Roger R wrote:

Now, using the bottled water it doesn't make any noise at all until just off
boiling, but even then its much less than before. I can hear the radio
again. So I think the noise is made much worse by hardness in the water,
making a very thin - invisible micro scale layer on the element, but why
that should be make the noise worse...? Something to do with the breakdown
of the temporary hardness of the water during boiling perhaps.

It may be that the scale adds roughness to the surface which acts as a
seed site making it eaiser for cavitation to occur....

--
Cheers,

John.

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