I had the same problem when upgrading my boiler, and I managed to free a spare wire. There were two neutral wires going to the wiring centre in my airing cupboard. (I think from memory, one was from the FCU/programmer and another came in with the cable from the room thermostat to the motorised valve) I disconnected the one from the FCU/programmer and used it (suitably identified) as the switched live for the pump. Then connected the motorised valve to the other neutral from the thermostat.
Or,
Have a boiler where the pump is integral, hence pump wiring also integral, then remove the upstairs pump.
Or,
Take a permanent live from the wiring centre, wire it to feed the pump via a relay that is timed to delay on de-energise and use the existing pump wiring to energise the relay. Then set the relay delay to correspond to the boiler's overrun time. Power to the relay would be lost when the boiler went off, then the relay would open the contact after the run on time and stop the pump. Sketch below.
Or,
Is there an alternative route for a new cable? For example, outside the house, up into the roof and then down into the airing cupboard? You could always relocate it when you replace the carpet next anyway.
Or,
Have a boiler where the pump is integral, hence pump wiring also integral, then remove the upstairs pump.
Or,
Take a permanent live from the wiring centre, wire it to feed the pump via a relay that is timed to delay on de-energise and use the existing pump wiring to energise the relay. Then set the relay delay to correspond to the boiler's overrun time. Power to the relay would be lost when the boiler went off, then the relay would open the contact after the run on time and stop the pump. Sketch below.
Or,
Is there an alternative route for a new cable? For example, outside the house, up into the roof and then down into the airing cupboard? You could always relocate it when you replace the carpet next anyway.
