Vaillant TurboMax Combi hissing noise

[jonbarrett]

My Vaillant Turbomax combi is eight years old. When the central heating starts there is a hissing boiling noise from the burner chamber. It sound like the water is boiling in the heat exchanger pipe. It lasts for a five or ten seconds then settles down and it is then silent. I\\\'m sure it did not used to do this. Any ideas?

[rob884]

The heat exchanger may have slight scale build up and causes a kettling noise. You can add a silencer chemical but i beleive this just gets rid of the noise doesnt actually get rid of the scale which is very difficult.