recently purchased an Opella Castalia Cisterns from Screwfix.
The unit came with a Torbeck compact bottom entry valve pre fitted.
Also prefitted was the Torbeck variflush drop valve.
Pleased that all the innards were already in place I set about mounting it and fitting the...