I've just had an unvented hot water cylinder installed in my bungalow. The boiler is an oil fired worcester bosch danesmoor 20/25 it is an open vented system. The original indirect cylinder was situated next to the boiler about 6" above it. The system top-up tank is in the attic. There is no 3 way motorised valve only a circulation pump. The unvented cylinder has been installed in the attic & the system fill tank lifted to 1.3 metres above the flow/return pipework for the cylinder. Any suggestions as to why there is no hot water. The flow/return pipes to the cylinder only get warm about 2-3 feet above the boiler. Any help appreciated.