I have been changing a bathroom suite, however after installing the hot water does not seem to come back on. there are two stop valves in the flat, one for mains supply & another which supplies the cold to the bathroom from a tank I presume at the top of the building. the cold water to the bathrooms is ok. I am sure the mains stop cock is not faulty as there is is water supply to the kitchen sink. The hot water is fed to the bathroom from the mains via a combi boiler. Is there anytghing I can try?