Why is underfloor heating uneven and how to fix it?

How to tell if the problem is serious or common?

Before looking for causes, it's worth mapping exactly where the cold spots are and when they appear — this information will help narrow down the problem faster later on.

• Is the cold spot across the entire room or just a few square metres?
• Has the unevenness always been present, or did it appear recently, for example after maintenance or moving furniture?
• Is the problem in one specific room or several rooms at once?
• Is the difference minor (a couple of degrees) or is part of the floor noticeably cold?

Air in the heating circuits — the most common cause

Underfloor heating typically consists of several kilometres of pipe loops connected to a manifold. If air remains in a circuit during installation or subsequent water changes, warm water cannot circulate properly in that area, and the floor will be cooler in that specific region.

Air usually accumulates at the highest point of the circuit or near the manifold, causing unevenness to often appear in a specific pattern — for example, in one corner of the room where the circuit begins.

Unbalanced manifold — circuits receive unequal water flow

At the manifold, each circuit has a separate regulating valve or flow meter, which can restrict or increase the amount of water in a specific circuit. If this adjustment is done incorrectly or not at all, shorter circuits receive too much water and longer ones too little.

This results in a situation where rooms with shorter circuits (e.g., a small bathroom) are too hot, while large rooms with longer circuits only partially warm up.

• Check the manifold's flow meters (if present) — do all readings match the design values?
• If flow meters are not present, balancing requires a specialist to measure temperatures and adjust the circuits accordingly.
• Balancing should be re-done if room usage has changed, for example, if an extension was built or the layout modified.

Differences in circuit length and resistance

Each underfloor heating circuit varies in length and thus in hydraulic resistance — a longer circuit offers greater resistance to water flow, meaning it will receive less water than a shorter circuit without regulation.

This is one reason why hydraulic balancing during installation is so crucial — without it, areas with short circuits will quickly overheat, while long circuits won't receive enough hot water.

Faulty thermostat sensor and actuator

Each room or zone typically has its own thermostat, which instructs the manifold's actuator to close or open a circuit. If the thermostat sensor is incorrectly positioned (e.g., in direct sunlight or near a radiator), it will show an incorrect temperature, and the circuit will switch off too early.

Similarly, a faulty or jammed actuator may remain in the closed position, preventing that specific circuit from receiving any hot water, even if the thermostat sends the correct command.

• Check if the thermostat accurately displays the actual room temperature — compare it with a separate thermometer.
• Listen for a clicking sound from the manifold actuator when changing the temperature — this indicates the actuator is moving.
• If the actuator doesn't move or make a sound, it's likely jammed or faulty and needs replacing.

Insufficient circulation pump pressure

The circulation pump must be able to push water through all circuits, including the longest circuit with the highest resistance. If the pump is incorrectly sized, too weak, or set to too low a speed, the furthest circuits will not receive enough hot water with sufficient pressure.

This typically manifests as rooms closer to the manifold warming up properly, while the furthest rooms remain systematically cooler — not in random spots, but always in the same locations.

Inadequate insulation and subfloor

If the insulation layer beneath the underfloor heating is of uneven thickness, damaged, or completely missing in some areas, part of the heat will escape downwards or sideways instead of rising into the room — this creates localised cold spots unrelated to the pipework itself.

Similarly, the surface beneath the floor also affects the outcome — for example, if one part of the floor is situated above a cold cellar or a ventilated crawl space, and another part above a heated room, the heat loss will differ even with identical pipework.

Impact of flooring material and thickness

Different flooring materials conduct heat at different rates — ceramic tiles transfer heat quickly, while thick carpets, parquet, or certain laminates insulate and slow down heat transfer into the room.

If one room has tiles and an adjacent room has a thick carpet or wooden floor, the latter will often feel cooler, even if the pipework operates identically in both rooms — this isn't a technical fault, but a natural difference in materials.

Impact of furniture and rugs on heat distribution

Large pieces of furniture, such as low sofas or heavy wardrobes placed directly on the floor without legs, obstruct the free upward movement of heat, creating a heat-trapping zone underneath, while uncovered floor areas feel comparatively cooler.

Similarly, thick rugs and rigid underlays significantly reduce heat transfer, so when placing rugs, consider where the heating circuits are located and which areas are intended for primary heat emission.

Step-by-step check before calling a specialist

A systematic approach helps to quickly identify the root cause of the problem and provides the specialist with valuable information upon arrival.

• Inspect the manifold — are all circuits open, or are any visibly closed or partially shut?
• Feel the temperature of the pipes by hand at the manifold for each circuit — is any pipe significantly colder than the others?
• Bleed each circuit individually until the flow is smooth and quiet.
• Check thermostats and ensure they accurately display the actual room temperature.
• Monitor any gauges or indicators on the manifold, if present, and note down differences between circuits.
• Map cold areas on a plan and mark if they correspond to a specific circuit location.

When should you call a heating system specialist?

Some issues can be resolved independently, but many require measuring equipment and a specialist who understands system hydraulics.

