Underfloor heating flow and return

[tuck1s]

We have a new underfloor heating system laid in an extension. This requires flow and return water from the boiler.

The existing system boiler provides hot water (indirectly via a cylinder upstairs) and the existing radiator heating. There are 2x 2-port valves, I think this is a classic "S Plan".

We've arranged the UFH wiring via an Ambiente wiring centre to make an independent "call for heat" via its volt-free contacts. This goes to the upstairs wiring centre and is in tandem with the existing 2-port valves that call for heat via their limit switches.

Currently the new UFH been plumbed into the *radiator* flow and return. However I think this leads to a fault condition, where the UFH calls for heat, driving into a closed valve. The boiler registers insufficient flow and over-temp and shuts down.

I think the correct place to tee off the UFH is directly from the boiler flow and return, so that it can act as an independent third zone?

 

[CountryFan]

Yes, to make it work idependently, you need it to bypass the heating circuit and have a motorised valve

 

[Exedon]

Depending on system lay out boiler ect we would create a other zone with motorised valve. Honeywell S plan plus.
Needs care where to connect return ideally before cylinder return.

 

[tuck1s]

Depending on system lay out boiler ect we would create a other zone with motorised valve. Honeywell S plan plus.
Needs care where to connect return ideally before cylinder return.

Is that to prevent reverse flow to the cylinder and rads?

 

[Exedon]

Cylinder return should always be last connection before boiler we always try to make it on branch as well .
Prevents any possibility of reverse circulation or 'heat creap' into rads when only dhw on.

 

[tuck1s]

Cylinder return should always be last connection before boiler we always try to make it on branch as well .
Prevents any possibility of reverse circulation or 'heat creap' into rads when only dhw on.

Thank you. So ..
The UFH flow must be changed to be upstream of the 2-port CH valve, to permit independent operation.
Can the UFH return be left as-is (commoned into the CH return) so that will be upstream of the HW cylinder return?