OP
Chris M
It sounds like it's wired up as a gravity system, hot water fires the boiler and heating operates a pump.
I'd say you'll need a decent plumber and electrician to work out what bodgery has been done and how to fix it.
Booooo feared that might be the case..
In any particular order or find two guys and get them both to rock up at the same time?
Would pics on the wiring near the cylinder help at all or too much to remotely diagnose?