• If bleeding doesn't improve the situation and one circuit remains cold.
• If the manifold lacks flow meters and balancing has never been done.
• If you suspect a faulty actuator or thermostat.
• If the problem appeared recently without an apparent cause, e.g., after a long shutdown in summer.
• If you suspect the circulation pump is too weak for the entire system.

How does this topic differ from underfloor heating installation?

If you are looking for information on which type of underfloor heating to choose — water or electric underfloor heating, which suits which floor covering — these topics are covered in a separate article on different types of underfloor heating and on our service page for underfloor heating installation.

This article focuses on diagnosing and rectifying uneven heating in an already operational system, not on selecting or installing a new system.

How to prevent uneven heating in the future?

Most uneven heating problems are preventable with correct installation and regular maintenance.

• Have the underfloor heating designed and installed so that circuit lengths are as similar as possible or balanced according to resistance.
• Demand hydraulic balancing from the installer before commissioning the system.
• Bleed the system at the start of the heating season, especially after a long summer shutdown.
• Order underfloor heating maintenance every couple of years to detect actuator and thermostat issues early.
• When placing large furniture and thick rugs, consider where the heating circuits are located.

Impact of heat source and mixing valve on uneven heating

The flow temperature of underfloor heating is typically regulated by a mixing valve, which blends hot water from the heat source (heat pump, gas boiler, district heating) with return water to achieve the appropriate floor temperature, usually 30–45 degrees Celsius. If the mixing valve's sensor or valve malfunctions, the water reaching the manifold may have an unstable temperature, affecting all circuits simultaneously.

In such cases, the problem isn't necessarily in one specific room, but the entire house's underfloor heating feels alternately warmer or colder, depending on how the mixing valve is currently regulating. If you notice that the unevenness varies daily or even hourly, it's worth checking the mixing valve and its sensor, rather than just the manifold.

• Check if the mixing valve's flow temperature remains stable by measuring it at different times of day.
• If you use a heat pump, ensure it can provide a sufficient water volume to all zones simultaneously, especially in cold weather.
• For gas boilers or district heating, check that the heating control automation is working correctly and the flow temperature doesn't fluctuate excessively.

Varying room heating needs and thermostat settings

Each room has different heating requirements depending on its size, number of windows, cardinal direction, and purpose. If all rooms are set to the same target temperature, a north-facing room or one with many windows may systematically remain cooler, even if the system is otherwise fine; it simply requires a higher set temperature or longer operating time.

Similarly, whether thermostats are integrated into a unified zone automation system or each room operates independently affects the outcome — in an uncoordinated system, the warm and cold cycles of neighbouring rooms can create the impression of a technical fault, when in reality, the settings just need to be adjusted on a room-by-room basis.

Impact of seasonal weather conditions on perceived unevenness

Uneven heating may feel more pronounced in spring and autumn than in mid-winter because the system operates at lower power, and smaller differences between circuits become more noticeable. In mid-winter, when the entire system operates under higher load, the same unevenness may be less apparent because all circuits receive more hot water.

This means if you notice the problem specifically during transitional periods, it might not indicate a new fault, but rather that existing, previously hidden imbalance becomes more visible under lower load. This information should be passed to a specialist as it helps to pinpoint the problem faster.

What role does regular maintenance play in preventing unevenness?

Unlike traditional radiator heating, underfloor heating is hidden within a concrete slab or layer, limiting physical access to the pipework. Problems aren't visible to the eye — all information comes from the manifold, thermostats, and temperature differences. This makes regular maintenance particularly important, as small deviations are easier to spot before they grow into noticeable unevenness.

Initial values measured and recorded during maintenance — such as the flow rate and temperature of each circuit — provide a basis for later comparison. If, after a year, some circuit readings have significantly changed, the problem can be identified before it affects comfort or creates visible cold spots on the floor.

Many problems discussed above — slight air accumulation, minor shifts in balance, early actuator wear — develop slowly over months. This is why an annual inspection before the heating season begins is one of the most effective ways to keep the system working evenly and avoid major repairs in the future.

• Have the manifold and circuit settings checked before each heating season, especially if the system was shut down for a long period in summer.
• Keep a record of the measured values for each circuit so that changes over time can be compared during subsequent checks.
• If you notice small but persistent unevenness, don't wait for it to become pronounced — early intervention is usually cheaper and faster.

Specifics of uneven underfloor heating in apartment buildings

In apartments where underfloor heating is connected to a communal heating unit, the pressure and temperature available to an individual apartment's manifold depend on the overall balance of the building's system — if neighbouring apartments consume a lot of hot water or heating water simultaneously, this can temporarily affect the underfloor heating pressure in other apartments.

In such a situation, it's worth first clarifying whether the unevenness occurs only in your apartment or if neighbours also report a similar problem — in the latter case, it's likely a building-level balancing issue, which requires resolution through a specialist commissioned by the apartment association or building manager, rather than just adjusting an individual apartment's manifold.