Trying to fix a problem on a s-plan heating system. Boiler is working fine, only problem is heating and hot water are not working at the same time. If we turn the heating off, then hot water starts working. Looks like a problem with one of the 2-port valves. The system has got a 22mm 2-port valve on hot water and the lever on the valve goes back to auto when i move it to manual. On the heating side is a 28mm 2-port valve and the lever is moving freely and doesnt go back to auto itself. Can anybody advise please how to find out whats the problem. Thanks