How Underfloor Heating Controls Actually Work
Understanding the chain makes every symptom on this page easier to place. In a typical wet underfloor system it goes like this: the room thermostat decides the room needs heat, and sends a demand to a wiring centre, usually mounted near the manifold. The wiring centre does two things with that demand. It powers the actuator sitting on that room's port on the manifold, which opens the valve and lets warm water into that loop. It also sends a call for heat to the boiler and the pump, so there is hot water to circulate in the first place.
If any link in that chain is broken, the floor stays cold, and the symptom often looks identical from the thermostat. That is why controls faults get misdiagnosed so often.
Common Control Faults and What They Mean
The thermostat is calling for heat but nothing happens
The demand is being made but something downstream is not acting on it. This is the single most common underfloor heating complaint.
- Most likely cause
- The actuator on that room's manifold port is not opening, either because it has failed, seized, or is not being powered.
- Also possible
- The wiring centre is not passing the demand on, or the boiler is not receiving a call for heat at all, in which case there is no hot water to circulate.
- Worth knowing
- Thermal actuators take three to five minutes to open. Give it that long before deciding nothing is happening.
- What the fix involves
- Testing whether the actuator is receiving power and whether it physically opens, then replacing the actuator or correcting the wiring centre fault behind it.
The thermostat screen is blank or completely dead
No display means no demand can be sent, so the whole zone stays cold regardless of what the rest of the system is doing.
- Most likely cause
- Flat batteries in a wireless stat, or a lost supply to a wired one.
- Also possible
- A blown fuse in the wiring centre or at the fused spur feeding it, which often takes several thermostats out at once.
- Tell-tale sign
- If every thermostat in the house is dead, suspect the supply or the fuse rather than the stats themselves.
- What the fix involves
- Batteries first. Beyond that, finding why the supply has been lost and correcting it, then replacing the thermostat only if it has genuinely failed.
A wireless thermostat has stopped talking to the system
The stat looks alive and responds to being turned up, but the floor never reacts, because the signal is not reaching the receiver.
- Most likely cause
- The pairing between the thermostat and its receiver has been lost, very often after a power cut or a battery change.
- Also possible
- The receiver has failed, or something has changed in the building that is now blocking the signal.
- What the fix involves
- Re-pairing the thermostat to its channel on the receiver, and confirming that the channel it is paired to actually drives the right room.
One room is always too hot, or never reaches temperature
The system responds, but that particular room settles at the wrong temperature no matter what the thermostat is set to.
- Most likely cause
- The thermostat is reading the wrong temperature because of where it is mounted: in a draught, in direct sun, on an outside wall, or above another heat source.
- Also possible
- A floor sensor limit set too low, which caps the floor temperature before the room ever gets to its target.
- Also possible
- The stat is connected to a different loop than the one heating that room, which is a wiring fault rather than a control fault.
- What the fix involves
- Checking what the stat is actually sensing, correcting sensor limits, and where necessary relocating the thermostat.
The floor heats up when nobody has asked for it
Rooms get warm with every thermostat turned down, or the floor is warm in summer.
- Most likely cause
- An actuator stuck open. New actuators are often supplied held open so the system can be filled and flushed, and that first-open pin sometimes never gets released at commissioning.
- Also possible
- Crossed wiring, so a demand from one room opens the wrong port, or a wiring centre relay that has stuck.
- Also possible
- Warm water drifting into the loops from the rest of the heating system when there is no proper isolation.
- What the fix involves
- Identifying which port is passing water, replacing or resetting the actuator, and correcting the wiring behind it.
The controls are old and parts are no longer available
Nothing is dramatically broken, but a failed thermostat can no longer be replaced like for like and the system is becoming unsupportable.
- Most likely cause
- The control range has been discontinued. Wiring centres and thermostats from the 2000s and early 2010s are increasingly at this point.
- Good news
- The expensive part of your system, the pipework in the floor and the manifold, is unaffected and stays where it is.
- What the fix involves
- Replacing the control layer only, which is described in the next section.
Replacing Underfloor Heating Controls
Replacing controls is one of the least disruptive jobs on an underfloor system, because the floor never gets touched. In most homes it means new room thermostats, often a new wiring centre, and sometimes new actuators. The manifold, the loops and the screed all stay exactly as they are.
There are two things that have to match, and getting them wrong is the usual cause of a controls upgrade going badly. The first is voltage: underfloor systems run either 230V or 24V control circuits, and thermostats, wiring centre and actuators all have to be on the same one. The second is the actuator connection itself, which needs to suit the valve bodies already on your manifold rather than being assumed.
Beyond that, an upgrade is a good moment to fix things that were never right in the first place, such as a thermostat in a poor location, a room sharing a stat with a room it has nothing in common with, or a system with no proper scheduling.
Smart Controls and Underfloor Heating
Underfloor heating gains more from good controls than radiators do, precisely because it reacts so slowly. A system that knows when you actually want the room warm, and starts early enough to get there, is far more comfortable than one being turned up and down in frustration.
We work with the main control systems you are likely to already have or want, including Heatmiser, Nest, Hive, Honeywell and the control ranges supplied with Polypipe, Wunda and Nu-Heat manifolds. Which one suits you depends on what is already installed and how you want to use it, rather than on any brand being universally best.
Where it makes sense we also set up load or weather compensation, which lets the boiler run at a lower flow temperature for longer instead of cycling. That suits underfloor heating particularly well. There is more detail on our advanced heating controls page.
Related Faults
If the thermostat is definitely calling and the actuator is definitely opening, the problem is probably not in the controls. Try wiring and wiring centre faults if the boiler never fires, or cold spots and flow problems if the heat is reaching some rooms but not others.
Controls Fault FAQs
Why is my underfloor heating thermostat not turning the heating on?
Either the thermostat is not sending a demand, or the demand is not being acted on. Check the set temperature is above the room temperature and that the stat shows a heating symbol. If it is calling, the fault is downstream: the actuator on the manifold may not be opening, the wiring centre may not be passing the signal on, or the boiler may not be receiving the demand.
How long does an underfloor heating actuator take to open?
Most underfloor heating actuators are thermal rather than motorised, so they warm a wax capsule to open. They typically take around three to five minutes from the thermostat calling to the valve being fully open. Nothing appears to happen in that time, which is normal and often mistaken for a fault.
Can I fit a smart thermostat to underfloor heating?
Usually yes. Most underfloor heating can be upgraded to smart controls without changing the manifold or the pipework, provided the new thermostats match the voltage of the wiring centre and the actuators. Underfloor heating benefits more than radiators do from good scheduling, because it responds so slowly.
Do I need a new manifold to upgrade my underfloor heating controls?
Almost never. The manifold, loops and pipework normally stay exactly as they are. A controls upgrade generally means new thermostats, sometimes a new wiring centre, and occasionally new actuators if the voltage or thread does not match.
Why does one room never reach the temperature on the thermostat?
Often the thermostat itself is the problem rather than the heating. A stat mounted in a draught, in direct sunlight, above a radiator or on an outside wall reads the wrong temperature and behaves accordingly. Floor sensor limits set too low will also stop a room reaching its target.
My underfloor heating controls are obsolete. What are the options?
Older wiring centres and thermostats do reach the point where spares are no longer made. In most cases the sensible route is to replace the control layer only, keeping the manifold and pipework, which brings the system up to date and back under warranty without any disruption to the floor.