An underfloor heating system has three mechanical parts people think about and one electrical part almost nobody does. The pipe, the manifold and the heat source get specified carefully. The controls get wired by whoever is on site that day, and that is where a surprising share of poorly performing systems actually go wrong.
Underfloor heating controls are a chain, not a collection of parts. A room thermostat senses temperature and asks for heat. A wiring centre receives that request, powers the right actuator, and tells the heat source and pump to run. The actuator opens a valve on the manifold so water reaches that one loop. Break any link and the symptom looks identical: a floor that will not heat, or one that will not stop.
This article follows the chain from the wall to the manifold, explains what the wiring centre does that nothing else can, and sets out the mistakes that cause most control faults.
The Control Chain, End to End
Four stages, in order.
1. The room thermostat measures air temperature, compares it with setpoint, and closes a contact when heat is needed.
2. The wiring centre, also called the base station or wiring manifold, is the junction between the control side and the power side. It takes the thermostat signal, supplies voltage to the correct actuator, and issues a demand signal to the heat source and the circulator.
3. The thermal actuator sits on a valve insert on the manifold return bar. Powered, it opens; unpowered, it closes. One actuator per circuit.
4. The heat source and pump respond to the wiring centre’s demand output rather than to the thermostat directly.
That fourth point is where most of the confusion lives, so it gets its own section below.
Thermostat Types, and Why They Must Match the Wiring Centre
This is the single most common specification error, and it is avoidable in thirty seconds of checking.
There are three electrical arrangements, and they are not interchangeable:
- Volt-free, also called dry contact. The thermostat simply closes a switch. It supplies no power of its own. The wiring centre senses the closed contact.
- Switched live. The thermostat outputs mains voltage when calling for heat. The wiring centre expects to receive that voltage on its zone input.
- Low voltage, typically 24 V. Used in systems designed around a 24 V actuator and control bus.
Mix them up and the outcomes differ. A volt-free thermostat wired into a terminal expecting switched live produces nothing at all, and the installer concludes the thermostat is faulty. Feeding mains into an input designed for a dry contact can damage the board. Neither failure announces itself clearly.
Check the wiring centre’s input type first, then choose thermostats to match. Not the other way round.
Beyond the electrical arrangement, the practical choices are wired against wireless, and whether a floor sensor is used.
Wireless thermostats pair to a receiver at the wiring centre, with battery life typically one to two years. They earn their place on retrofit work, where chasing cable to each room means lifting finishes. On new build, wired is simpler and has nothing to go flat.
Floor sensors matter more than people expect. An air sensor alone cannot protect a floor covering from overheating, and timber, vinyl and engineered boards usually carry a surface temperature limit around 27 °C. A thermostat with a floor sensor can enforce that limit directly. It is also a failure point: a sensor reading open or short circuit will make many thermostats refuse to call for heat at all, often with no useful indication of why. Our note on underfloor heating sensors covers the resistance values and how they are read.
For the device side in more depth, see underfloor heating thermostats, types and failures and programmable room thermostats.
What the Wiring Centre Actually Does
A wiring centre looks like a terminal block in a box, which undersells it considerably. It performs five distinct jobs.
Zone termination. Each zone’s thermostat and its actuator or actuators land on one channel, so the wiring is organised by room rather than by a bundle of cables meeting at the manifold.
Actuator supply. It provides the switched voltage the actuator needs, 230 V or 24 V depending on the system.
Boiler or heat pump demand, via the end switch. Covered in its own section below, because this is the one that gets missed.
Pump control. A dedicated pump output, usually with a short start delay so the pump holds off for two or three minutes while the actuators open. Without that delay the pump runs briefly against closed valves every cycle.
Pump overrun. After the last zone closes, the pump continues for a few minutes to dissipate residual heat from the heat exchanger rather than letting it sit.
Our base station range covers these functions across different zone counts.
The End Switch: The Part That Gets Missed
If you take one thing from this article, take this.
The wiring centre provides a volt-free end switch output. It closes when any zone calls for heat and opens when the last zone is satisfied. That output connects to the heat source’s demand or room stat terminals, and it is what tells the boiler or heat pump to fire.
Leave it unconnected and you get one of two outcomes, both common and both easy to misdiagnose:
The heat source runs continuously. If its own internal control is set to run on a timer or permanently, it heats water regardless of whether any floor zone wants it. The house may stay warm, so nobody reports a fault, and the energy bill carries the cost quietly for years.
The heat source never fires. If it is waiting for a demand signal that never arrives, the actuators open, the pump runs, and cool water circulates. The floors stay lukewarm and the obvious suspects, pump and actuators, all test fine.
That second case is worth remembering, because the symptom points away from the actual fault. Everything in the manifold cabinet is working exactly as designed. One missing wire is the whole problem.
