Could heating systems be improved with this idea?

[BigBurner]

Vitodens 100 Compact

That figures. Nice.

 

[D_Hailsham]

If CH was satisfied and HW was still calling, then yes, it would turn the valve to HW. Or vice versa.

the makers tech dept told me that, when both calls are satisfied, it stops firing, and leaves the pump on the timed overrun with the valves at whatever position they were previously at.

You say "valves" do you have an S-plan (two 2-port valves) or Y-plan (one mid-position valve)?

Edit: Just had a read of the Vitodens 100 installation manual, which shows a Y-plan with two 2-port valves!!! Makes you wonder ...

I can see this working with the mid-position valve, but not with the 2-port valves, which shut as soon as power is removed.

There is a 'quirk' in the design of the MPV which means that the HW port will stay open when CH has been satisfied from the CH only position. In this case the overrun will send the water through the rads

But if the valve was in mid-position and CH goes off, for whatever reason, the CH port will close, leaving just the HW port open. When HW is satisfied the boiler will go off leaving the HW port open. The overrun will then send the water through the HW coil - not through the radiators.

In both cases there is somewhere for the water to circulate - hence no bypass necessary.

 

[JohnD]

I have a Y-plan

 

[D_Hailsham]

I have a Y-plan

Thought so!

In which case, the overrun will go through the rads (provided the TRVs are open) if the valve was in the CH only position. In all other cases it will go through the HW coil.

 

[JohnD]

and a 3-port valve.

the cyl heats up quite fast so HW is seldom on.