In article , anon wrote:
My Vokera Excell 80E combi boiler occasionally starts whistling when
the central heating is on. I can stop the whistling instantly by
turning on a hot tap for a couple of seconds. The whistling goes away
but always comes back at some point. Some days it will come back in a
few hours, other days it won't whistle much at all.

Please can you tell me what the problem might be and also what to do
to fix it.

Ours does this all the time until it's warmed up. It sounds like a
hurricaine in the kitchen until about 15 mins into a cycle then it
quietnes down. It's been regularly serviced and checked and double
checked - it just does it.

There's a fair bit of noise from the gas influx to start with - but it
clanks and whistles while it gets up to temperature and two separate
engineers have told me this is safe and ok to use....

Might try some of the stuff that Ed suggested tho - was reading about
it...

Cheers
Dan.