I have a Megaflo unvented indirect cylinder, model CL170HE. Unfortunately there is no hot water naturally coming from the system. However I can get hot water by using the immersion switch on the main wall (electricity and costly). I have tried turning up the 2 immersion heater elements found in the grey box at bottom of the cylinder and this has made no difference. It appears that the issue will be one of the following: elements, immersion or valves.