Normally Closed or Normally Open Actuators
Thermal actuators come in two configurations and the choice is a design decision, not a preference.
Normally closed, or NC, is the default and the right answer in almost all heating applications. No power means the valve is shut. If the controls fail or power is lost, the floor stops heating. That is the safe failure direction: a cold room is an inconvenience, an uncontrolled hot floor can damage a floor covering.
Normally open, or NO, means no power equals open valve. It is used where failing to heat is the worse outcome, and in some cooling arrangements.
Both are driven by a wax thermostatic element that expands when heated by a small internal resistor. That mechanism explains their behaviour: actuation takes three to five minutes in each direction, and holding power is low, typically around 1 to 2 W. They are not fast and they are not meant to be. A floor has hours of thermal lag, so a valve that takes four minutes to open changes nothing.
Do not judge an actuator in thirty seconds. Our guide to thermal actuator working principles explains the wax mechanism, and thermal actuator types covers the variants.
The First-Open Function, and the Trap In It
Most actuators ship with a first-open or manual-open feature. A small retaining clip holds the valve open out of the box, so the system can be filled, purged, pressure tested and the screed dried before any controls are wired.
Once the actuator is first powered, the wax element expands and the clip releases, and from then on the actuator behaves normally.
The trap: if the actuators are never powered, they stay open forever. The floor heats, every room gets water, and the system appears to work. But there is no zone control at all. Every room runs whenever the heat source runs, and nobody notices because nothing is cold. We have seen installations run for years in this state, with the owner wondering why their zoning does nothing.
After commissioning, confirm each zone actually closes. Turn one thermostat well below room temperature and check that circuit’s flow meter drops to zero within five minutes.
Zone Wiring and Channel Limits
One thermostat defines a zone. A zone can contain more than one loop.
A large room served by two or three loops needs an actuator on each, all wired to the same wiring centre channel so they operate together. That is normal and correct.
What is not correct is ignoring the channel limit. Each wiring centre states a maximum number of actuators per channel, commonly three or four, set by the combined holding current and the inrush when they are first energised. Exceed it and the symptoms are intermittent: actuators that open sluggishly, or one that does not open when the others do, or a relay that fails after a season. Count the actuators per channel against the rating before wiring, not after a complaint.
The layout decision upstream matters too. One loop per room wherever room size allows gives clean zone control; a loop that crosses two rooms cannot be zoned separately whatever the controls do. Our guide to underfloor heating pipe layout covers that side, and the manifold specifications page gives the port and actuator spacing figures.
Protecting the Pump When Every Zone Closes
When all rooms reach setpoint, every actuator shuts. If the circulator keeps running against a closed manifold, it has nowhere to push water. The result is noise, wasted electricity and shortened pump life.
Two accepted solutions:
- Pump shutdown through the end switch. Once the last zone closes, the wiring centre drops the pump. Cleaner, and it saves energy.
- Differential pressure bypass. A spring-loaded valve across flow and return opens above a set pressure. Simple, but it recirculates water for no benefit.
What you must not do is wire the pump to a permanent live. It is a common retrofit shortcut and it guarantees the pump runs against closed valves every time the house is warm.
Control Strategy: Why Setback Works Differently Here
Underfloor heating has high thermal mass, and that changes how it should be scheduled.
A radiator system responds in minutes, so a deep night setback of four or five degrees followed by a fast morning recovery works well. A screed floor takes hours to respond. Drop it five degrees overnight and the morning recovery runs the heat source at high output into a cold slab, often for longer and at a higher flow temperature than simply holding the setpoint would have required. On a heat pump, where efficiency falls as flow temperature rises, deep setback can cost more than it saves.
The approach that suits underfloor heating is a shallow setback, one to two degrees, held for longer, or no setback at all with weather compensation doing the work.
Weather compensation uses an outdoor sensor to shift the flow temperature with outdoor conditions, so the floor delivers slightly more or less output continuously rather than cycling. For a high mass emitter this is the better control philosophy, and on a heat pump it is where the efficiency gains are. Our note on room thermostat settings covers the practical side.
Seven Wiring Mistakes That Cause Most Control Faults
In rough order of how often we see them:
- Thermostat type mismatched to the wiring centre input. Volt-free into a switched live terminal, or the reverse. Produces a dead zone that tests as a faulty thermostat.
- End switch not connected. Heat source either runs permanently or never fires. The manifold tests perfect.
- Actuators left in first-open. System heats, zone control does nothing, nobody notices.
- Pump on permanent live rather than through the wiring centre. Runs against closed valves.
- Too many actuators on one channel. Intermittent opening, premature relay failure.
- NO actuators fitted where NC was designed. Zones permanently open, and the fault direction is backwards on power loss.
