If your underfloor heating is not working, first identify the pattern rather than the part. Is the whole system cold, only one room affected, the thermostat apparently calling for heat, or is an electric system tripping its protective device?
That distinction matters because wet UFH depends on the heat source, controls, manifold, actuators, circulation and individual pipe loops, while electric UFH depends on its electrical supply, thermostat, floor sensor and heating cable or mat.
Whole wet system is cold
Start with heat-source operation, system pressure, central controls and whether warm water is reaching the UFH manifold.
Only one room is cold
The fault is more likely to be local: thermostat demand, actuator or valve response, air, balancing or flow through that loop.
Thermostat says “on” but no heat
A heat-demand symbol does not prove that an actuator, pump, relay, heat source or electric heating element has actually responded.
Electric UFH trips repeatedly
Stop repeated resets. A competent electrician should test the circuit, thermostat and heating element for the cause.
Underfloor Heating Problems at a Glance
The symptom is not a diagnosis, but it gives you a sensible starting point. Use the table below to narrow the problem before any parts are replaced.
| What You Notice | Common Areas to Investigate | Best Next Step |
|---|---|---|
| No wet UFH heat anywhere | Boiler/heat pump, pressure, main controls, UFH pump, mixing arrangement, no hot primary flow | Check user controls and heat source; arrange diagnosis if the manifold is not receiving heat |
| One room or one zone is cold | Room thermostat, actuator, valve, loop flow, trapped air, balancing, local wiring | Compare that zone with working zones and avoid changing flow settings blindly |
| Manifold is warm but one loop has little/no flow | Actuator/valve, airlock, closed or restricted loop, balancing | Professional manifold and loop-flow assessment may be needed |
| UFH pump appears not to run | No demand, relay/control fault, power supply, seized or failed pump | Do not open electrical connections; arrange competent testing |
| Thermostat shows heat demand but floor stays cold | Wet: actuator/pump/wiring/flow. Electric: relay/sensor/supply/heating element | The output side of the control system needs checking, not just the display |
| Electric UFH trips the RCD/MCB | Damaged cable/mat, insulation fault, moisture, thermostat/circuit fault | Stop repeated resets and arrange electrical fault testing |
| Floor is slow, patchy or never gets warm enough | Normal thermal mass, low flow temperature, balancing, air, controls, floor covering, system design | Compare current behaviour with normal historical performance |
| Wet system pressure keeps falling | UFH or wider heating leak, PRV/expansion-vessel fault, other pressure-management issue | Investigate the cause rather than repeatedly topping up |
Safe Checks Before You Call an Engineer
There are several checks you can make without dismantling the system. The aim is to collect useful information, not to force valves, open controls or alter commissioning settings.
Checks You Can Usually Make
- Confirm whether the system is wet or electric
- Check the thermostat is powered, correctly scheduled and asking for heat
- Replace batteries in wireless controls if the manufacturer permits it
- Check whether the boiler or heat pump is operating and showing a fault code
- Observe the heating-system pressure gauge if you have a sealed wet system
- Compare the affected room with zones that are working normally
- Look for obvious water around an accessible manifold
- Note whether an RCD or breaker has tripped
Do Not Guess or Force
- Do not remove boiler covers
- Do not open wiring centres or thermostats to test live circuits
- Do not repeatedly reset an electrical circuit that keeps tripping
- Do not force stuck actuator pins or manifold valves
- Do not alter every flow meter to “see what happens”
- Do not drain or flush loops unless you understand the manifold and refill procedure
- Do not keep adding water to a system that repeatedly loses pressure
Underfloor Heating Not Working in One Room or One Zone
If most of the property is warm but one room or one UFH zone is not working, the heat source is less likely to be the main problem. The fault is usually somewhere between that room's thermostat and its corresponding circuit.
No Heat Demand
Incorrect programme, flat wireless batteries, loss of communication or a faulty thermostat can leave the zone closed even while other rooms heat normally.
Actuator or Valve Does Not Open
The actuator may have failed or the valve beneath it may be sticking, preventing flow through the affected loop.
Little or No Loop Flow
Air, a restriction, a closed valve or incorrect balancing can reduce flow even when the room is asking for heat.
Zone Signal Does Not Reach the Manifold
A wiring-centre or control fault can prevent the actuator and heat source from responding to the thermostat.
Manufacturer fault-finding guidance follows the same logic: confirm the thermostat is calling, confirm the corresponding actuator/valve responds, then establish whether water is actually flowing through the loop.
Underfloor Heating Not Working After Summer
A system that worked last winter but will not restart when the weather turns colder is a common fault pattern. The months without heating demand can expose components that no longer respond when they are asked to move or switch again.
