Why does the whole underfloor heating system heat unevenly?

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 to pinpoint the problem faster later on.

• Is the cold spot across the entire room or just a few square metres?
• Has the unevenness always been there, or did it appear recently, for example, after maintenance or rearranging furniture?
• Is the problem in one specific room or several rooms at once?
• Is the difference small (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 remain cooler precisely in that region.

Air mostly accumulates at the highest point of the circuit or near the manifold, which is why unevenness often occurs 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.

The result is a situation where rooms with shorter circuits (e.g., a small bathroom) are too hot, while larger rooms with longer circuits only partially heat up.

• Check the manifold's flow meters (if present) — do all readings match the designed values?
• If there are no flow meters, a specialist must be called for balancing, who will measure temperatures and adjust the circuits accordingly.
• Balancing should be repeated if room usage has changed, for example, if a room was added or the layout was altered.

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 less water will pass through it than a short circuit without regulation.

This is one reason why hydraulic balancing during installation is so important — without it, areas with shorter circuits quickly overheat, while longer circuits do not receive enough warm water.

Faults in the thermostat sensor and actuator

Each room or zone typically has its own thermostat, which sends a command to the manifold 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 display an incorrect temperature, and the circuit will switch off too early.

Similarly, a faulty or seized actuator can remain in a closed position, meaning that specific circuit receives no warm water at all, 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 the temperature is changed — this indicates the actuator is moving.
• If the actuator doesn't move or make a sound, it is likely seized or faulty and needs replacement.

Insufficient circulation pump pressure

The circulation pump must be able to push water through all circuits, including the longest and most resistant one. If the pump is incorrectly chosen, too weak, or set to too low a speed, the furthest circuits will no longer receive warm water with sufficient pressure.

This typically manifests as rooms closer to the manifold heating up properly, but the furthest rooms consistently remaining 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 absent in some areas, some heat will escape downwards or sideways instead of rising into the room — this creates localised cold spots that are not related 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 basement or a ventilated sub-space, and another part above a heated room, heat loss will differ even with identical pipework.

Impact of floor covering material and thickness

Different floor coverings 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 often feels cooler, even though the pipework may be operating identically in both rooms — this is not a technical fault, but a natural difference in materials.

The impact of furniture and carpets on heat distribution

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

Similarly, thick carpets and rigid underlays significantly reduce heat transfer, so when placing carpets, it's worth considering where the heating circuits are located and which areas are intended as the primary heat emission points.

Step-by-step check before calling a specialist

A systematic approach helps to find the root cause of the problem faster and provides a lot of important information to the specialist upon arrival.

• Inspect the manifold — are all circuits open, and is any visibly closed or partially closed?
• Feel the temperature of the pipe at the manifold for each circuit — is any pipe significantly cooler than the others?
• Bleed each circuit individually until the flow is even and quiet.
• Check thermostats and ensure they display the actual room temperature correctly.
• Monitor any gauges or indicators on the manifold, if present, and note down differences between circuits.
• Map cold areas on a floor plan and note if they coincide with the location of any specific circuit.

When is it advisable to call a heating system specialist?

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

• If bleeding doesn't improve the situation and one circuit remains cold.
• If the manifold has no flow meters and balancing has never been performed.
• If you suspect an actuator or thermostat fault.
• If the problem appeared recently without any visible cause, for example, after a long shutdown over 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 is suitable for 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 repairing uneven heating in an already operating system, rather than choosing 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 if there was a long shutdown over summer.
• Order underfloor heating maintenance every couple of years to detect actuator and thermostat problems early.
• Consider where heating circuits are located when placing large furniture and thick carpets.

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, which in turn affects all circuits simultaneously.

In such cases, the problem is not necessarily in one specific room, but the entire house's underfloor heating feels warmer at times and cooler at others, 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, not just the manifold.

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

Varying room heating demand and thermostat settings

Each room has a different heating demand 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 might consistently feel cooler, even though the system is working correctly. This room simply needs a higher set temperature or longer operating time.

The outcome is also affected by whether thermostats are integrated into a single zone automation system or if each room operates independently — in an uncoordinated system, the warm and cold cycles of adjacent rooms can create the impression of a technical fault, when in reality, settings simply need to be adjusted on a room-by-room basis.

Impact of seasonal weather conditions on perceived unevenness

Uneven heating might feel more pronounced in spring and autumn than in mid-winter, as the system operates at lower power, and smaller differences between circuits become more noticeable. In mid-winter, when the entire system operates under a heavier load, the same inconsistencies may be less perceptible because all circuits receive more warm water.

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

What role does regular maintenance play in preventing unevenness?

Unlike conventional radiator heating, underfloor heating is concealed within a concrete slab or layer, which limits physical access to the pipework and makes problems invisible 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 a year later it turns out that a circuit's readings have significantly changed, the problem can be identified before it affects comfort or creates visible cold spots on the floor.

Many of the issues we discussed above — slight air accumulation, minor shifts in balance, early wear of an actuator — develop slowly over months. This is why an annual inspection before the start of the heating season is one of the most effective ways to keep the system working uniformly and prevent 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 over 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 until it becomes noticeable — early intervention is usually cheaper and faster.

Specifics of apartment buildings for uneven underfloor heating

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

In such a situation, it's worth 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 needs to be resolved by a specialist commissioned by the apartment association or building manager, rather than by adjusting an individual apartment's manifold.