I've recently moved into a house with a 7 year old Halstead 55 wall mounted
boiler supplying an ordinary tank fed hot water and central heating system.
After a while, when it all starts to heat up, the boiler begins to make a
wailing type noise which can be heard all through the house. It stops as
soon as the boiler stat kills the flame and if you set the stat lower it
doesn't happen. The pump seems to be working fine and the problem's worse
if it's just heating hot water rather than the rads as well. This implies
it's related to either the boiler heat exchanger temperature or the
temperature of the return flow.
Anyone got any ideas how to fix it or where to start fiddling, I want to
turn up the boiler stat to get the rads hotter but at the moment I can't
without the kids thinking the house is haunted.