I have a gravity fed hot water system. Until recently it had a health
system presssure. No changes have been made to the system and no recen work has been carried out. Pressure has dropped off to the point wher it can take 20 minutes to run a bath. There has been a correspondin drop (although not quite as significant) in cold water presure Pressure starts good and tails off as if a down pipe were emptying bu not being backed up.
All valves feeding the header tanks seem to be open and depressing th ballcocks results in appropriate water flow into the tanks
-- kipper