Short answer: In a wired underfloor heating system, each room thermostat connects to one zone on a wiring centre. When it calls for heat, the wiring centre powers that zone's thermal actuators on the manifold, switches on the UFH pump and closes a volt-free contact that tells the boiler or heat pump to fire. A Heatmiser UH4 takes 4 zones and a UH8 takes 8, each with up to 6 actuators per zone. The wiring centre needs a 5A fused supply, and a new circuit for it is notifiable electrical work in England.
The wiring centre is the junction box of an underfloor heating system. Everything electrical meets there: thermostats, actuators, the pump and the heat source. Get the zone plan and the heat source connection right and the system runs quietly for years. Get them wrong and you get rooms that heat when they shouldn't, a pump that runs all day, or a boiler that never fires.
This guide covers how zones map to loops, what each terminal on a wiring centre does, how to connect it to different boilers and heat pumps, radiator zones, two-manifold systems and the rules on who can do the work. For choosing the thermostats themselves, see underfloor heating thermostats explained.
What is a UFH zone, and how is it different from a loop?
A zone is an area controlled by one thermostat. A loop is one length of pipe on one manifold port. One zone can have several loops, each with its own actuator, all opening together.
| Item | One per | Sets |
|---|---|---|
| Loop | Manifold port | Manifold size |
| Actuator | Loop | Actuator count |
| Thermostat | Zone | Wiring centre size |
| Wiring centre | Up to 4 or 8 zones | Heat source link |
So a 36m² kitchen-diner with three loops is one zone with three actuators. Heatmiser wiring centres allow up to 6 actuators per zone, within a 5A total board load. Our guide to how many manifold ports you need covers counting the loops.
Most systems in England have one zone per room, because the Building Regulations guidance expects room by room temperature control in most new systems. With a heat pump, fewer, larger zones often work better. See underfloor heating with a heat pump.
What does each terminal on a UFH wiring centre do?
A 230V wiring centre has four groups of terminals: thermostat inputs, actuator outputs, the pump output and the heat source contact. This is how the Heatmiser UH8 manual describes them.
| Terminals | What they carry |
|---|---|
| Thermostat L, N | 230V supply out to the thermostat |
| Thermostat S/L | Switched live back when it calls |
| Zone outputs L, N | 230V to that zone's actuators |
| Pump L, E, N | 230V to the UFH pump on demand |
| Heat enable LS, LR | Volt-free switch to the heat source |
The sequence on a call for heat is: thermostat sends a switched live, the zone LED lights, the zone output powers its actuators, the pump output switches on, and the heat enable contact closes. When no zone is calling, the pump and heat source stop. That is boiler interlock, and the wiring centre gives it to you without extra relays.
The UH8 manual specifies a 5A fused mains supply and a 5A anti-surge fuse on the board, with each relay rated 3A resistive and a 5A resistive total. Heatmiser's wiring diagrams use 1.5mm² three-core and earth and four-core and earth cable.
Which wiring centre do I need?
Choose by the number of zones and the type of thermostat. Wired 230V, wireless and 12V thermostats each need their own wiring centre.
| Wiring centre | Zones and stats | Price |
|---|---|---|
| Heatmiser UH4 | 4, wired 230V | £64 |
| Heatmiser UH8 | 8, wired 230V | £77 |
| Heatmiser UH8-RF | 8, wireless | £134 |
| Heatmiser UH8-N | 8, 12V network | £144 |
Prices inc VAT, October 2026. The UH4 can use zone 4 for a radiator circuit and has a hot water output. The UH8 and UH8-N can use zone 8 for radiators, and the UH8-RF can set any zone as a radiator zone in software.
If you have 4 zones now but might add a room, the UH8 costs only £13 more than the UH4. The UH8-N suits jobs where you want only 12V cable in the room walls, with neoStat 12V thermostats.
How do I connect the wiring centre to a boiler or heat pump?
Use the volt-free heat enable contact. Because it is a plain switch, it can call almost any heat source, as long as you wire it to the right input.
- Combi boiler: the heat enable contact connects to the boiler's external control or room thermostat terminals, following the boiler manual. The UFH pump and blending valve sit at the manifold.
- System boiler, S-plan: the UFH circuit gets its own 2-port zone valve. The wiring centre's pump/valve output powers the UFH pump and opens the valve. The valve's end switch (usually grey and orange wires) connects to the Gr and Or terminals so the boiler only fires once the valve is open.
- Y-plan with a mid-position valve: the UH8 manual says mid-position valves, or valves that need a closing signal, need a changeover relay. Many installers add a separate 2-port valve for the UFH instead.
- Heat pump: the heat enable contact goes to the heat pump's heating demand input, as set out in the heat pump installation manual. On a non-mixing set, the heat pump may also control the Grundfos UPM3 Flex pump speed by PWM.
- Wireless boiler link: with a UH8-RF, a Heatmiser RF-Switch (£50) at the boiler replaces the cable from the manifold.
Never feed mains from the wiring centre into a boiler's low-voltage control terminals. Check the heat source manual for what its demand input expects.
Can a UFH wiring centre control radiators as well?
