"Paul King" wrote in message
news:1106748399.5029843a500ab4eedfa771debfee4a72@t eranews...
Rick wrote:
Hi,
I've noticed that a couple of radiators become hot even though the
central heating is off when I'm using a hot water tap for some time. I
have an old glowworm combi bolier if that's of any use. Can someone
explain how this is possible? Thanks.

Sounds like the diverter valve which changes the boiler water flow from CH
to DHW isn't closing fully, allowing a small amount of water to flow into
the CH side when it should all be flowing to the heat exchanger to heat
the
DHW.

I don't think Glowworm boilers had valves 30 years ago, (like my reliable
antique). It could be circulation round the CH caused by convection when
the gas is burning a lot and the boiler water is very hot. My hot tank
water is done by convection from the right side of the rectangular boiler
and the CH by a pump from the left side, hence four pipes to the boiler
altogether. It is possible that there is some interaction of the flows in
the boiler.