Alex Duetto random water hammer noise on heat up

[artman]

Hello CSers

I have noticed at times (random), during heatup of the Duetto II that there is a knocking noise occurring during the heat up phase of the machine. The noise would be best described as water hammer, what you would hear in some homes if shutting off the tap quickly.

The noise occurs every 1 to 2 second intervals, both before and after the steam boiler is pressurised. Running water through the group or purging the steam and water taps makes no difference. sometimes there is a few seconds gap between the noises. Sometimes it doesnt happen at all. Once the boiler is pressurised the noise stops after a bit.

The machine operates perfectly otherwise.

Any ideas on this mystery noise?

Cheers

[MrJack]

Possibly "bumping" - happens during rigorous localised heating when pockets of water become superheated and then suddenly boil.

My Bezzera makes similar noises and I suspect that this is what it is. Seems to be more common of late actually.

https://en.m.wikipedia.org/wiki/Bumping_(chemistry)

[artman]

thanks for the info, that could be plausible. Weird that it doesn't happen all the time? Might pull the cover off during heating and try to locate the source, you can feel the "bangs" transmitted to the body of the machine. Never experienced this in any of the other machines I have had.

Cheers