Yes, on one zone. Set zone 8 on a UH8 to radiator mode and it will open a radiator zone valve and fire the boiler, but it will not start the UFH pump.
This suits the common layout of underfloor heating downstairs and radiators upstairs on one boiler. The radiator thermostat wires to zone 8 like any other, and its zone output drives the radiator circuit's 2-port valve. That leaves 7 zones for the underfloor heating. On a UH4, zone 4 does the same job.
If the radiators need more than one zone, use a separate programmer and zone valves for them, and keep the UFH on its own wiring centre.
What if I have two manifolds or more than 8 zones?
Use one wiring centre per manifold, mounted next to it. Each wiring centre drives its own manifold's actuators and pump, and each one's heat enable contact must be able to call the heat source.
- Split zones by manifold. A room's loops and its thermostat belong on the same manifold and wiring centre.
- Size each wiring centre to the zones on its manifold: UH4 for up to 4, UH8 for up to 8.
- Power each pump from its own wiring centre, so a pump runs only when its own manifold has demand.
- Bring both heat enable contacts to the heat source so either manifold can call for heat. Your electrician will choose how, using the heat source's wiring instructions.
- Label every zone at both wiring centres with the room name.
For app control across both floors, a single Heatmiser neoHub can run neo thermostats on both wiring centres.
Worked example: wiring schedule for a ground floor
An 8-loop ground floor with 5 rooms, plus radiators upstairs, fits one Heatmiser UH8. The schedule below is what the electrician needs on the day.
| Zone | Room and stat | Actuators |
|---|---|---|
| 1 | Kitchen-diner | 3 |
| 2 | Lounge | 2 |
| 3 | Hall | 1 |
| 4 | Utility | 1 |
| 5 | WC | 1 |
| 6, 7 | Spare | 0 |
| 8 (RAD) | Upstairs radiators | Zone valve |
Kit: UH8 (£77), 8 actuators at £12 (£96) and a 22mm 2-port zone valve for the radiator circuit (£57), so £230 inc VAT, October 2026, before thermostats. With six Heatmiser Edge thermostats at £47, the controls total £512. Two spare zones leave room for a future extension.
Do I need an electrician to wire underfloor heating?
Yes, use a qualified electrician. In England, Approved Document P says the installation of a new circuit, the replacement of a consumer unit, and any addition or alteration to circuits in a special location such as a bathroom are notifiable.
A new supply for a wiring centre is usually a new circuit or a spur from one, so it needs to be done and certified properly. The bathroom special location extends 600mm around a bath or shower tray, up to 2.25m high, which matters for thermostat and floor probe positions. A registered electrician can self-certify notifiable work. Our guide to electric UFH in bathrooms covers zones in more detail.
What you can do yourself is the planning: the zone schedule, thermostat positions and cable routes. Run thermostat cables before plastering, and fit a floor probe in conduit if the room has a timber or vinyl finish.
Products for this job
- Heatmiser UH8 8 Zone Wiring Centre
- Heatmiser UH4 4 Zone Wiring Centre
- Heatmiser UH8-RF Wireless Wiring Centre
- Heatmiser UH8-N 12V Network Wiring Centre
- 2-Wire Thermal Actuator 230V
- 2-Port Motorised Zone Valve
- Heatmiser Edge Thermostat 230V
- All wiring centres
Related guides: Underfloor heating thermostats explained, Actuator, zone valve and wiring centre faults and How many manifold ports do I need?
Plan your zones free with MaxHeatUFH ProLoop. Add your rooms and floor type, and get a loop design with zones, plus a kit list with the wiring centre, actuators and thermostats priced. Start your design
Frequently asked questions
How many actuators can one thermostat control?
On Heatmiser UH4, UH8, UH8-RF and UH8-N wiring centres, up to 6 actuators per zone, within the 5A total board load.
Do I need a wiring centre for underfloor heating?
For more than one zone, yes. It links the thermostats to the actuators and gives pump and boiler interlock. A single-zone system can sometimes be wired without one, using a thermostat that switches the pump and heat source directly.
Is the boiler connection on a UFH wiring centre live or volt-free?
On the Heatmiser UH8 it is volt-free. The LS and LR terminals act as a switch, so it can call a combi, a system boiler or a heat pump.
Can I put UFH and radiators on one wiring centre?
Yes, on one radiator zone: zone 8 on a UH8 or zone 4 on a UH4. In radiator mode that zone fires the boiler without starting the UFH pump.
Why does my UFH pump run when no room is calling?
Check that the pump is wired to the wiring centre's pump output, not a permanent live, and that no thermostat is stuck calling. A zone LED that stays lit points to the thermostat or its wiring.
What cable do UFH thermostats need?
Heatmiser's diagrams for 230V thermostats use 1.5mm² three-core and earth or four-core and earth cable back to the wiring centre. 12V neoStats on a UH8-N follow the UH8-N instructions, and wireless thermostats need no cable at all.
Where should the wiring centre go?
Next to the manifold, so actuator leads reach it, and somewhere dry with room to work. Keep it accessible for future changes and fault finding.
Sources: Heatmiser UH8 wiring centre manual, Approved Document P (2013), Approved Document L, Volume 1