I have a Baxi combi 80eco which has a problem - when I turn the hot water on it starts to heat the central heating at the same time. The only way I can seem to get a good flow of hot water is if I put the central heating on and wait for this to fully heat up. I have checked the Hydraulic Outlet Assembly and both pins seem to be working ok. Can anyone give some idea what the problem may be and how I can solve this.