IMM wrote:

Maxie, will reveal if it actually "pulses" the pump. What length a pulse
is, is open to interpretation.

I reckon what I need is a relay with a time delay off (for the overrun)
with the coil wired to the boilers Switched Live (ie the input from the
valve microswitches). If I wire the pump to the relay's common, it's n/o
to a permanent Live and its n/c to the Pump Live then it should works as
desired. The only thing that concerns me slightly is that in the
boilers fault Finding Guide it suugests *intermittant* lockout can be
caused by Pump Live and Switched Live being connected - when I did it,
it locked out straight away.