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?

If the boiler was not designed to have a pump overrun feature is there a
control available which can be added retrospectively. e.g. is there a timed
control available which will allow the pump to run for a short time after
each switch off?

TIA