Hi, my friend has one of these boilers and for ages it has made loud vibrating noise on both Ch a hw. It also suffers from delayed ignite. She has very low funds and aware that a gas man needs to be called as it's very likely the burner needs replacing. The question is the Hammering and I am just trying to work out possible cause so i can source the parts and clean the system myself before he comes if that makes sense. The Hammering can it be the the 3 way valve? It's just weird it effects both HW & CH. And guess the violent Hammering has damaged the burner at a quess?