- Floor sensor fitted but not enabled in the thermostat, or enabled without the sensor connected. Either the floor limit is not enforced, or the thermostat refuses to call at all.
None of these require new hardware. All of them are an hour with a meter and the wiring diagram.
Commissioning Checklist
Work through this after wiring and before handover. It takes twenty minutes and it catches all seven faults above.
- Set every thermostat well above room temperature. Confirm each channel LED lights on the wiring centre.
- Confirm supply voltage at each actuator’s terminals while its zone is calling.
- Wait five minutes, then confirm each circuit’s flow meter shows flow.
- Confirm the end switch has closed and the heat source has fired.
- Set every thermostat well below room temperature. Confirm all flow meters drop to zero and the pump stops, or that the bypass is operating as designed.
- Test one zone in isolation: that circuit flows, every other circuit reads zero. This is what proves zoning actually works.
- Check the floor sensor reading against its temperature curve if one is fitted.
- Record the flow meter settings on a label inside the manifold cabinet, with the date.
That last item costs nothing and saves an hour on every future service visit. If anything behaves oddly during this sequence, air in the loops is a common culprit rather than a control fault: see how to bleed underfloor heating.
Legom Underfloor Heating Controls
Jiaxing Legom Technology Co., Ltd. manufactures the full control chain from our facility in Jiaxing, Zhejiang, supplying more than 90 countries.
That means we make every link described above rather than integrating other people’s parts: room thermostats in wired and wireless versions, base stations and wiring centres with end switch and pump outputs, thermal actuators in normally closed and normally open variants at 230 V and 24 V, and the wax thermostatic elements inside them.
Making the elements ourselves is what lets us hold actuation timing consistent across a production run, which matters when a distributor supplies spares into an installed base rather than one-off units.
On the hydraulic side we manufacture manifolds in stainless steel and brass, oxygen barrier floor heating pipe, and the mixing valves for the blending group, so a complete system can come from one supplier with one set of documentation.
For brands specifying to their own range, our OEM and ODM service covers zone counts, voltage, terminal layout, labelling and market documentation. Tell us the destination market alongside the specification and we will confirm the approval position before quoting.
Frequently Asked Questions
What does a wiring centre do in underfloor heating?
It connects the control side to the power side. It terminates each zone’s thermostat and actuators, supplies the actuator voltage, issues a volt-free demand signal to the heat source through its end switch, and controls the pump including start delay and overrun.
What is the end switch and why does it matter?
It is a volt-free output that closes when any zone calls for heat and opens when the last zone is satisfied. It tells the boiler or heat pump to fire. Leave it unconnected and the heat source either runs permanently or never fires at all, while the manifold itself tests perfectly.
Should I use normally closed or normally open actuators?
Normally closed for almost all heating applications. No power means the valve shuts, so a control or power failure stops heat rather than leaving a floor heating uncontrolled. Normally open is for the specific cases where failing to heat is the worse outcome.
Why is my floor warm everywhere even when only one room is calling?
Most likely the actuators are still in their first-open position and were never powered, so every valve is held open. Check by turning one thermostat right down and watching that circuit’s flow meter: it should reach zero within five minutes.
How long does a thermal actuator take to open?
Three to five minutes in each direction, because a wax element has to heat and expand. That is by design. A floor has hours of thermal lag, so faster actuation would gain nothing.
How many actuators can I wire to one zone?
Check the wiring centre’s stated limit, commonly three or four per channel, set by combined holding and inrush current. Exceeding it causes intermittent opening and premature relay failure rather than an obvious fault.
Can I use a night setback on underfloor heating?
A shallow one. A screed floor takes hours to respond, so a deep setback forces a long high-output recovery that often costs more than it saves, particularly on a heat pump. One to two degrees held longer, or weather compensation with no setback, suits a high mass emitter better.
Do I need a floor sensor as well as a room thermostat?
If the floor covering has a surface temperature limit, which timber, vinyl and engineered boards usually do at around 27 °C, then yes. An air sensor alone cannot enforce it. Be aware that a sensor reading open or short circuit will stop many thermostats calling for heat at all.
“We supply the thermostat, the wiring centre and the actuator, and the fault reports we get are almost never about the parts. They are about how the three were connected. The end switch is the one that costs people real money, because a heat source with no demand signal either runs all winter for nothing or never fires while everything in the manifold cabinet tests correctly. Commission the chain, not the components, and prove that one zone can run while the others stay shut.”
— Maggie Shen, Director of Legom
Reviewed by Maggie Shen, Director at Legom, on October 11, 2026. This article was reviewed for technical accuracy, including the volt-free, switched live and 24 V thermostat arrangements, the wiring centre end switch and pump overrun functions, normally closed and normally open actuator fail directions, wax element actuation timing and holding power, the first-open commissioning trap, channel actuator limits, and the thermal mass argument against deep setback.