When my 24i turns on it works correctly, i.e. heats and quite
After about 1 minute is starts to crack snap and pop, rather like loud boiling water in a kettle, this last for about 5 minuets. It then goes quiet and heats silently unit the next cycle starts
I assume this is something to do with the pressure, approx 1.7 to 2.5
Any ideas as this noise is horrid especially during the night,

Paul, November 2010

Nothing to do with pressure, but for the noise description, well spotted, it is actually known as 'kettling'.
Either the pump is not running correctly, or the heat exchanger is scaled up, rather like a kettle gets, but more expensive to correct.

Try adding an internal de-scaler such as sentinel x200 (there are also other makes) which may help, it's a £15-20 gamble, if it works, great, if it doesn't, you're into a new heat exchanger.

Carefree, November 2010