Boilers & Pump
UFH Manifold Set (underfloor heating)
In short
Underfloor heating (UFH) warms a room through pipes laid in its floor. Its terminals: L, N, E, SL, ZL, ZN, AL, AN, LS, LR.
If this is your home: this page is written for heating engineers, and for learners under the supervision of one. It explains how the wiring works; it is not training to do the work. In England and Wales, electrical work in a home must meet the Building Regulations (Part P), and some of it must be notified to building control or done by a registered electrician; Scotland and Northern Ireland have their own rules. For the wiring, call a registered electrician or a heating engineer competent in controls. Work inside a gas boiler is for a Gas Safe registered engineer only. If you smell gas, leave the building and call the gas emergency number: 0800 111 999 in Great Britain, 0800 002 001 in Northern Ireland.
What it is
UNDERFLOOR HEATING (UFH) warms a room through pipes laid in its floor. This part is an underfloor heating MANIFOLD, with its own WIRING CENTRE: the box that controls it. It is DrawWarm's own design, wired the way the makers' UFH wiring centres are.
On the manifold:
- Flow meters on the flow rail.
- White thermal ACTUATORS on the return rail. They open the floor's pipe loops.
- A BLENDING VALVE, which keeps the floor's water cooler than the boiler's.
- The set's own PUMP.
The box controls one ZONE. When the zone's room thermostat (stat) calls, the box feeds the actuators.
Only when they are fully open does the box run its pump and close its HEAT SOURCE contact, Ls to Lr. So the boiler never fires into a shut manifold.
A maker's wiring centre closes that contact on the demand. This box always waits.
Product and brand names belong to their owners; DrawWarm is not affiliated with any manufacturer.
Terminals
| Terminal | What it is for |
|---|---|
| L | POWER L: the live (L) in, from the system's spur. So the spur stays one POINT OF ISOLATION for the whole system. |
| N | POWER N: the neutral (N) in. |
| E | POWER earth (E). The box is CLASS I: its safety relies on the earth, so it must be earthed. |
| SL | ZONE 1 SL: the switched live (SL) back from the call of the room thermostat (stat). With a live here, and L and N on POWER, the zone calls. |
| ZL | ZONE 1 L (printed L): a live out, to feed the room thermostat. It is joined inside to POWER L. |
| ZN | ZONE 1 N (printed N): a neutral out, for the room thermostat. It is joined inside to POWER N. |
| AL | ACTUATORS L (printed L): the actuators' live. Here they come wired. It is live while the zone calls: 230 volts (230 V) across AL and AN is the test. |
| AN | ACTUATORS N (printed N): the actuators' neutral, each actuator's other core. Here they come wired. It is joined inside to POWER N. |
| LS | HEAT SOURCE Ls, the live supply. It is VOLT-FREE: nothing inside feeds it. Link it from L to give a switched live to a heat-only or a system boiler. For a combi, Ls and Lr go to the boiler's own pair of terminals, as its manual says. |
| LR | HEAT SOURCE Lr, the live return: the switched live to the boiler. It goes to the boiler's SL, or to wiring centre block 10 with the radiator valve's orange. It is joined to Ls once the zone calls AND the actuators are fully open. |
What the meter reads
Live tests. On site, any reading taken with the supply on is work on or near live parts. Regulation 14 of the Electricity at Work Regulations 1989 allows it only when working dead is unreasonable, as when a fault shows only while the controls work, and only with suitable precautions: test leads made to the HSE’s guidance note GS38, fingers behind the guards. Regulation 16 allows it only for a competent person, or a learner under the supervision of one. Wiring and repairs are always done dead. In the simulator, nothing is live.
Live (L) and neutral (N) on POWER: the POWER light shows.
The room thermostat (stat) calls, putting a live on the box's switched live (SL): the ZONE 1 light shows. AL goes live at once, with 230 volts (230 V) across AL and AN, and the actuators start to open.
Fully open, after 8 seconds here: the PUMP and BOILER lights show. The pump runs, and Ls joins Lr. With Ls linked from L, Lr is live and the boiler fires.
The call ends: Lr and the pump stop at once. AL goes dead, and the actuators close over the same 8 seconds.
No link on Ls: the box asks for heat, and the BOILER light shows. But Lr stays dead, and the boiler never fires.
The heating water: the floor takes heat only while the actuators are open and the set's pump runs. With every actuator shut and no other way open, a boiler's water has nowhere to go.
Dead, across AL and AN the meter reads the six actuator heads together: about 3 kilohms in this simulator.
Where it connects
Lessons that use it
- Underfloor heating on its own
Intermediate · Underfloor and mixed systems
- Underfloor downstairs, radiators upstairs
Intermediate · Underfloor and mixed systems
Practise it in the simulator.
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