I'm a bit puzzled by your reference to a pump connection on the boiler.
This
normally only applies to fully pumped systems, and keeps the pump running
for a bit after the boiler has stopped firing in order to stop the
residual
heat in the boiler's metalwork from causing it to overheat. With a gravity
system, the boiler needs to be able to take care of itself in HW-only
mode -
where the pump doesn't run at all. Are you *sure* it is a gravity system?
If
so, please clarify how the pump is currently connected and what, if
anything, the boiler's pump connection is used for.

Just come down from the loft. It is definatly a gravity system.

The boiler is fully pumped/gravity switchable which may account for the pump
outputs in the boiler wiring.

After a bit of a playaround, as far as I can see if power is put to the Swl
input - just the boiler fires up (i.e we get HW only)

If power is provided to the "L" input then just the pump runs

If power is provided to "L" input AND "Swl" input then boiler and pump run
(i.e we get heating AND water)

As far as I can see the pump is wired directly to the boiler pump output -
with no other connections.