Underfloor Heating Sensors for Heat Pump Systems Explained
Last Updated: November 13, 2026
Quick Summary
Underfloor heating sensors tell a heat pump how hot to run its flow water, so they control how much electricity the system uses. Outdoor, flow, return and room sensors each feed the controller, and a weather compensation curve sets flow temperature from outdoor conditions. Keeping sensors accurately placed and the curve correctly set is what keeps running costs low.
Underfloor systems run at lower water temperatures than radiators, which helps the heat pump stay efficient.
The outdoor sensor should sit on a north-facing wall, away from direct sun.
Lowering flow temperature without checking loop balance can leave one room cold.
Adjust the heating curve in small steps of one or two degrees and recheck over several days.
Place the room sensor on an internal wall, away from radiators, draughts and direct sunlight.
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Table of Contents
How Sensors Shape Heat Pump Efficiency Under Underfloor Heating
The Sensors Your Underfloor Heating and Heat Pump System Uses
Heat Pump Weather Compensation and How It Uses Outdoor Sensing
Underfloor Heating Floor Temperature Sensor Setup and Calibration
Troubleshooting Common Sensor Errors and Next Steps With Heatgeek Wales
How Sensors Shape Heat Pump Efficiency Under Underfloor Heating
Underfloor heating sensors decide how hard your heat pump works, and therefore how much it costs to run. A small error in how the sensors talk to the controller can waste energy.
Underfloor heating is a natural partner for a heat pump. It runs at lower water temperatures than a radiator system, which helps the heat pump stay efficient.
Sensors do three main jobs:
Measure outdoor conditions so the system canpre-adjust before the house cools
Measure flow and return water so the heat pump runs at the right temperature
Measure room or floor temperature so the system stops heating once the target is reached
When one of these readings is wrong, the heat pump often overcompensates. It runs hotter than needed, which uses more electricity and shortens the time between cycles.
The Sensors Your Underfloor Heating and Heat Pump System Uses
Most underfloor heating systems with a heat pump use a few standard sensors.
Outdoor temperature sensor: Usually mounted on a north-facing wall, away from direct sun. It tells the heat pump how cold it is outside.
Flow and return sensors: These sit on the water pipes.
Floor temperature sensor: Some systems place a probe in the screed to limit how hot the floor gets.
Room thermostat or sensor: This reads the air temperature inside the room the system is controlling.
Each sensor sends its reading to the controller, which uses the numbers to set the flow temperature.
Heat Pump Weather Compensation and How It Uses Outdoor Sensing
Weather compensation is a control method that changes the flow temperature based on the outdoor temperature. As it gets colder outside, the heat pump raises the flow temperature a little. As it warms up, it lowers the flow temperature. The relationship between the two is the heating curve, and the outdoor sensor is the input that drives it.
How the heating curve works
The curve is a line on a graph: outdoor temperature along one axis, flow temperature along the other. At the design outdoor temperature for the property, the coldest day the system is sized for, the curve calls for the design flow temperature.
The slope of that line is what matters. A steep curve raises flow temperature quickly as it gets colder; a shallow curve keeps flow temperature low across a wider band of outdoor conditions.
What the curve looks like for underfloor loops
Underfloor heating changes the shape of the curve because the emitter has a large surface area and runs at low water temperatures. Underfloor systems are generally designed around lower flow temperatures than radiator systems. That means the underfloor curve is shallower and sits lower on the graph across the whole outdoor range.
An underfloor system often runs at comparatively low flow temperatures for much of the year.
Why the curve is often misconfigured
A common pattern is a curve left at the factory default, which is usually set for a generic radiator system and therefore too steep for underfloor loops. The house then runs warm on mild days, the heat pump cycles more than it should, and efficiency drops.
Watch out: raising the curve to fix a cold room masks the real problem, usually a loop balancing issue, a floor covering with high resistance, or a sensor in the wrong place, and leaves the system running hotter than the building needs for the rest of the season.
Reading the curve against real conditions
A useful check is to log outdoor temperature and flow temperature over a week and compare the actual pairs against the curve the controller is applying. If the flow temperature sits above the curve for the outdoor conditions, the curve is too steep or an offset is pushing it up. If rooms are slow to reach temperature on cold mornings, the cold end of the curve may be too low for the building's heat loss. Adjust in small steps, one or two degrees at the design point, and recheck over several days before changing anything else.
Setting the Heat Pump Flow Temperature for Underfloor Loops
The flow temperature is the water temperature leaving the heat pump for the underfloor loops. Underfloor heating works well at lower flow temperatures than radiators, which is one reason the pairing suits heat pumps. Getting the flow temperature right is the single biggest lever on running efficiency, because a lower flow temperature lets the compressor work less hard for each unit of heat delivered.
Start from the design figures
Check the design flow temperature in the system documents or on the controller. Our step-by-step guide to setting flow temperature shows how to adjust it safely from there. The design flow temperature depends on the specific system and property. If the documents are missing, the loop design, pipe spacing, screed depth and floor covering, gives a good indication of what the system can deliver at a given flow temperature.
Set the curve, not just a fixed temperature
A fixed flow temperature wastes energy on mild days. For a wider look at controls, read how to choose heat pump controls for underfloor heating. Set the weather compensation curve so the flow temperature tracks outdoor conditions, with the design flow temperature at the cold end and a low limit at the mild end. For underfloor loops the curve should be shallower than the radiator default, as covered above.
