Hi all, Puma 80 ,since I have come back from week away has developed a constant noise, hard to describe but a light droning noise,fumes are being expelled from the flue and a noise from the flue indicating boiler is on but not as loud as it would be at full power. The boiler is NOT being used when this happens,no hot water or ch being used. If I switch off the electrics the noise stops. Any thoughts?