Hello, my potterton boiler fires up for hotwater but doesn't fire up for heating. I believe i have a Y-plan system. I have checked the room stat which seems to click on/off properly. Now also the hot water in the taps have become extremely hot, although i am not sure if this is connected with my main problem. any ideas ?? How should i check the 3way valve (acl lifestyle) if this is what is causing it? Grateful for any advice.