I have 2 problems at the moment one with my mira 415 shower which is connected to my halstead gold combi boiler. Sometimes it will not give any hot water and is running really cold it doesnt happen all the time but is getting worse. The burner on the boiler doesnt kick in. I have tried turning on a hot water tap which starts the burner and that then starts the shower running hot but as soon as I turn the hot water tap off the shower goes cold. the pressure drops as well when I turn the hot tap on. So lots of cold showers lately I would have a bath but that hot water tap after I have turned it on works fine but then after say 5 mins the water drops until none flows at all. Any advice would be appreciated.