hi guys. Got a small leak on this combi. Coming from the hot water flow valve. There is a short piece of metal with a hole and spring inside. When a hot tap is run it is from here that it leaks. Worried cos the pcb and electrics are close. Is it an easy fix? Do i need to drain both the dhw and heating or just the hot water. Part number would be great. Couple years i changed a worc cdi diverter so willing to give this a go. Thanks. Jin.