I will start by saying I am not a plumber but I have learnt loads thanks to people on here. I am currently having an issue with heating & Hot Water. It is working but I have to do certain things to make it work each day. The question is about the 2 gate valves in the picture. Valve number 1 and 2 . I think from what I have looked at on google etc that 3 is the pipe taking hot water from boiler into the immersion heater which is on the left (we have an open vent system). The pipe under Valves 1 & 2, I think, is the cold water out of the heater back into the system? Should both valves (1 and 2) be open or just valve 2? When both are open quite a bit, it sounds like air is getting into the system and at that point the boiler stops. When both are closed, the pipes around the house make a loud clanging noise. As a result, to get Heating, I currently have to close both valves and the heating is fine. To get Hot Water only, I have to open both but only a little and sometimes this fails. My thinking is that of Valve 1 is open it is letting cold water into the hot water coming from the pump and that causes the issue? Currently, I cannot get both Heating and Hot water to work at the same time. Nightmare. The rads are hot around the house (all 14) when heating is on and when the water works it's fine - but it is rather hit and miss. I am convinced the issue is to do with the valves, especially valve 1. For info, the pump is currently on PP1 not CC3 as in the picture. Thanks!