Tune over a full range of outdoor temperatures
Run the system for several days through a range of outdoor temperatures with the initial curve.
Note whether rooms hold their target on the coldest day and whether they overheat on mild days.
Adjust the cold end of the curve first, one or two degrees at the design point, if the house is slow to warm on cold mornings.
Adjust the mild end or offset if rooms overheat when it is mild outside.
Recheck over several days before making further changes.
Seasonal adjustment protocol
The first cold snap of the season is the best time to fine-tune. Run the system for a week, log outdoor and flow temperatures, and compare rooms against their targets. Make one small change at a time, note the date and the change, and leave at least three days before the next adjustment so the building and screed can respond. Keep a simple log through the season; patterns emerge quickly, and the same adjustments usually recur each year.
What lower flow temperature actually buys you
A lower flow temperature can give a steadier, more comfortable room, even though the heat pump runs for longer. The efficiency gain shows up as a lower electricity input for the same heat output, the compressor does less work per kilowatt-hour of heat delivered. The exact gain depends on the heat pump, the outdoor temperature and the emitter, so treat any figure as indicative rather than a guarantee.
Interaction with room controls
Room thermostats and zoning should sit on top of a correctly set curve, not replace it. If a room thermostat is constantly calling for heat while the curve is too low, the system will run at full output and lose the efficiency benefit. Set the curve first, balance the loops, then use room controls for comfort trimming rather than as the primary temperature control.
Watch out: lowering the flow temperature without checking loop balancing can leave one room cold while the rest of the house is comfortable, fix the balance before chasing further efficiency.
Underfloor Heating Floor Temperature Sensor Setup and Calibration
A floor temperature sensor protects the floor and tells the system when to stop heating the screed. Setup has to be done carefully.
Place the probe correctly: Fit it in the sensor pipe as the manufacturer directs, away from the heating loops.
Set the maximum floor temperature: Use the limit recommended for your floor covering. Floor coverings differ in how much heat they tolerate.
Check the reading: Compare the sensor reading with a handheld thermometer at the floor surface.
Test the cut-off: Make sure the system reduces output when the limit is reached.
Calibration is worth checking after the first few weeks, when the screed has settled and the system has run through a full cycle. If the reading is well off, the sensor may be damaged or fitted in the wrong place.
Heat Pump Room Sensor Placement and Thermostat Interaction
The room sensor tells the controller how warm the house feels. Where it sits matters a great deal.
Place the room sensor on an internal wall, away from:
Direct sunlight
Radiators, fireplaces and cookers
Draughts from doors and windows
Exterior walls
A sensor in the wrong spot causes the system to heat the wrong room or switch off too early. A room may feel cold even though the thermostat shows the set temperature when the sensor is picking up heat from a nearby source.
Troubleshooting Common Sensor Errors and Next Steps With Heatgeek Wales
Most sensor problems show up as odd readings, rooms that will not warm up, or a heat pump that runs constantly. Check these first:
Error code on the controller: Note the code and check the sensor it refers to.
Loose or damaged wiring: Look for cuts, corrosion or loose connections at the sensor.
Sensor in the wrong place: A sun-exposed outdoor sensor or a draughty room sensor will cause poor readings.
Curve set too high or too low: An unsuitable weather compensation curve can look like a sensor fault.
Some faults need a qualified engineer. Between visits, a UK homeowner maintenance checklist helps keep sensors and the system reliable. If a sensor reads wildly, the error code persists after checking the wiring, or the rooms stay cold despite correct settings, book a visit from a trained installer.
Once the faults are fixed, commission the heat pump to confirm everything works together. Our homeowner checklist for commissioning a heat pump walks through each step. You can also find local MCS-certified heat pump installers near you.
Frequently Asked Questions
Do heat pumps need room thermostats with underfloor heating?
A room thermostat is not always required, but it is useful for underfloor heating paired with a heat pump. Underfloor loops respond slowly, so a room sensor lets the controller judge how warm the space actually is rather than relying only on the flow temperature. Where a home has several zones, a thermostat per zone gives better control. Your installer can confirm which arrangement suits your building and controls.
What sensors are used with underfloor heating and heat pumps?
A typical system uses an outdoor temperature sensor for weather compensation, a flow and return sensor on the heat pump, a room sensor or thermostat, and sometimes a floor temperature sensor in the screed. Each sensor gives the controller a different piece of information about heat demand. Together they let the heat pump run at the lowest flow temperature that still keeps the home comfortable, which supports efficient operation.
Should underfloor heating use a floor temperature sensor?
A floor sensor is useful as a safety and comfort limit, because it stops the screed overheating and keeps surface temperatures within a comfortable range. It is less useful as the primary control input, since floor temperature responds slowly to changes in demand. Many installers use the floor sensor as a cut-out and rely on room and outdoor sensing for regulation. Check the controls specification for your system before deciding.
Where should a room sensor be placed for underfloor heating?
Place the room sensor on an internal wall, away from direct sunlight, radiators, the heat pump, doors to the outside and draughts. About 1.5 metres above the floor is a common height. A sensor in a representative room, such as a living room, usually gives a fair reading of the home. Poor placement is one of the most common reasons for a system that feels too hot or too cold.
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