Ed Sirett wrote:

I would have to take a look, but the only wire I know about running up
to the cylinder is to control the pump. This is via a fused switch, so I
suspect it is just a mains wire coming up from the timeswitch. I am not
100% sure but I do not believe there is any pump control coming from the
boiler (a Baxi Solo 3/50 PF); I think the switch just turns the both the
boiler and the pump on or off (the pump runs constantly when the system
is on). I wouldn't be surprised to crack it open and find both the
boiler and the pump appliances wired to the same terminals.

OK. Looks like it's a broken install. The Solo 3 DOES operate the pump
directly from the boiler. So it look like you'll need a multicore from the
airing cupboard to the boiler.

Thanks for the reply, Ed. I need to check exactly what way this is
wired, but should I arrange to correct the problem if the pump is not
being controlled from the boiler ? Or put another way, if the system is
wired up correctly then what would I lose/break if I controlled the pump
from the programmer instead ?

The objective here is to avoid running any additional wires between the
pump and the boiler. Though, if push comes to shove, I could have a
check to see how easy this will be. I don't know if they have just
plastered the wire into the wall, or if there will be a duct - if
they've put a duct there then it should be nice and easy.

So my idea is, instead of sending the mains signal up to the pump, I can
just send the mains down to the boiler. That may involve ensuring that
an appropriate mains ring is available. Would it be really stupid or
non-compliant to try to get away with hanging it off the same ring that
the immersion heater is on ? Having an electrician in to run another
ring up to the cylinder would override my objective of avoiding having
to rip out walls or tiling to do wiring.

The actual load from the boiler, pump, valves etc is under 1 amp.
It is quite common and I beleive compliant to run the heating from the
immersion 15A radial circuit.

That clears that one up then, thanks.