Had same problem. Vaillant will come out and tighten nuts on heat exchanger and the noise will stop! They know about this issue. The Vaillant tech told me they are picking up the problem as they go along.
I have a new Vaillant as above which does not fire up first time and clunks three times as the gas valve opens, shuts and opens again and it fires up second attempt. They have told me this is normal so I have submitted formal complaint to the dispute body. I'll never buy another Vaillant. It's been a nightmare since October 2022! Good luck!
I have a new Vaillant as above which does not fire up first time and clunks three times as the gas valve opens, shuts and opens again and it fires up second attempt. They have told me this is normal so I have submitted formal complaint to the dispute body. I'll never buy another Vaillant. It's been a nightmare since October 2022! Good luck!
