"Velvet" wrote in message ...

If it's an additive in the gas supply, that gas guy told you wrong. The
diverter valve (or hot water flow sensor/diaphram is nothing to do with the
gas supply so it matters not what additives they put in the gas. If he was
talking about additives in the CH system - that's a different matter, and he
*could* be right. I've had a diaphram go in my old combi in the 9 years I
had it. AFAIK it had no inhibitor added - certainly the colour of drained
water from the system shows no sign of inhibitor (I bled the rads fairly
early on in the system's life).

Velvet

Your point makes sense. This is a 2 year old Ariston boiler. No
inhibitor either.

The Ariston boiler 'sings' at the flue outlet, quiet but high
pitched, which'd put me off buying another one.

Tony