low hot water pressure in combi boiler - plenty col

egar

Hi - new combi boiler fitted over 1 month ago - all working great till Friday - hot water pressure really low (temperature still fine though) - cold water pressure is as normal. Heating working fine too CH pressure bar thingy sitting at 1.5 which is correct. Only thing I can think we've done to upset it is filling up a new garden pond with the hose - did take a long time. Any thoughts before I call out the plumber man (although he's very nice and helpful).