My system (C Plan) has two pumps, both for central heating, seems who ever installed the system was unaware a pump will pass water when switched off.
I am sure the idea was when heating was wanted for zone 1 (the flat) then just zone 1 pump 1 ran, and when zone 2 (main house) then pump 2 ran, and if no pump runs, then just domestic hot water (DHW).
However when only one pump ran, the other zone was still heated by the water circulating in reverse direction.
Again in theory if all the TRV heads are closed then still can't circulate, but setting up the times on the programmable TRV heads to stop heating did not really work. And the TRV heads in the flat were not programmable type.
So answer was fit motorised valves which in turn switch on the pump, but then you need a pair of micro switches in the motorised valve one works the pump the other works the boiler, since motorised valves only have one micro switch needed a relay with two sets of contacts so one turns on pump and other boiler for each zone, other wise no way to turn on one pump and boiler.
At the moment still not fitted second relay, so zone 1 will not heat up unless zone 2 is running, and since we hardly use the flat in winter it is not really a problem.
But to work it all out only option is make a drawing. This
was one of the many drawings made while working out how to wire it up.
And after all that there is a fault, not sure where yet, with no radiator really hot, I am getting really hot return water which is turning the boiler off before house if fully heated, how hot water is returning is a mystery. Maybe some by-pass valve I am as yet unaware of?
Tracing I seem to have
this layout, but it seems the garage was turned into a flat, and when this was done wires and pipes were hidden, I found a whole fuse box still in use between the new false ceiling and the original garage roof.
My major problem was there was a three core and earth cable between main house and flat starting red, yellow, blue and becoming brown, black, grey and one core open circuit. So question was how to control CH and DHW with just two wires, my way around the problem was to use Nest Gen 3.
There is always a way around the problem, but you want some thing others can understand and fix, I had a few spare PLC's (programmable logic controllers) and HMI (Human machine interface) and I had the skill to install them and program them, but now 70, so what happens when I am 85 and some thing goes wrong? Could I fit it then?
Best answer would probably be a repipe to use one pump and 2 motorised valves.
Having had same problem I would agree.
If you retain 2 pumps you have to use relays to separate live feeds to boiler and pumps.
Easy enough to do common system on older oil boilers.
Likely correct, but the two guys who came to do the plumbing on mine both admitted they had no idea how to wire up. One called himself a plumber, the other a heating engineer, all oil around this area. There are some very clever guys where I work who look after the boilers at work, but they expect a boiler to produce steam, and in one case super heated steam, if it does not boil the water they think there is a fault, the central heating in the carriages is a total loss system, steam fed from boiler and water drips out of last carriage, this may look good at Halloween 2019 from a railway carriage
not though how I want to heat my house, prefer it if my boiler does not boil the water.
