Whisteling/screaching noise when boiler is firing

[ewans]

All,

I'm hearing a noise when my boiler fires up. The noise is like a *mix* of car brakes screaching and a kettle boiling. Also there is a small leak from the underside of the bolier when its cold, this stops once its been running for a bit.

The noise lasts for longer when the bolier first fires up from cold.

Once up to 80' or so the noise is only there for 5-10 seconds when the flame first lights then it fades away, the flame and pump are left still running with no noise.

The noise is does not happen 100% of the time when the flame is on.

The CH and HW work fine, no loss of performence etc. since before the noise started.

Boiler is a Saunier Duval Thema F about 7+ years old.

Any suggestions on what this could be?

TIA
e

 

[ewans]

should have said its a combi boiler and I live in Glasgow which i think is a "softish" water area.

after finding the FAQ's seems like this is a case of "ketteling"

but with the addition of the leek does this suggest the heat exchanger is also damaged?