yes by turning the power off to the boiler it has stopped the noise and the smell has stopped.
the wall under the sink is lined with insulation which has some sort of chipboard over it and then the pipework runs over that. on further inspection (ie after pulling out all the pots and pans!)...
Hi
I have a Puma 80e boiler which over the last week had been making an intermittent hissing noise.
The noise got more frequent so that everytime I was in the kitchen I would hear it and it seemed to happen whether the boiler had just been used or not. So I decided I didn't want to leave...