"Ewan MacIntyre" wrote in
message ...
Malcolm H wrote:
I have a Glow-worm Fuelsaver 40-50 conventional flue boiler which was
installed in 1984.

Everything works fine except that the central heating circulating pump
stops
running as soon as the room thermostat reaches the desired temperature.
This results in some noisy bubbling from the boiler as it overheats for
a
short time after the room thermostat switches the pump and boiler off.

Does anybody know if this boiler was designed to have a pump overrun
feature
to avoid this problem?


How bizar I've been wondering about exactly the same problem, with my
Glow-worm Hide Away. It's slightly younger than yours, possibly 1986 or
so.

I think it's quite wasteful to have all that recently-heated water
suddenly come to a halt, rather than circulate it for a short time to
spread it around. Also, as you mention, it causes kettling which must in
turn reduce the life of the boiler by a small amount each time.

I've considered building my own overrun feature using a mains powered
relay, a microcontroller and a solid-state relay, so that when the
system turns the pump on, it is actually just indicating this to a
microcontroller, which will delay the turning off. Like so many similar
ideas, it's in my head rather than built...

Ewan

I too have a design in my head but it only requires one power diode
(rectifier), one resistor, one electrolytic capacitor and one relay.