Multiple zone underfloor heating

11 Mar 2012
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United Kingdom
Hello All,

I am getting a new boiler fitted shortly. This will be feeding my underfloor heating system and hot water. Each room of the house (bungalow) each has it's own underfloor heating circuit and thermostat. Each thermostat is linked back to a Herz actuator on the underfloor heating manifold so as each room reaches temperature the actuator closes off the particular underfloor heating circuit.
Thus ... 240v from timeclock--------boiler, pump (undefloor), thermostats

then the 240v from the thermostats goes to the actuators

the actuators are closed when the 240v (via thermostat) switches off

The odd thing (well to me) is that when the central heating is on the main pump is never on, this only comes on with the hot water which is wired in the traditional way ---- tank stat----motorised valve-------pump,boiler

The only time the boiler is off when the central heating is on is when the temperature on it's own built-in thermostat is reached. Ideally I would like the room stats to control everything, that is switch off feed to the actuators and switch off the 240v to the pumps and boiler but as it is presently wired that can't be achieved. So, question is how best to achieve it ?


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You need some relays to prevent back-feed between circuits.

Download the Honeywell Wiring Guide Issue 16 from Here and look at the circuit diagram on page 14.
So, question is how best to achieve it ?

Herz do master/slave modular zone control units. Are these fitted and properly wired?
Norcon, the only Herz eqpt are the actuators. The stats are normal Danfoss RM230's and no other electrickery after that bar the programmer.

D_Hailsham - thanks for that bit of inspiration off to RS to buy a pile of relays now.


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You should use the herz controllers which the room stats are wired back to and should have built in time delay relays controlling primary and secondary pumps.
This is to give time for the circuit actuaters to open.

Where did you buy the manifold?

The rehau fs control unit for example delays the secondary pump for 180 seconds and the primary pump for 190 seconds.
Myson do a similar one as do Glo. Bassetts supply the Glo system but you'd need to check if they do a 240v version. Bassetts are in Omagh beside you.
Just for interest, underfloor is much better supplied by a variable temperature controlled by weather compensation. On-off control is not as good. There is always a temptation to install apparently sophisticated control such as individual actuators for every room, but overall flow temperature control is more effective.

The temperature difference between the floor and the room is much less than the difference between a radiator and the room. Any change in room temperature will vary the delta T - and therefore the output - by a proportionally greater extent and this makes it largely self-regulating.

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