Common after-summer causes
- Thermostat schedule or mode: summer settings, holiday mode or an old programme may still be active.
- Wireless thermostat batteries: a low-power control may display information but fail to communicate reliably.
- Sticking actuator or valve: a valve that has stayed in one position for months may not respond correctly when heating demand returns.
- Circulation pump problem: a pump may seize or fail after a period of inactivity.
- Control or communication fault: wiring centres, receivers and smart controls can lose settings or fail independently of the floor circuits.
- Heat-source problem: a boiler or heat pump fault may only become obvious once space-heating demand returns.
Wet Underfloor Heating Problems: Pump, Manifold, Actuator & Controls
Wet underfloor heating relies on several components operating in sequence. A thermostat creates demand, controls energise the relevant actuator and heat source, warm water reaches the manifold, and the pump and valves allow the correct flow through each loop.
Underfloor Heating Pump Not Working
If several or all zones are cold and the UFH circulation pump is not operating when there is genuine heating demand, possible causes include a control/relay problem, loss of electrical supply, a seized pump or pump failure.
A silent pump is not automatically a failed pump. It may simply not be receiving a demand. Professional diagnosis should therefore confirm the controls and supply before replacement is considered.
Underfloor Heating Manifold Problems
The manifold distributes water to the floor loops and is one of the most useful places to diagnose a wet UFH problem. Common manifold-related faults include:
- one or more flow meters showing little or no flow
- stuck or closed valves
- actuators not responding to room demand
- incorrect balancing between loops
- air trapped in a loop
- pump or mixing-valve problems
- visible leakage around accessible manifold components
If the water reaching the manifold is cold, the problem may be upstream in the heat source or primary heating circuit rather than inside the floor loops.
Underfloor Heating Actuator Problems
Actuators open and close individual manifold valves in response to room demand. A failed actuator, a control signal that never reaches it, or a valve pin that is sticking can leave one room cold while the rest of the system works.
The opposite can happen too: an actuator or valve that does not close correctly can leave a zone heating when it should be off. Proper testing checks the thermostat demand, control output, actuator response and underlying valve rather than replacing the actuator purely because the room is cold.
Underfloor Heating Thermostat or Wiring-Centre Problems
If the thermostat display is working, that only confirms part of the control chain. A wet UFH zone may still remain cold because the wiring centre, receiver, actuator output, pump relay or heat-source demand is not responding.
Air, Low Flow and Balancing Problems
Air can restrict a loop, but low flow can also result from a closed valve, poor balancing, a restriction or insufficient circulation. If a system has recently been drained or altered, trapped air becomes more likely. See the dedicated wet UFH bleeding guide for the difference between simple manifold venting and a full loop purge.
Electric Underfloor Heating Not Working
Electric UFH has no manifold, pump or water pressure. Fault-finding focuses on the electrical supply, thermostat, floor sensor, switching relay and the resistance/insulation condition of the heating cable or mat.
| Electric UFH Symptom | Possible Causes | What It Means |
|---|---|---|
| Thermostat is on but floor is cold | Thermostat relay, floor sensor, no load output, wiring fault, damaged heating element | The thermostat display alone cannot confirm that power is reaching a sound heater |
| RCD/MCB trips when UFH runs | Cable damage, insulation breakdown, moisture, thermostat or circuit fault | Requires competent electrical testing; stop repeated resets |
| Sensor error or implausible floor temperature | Failed, disconnected or damaged floor sensor; thermostat configuration | Sensor resistance and connections may need professional testing |
| Only part of the floor warms | Heating-element damage, installation/layout limitation, local floor-covering effect | Electrical test results and heat pattern help determine whether the element is intact |
Warmup's troubleshooting guidance similarly advises resistance testing of the heating element and checking thermostat output where the thermostat indicates heating but the floor remains cold. Those are electrician-level tests rather than homeowner checks.
Underfloor Heating Not Getting Hot, Warming Up Slowly or Heating Unevenly
Underfloor heating is designed to behave differently from radiators. A screeded wet system has significant thermal mass and can take much longer to respond after a deep temperature setback. Slow response is therefore not automatically a fault.
More likely to be normal behaviour
- the entire floor warms gradually rather than becoming hot quickly
- the system has just restarted after a long setback
- a thick screed or floor covering slows heat transfer
- the room ultimately reaches the target temperature and behaves consistently
More likely to need investigation
- one room behaves differently from equivalent zones
- performance has changed noticeably compared with previous seasons
- the room never reaches its normal target temperature
- flow is absent or very low on one loop
- the heat source is running but warm water is not reaching the manifold
- large cold patches appear where the floor previously heated evenly
Possible causes include incorrect flow temperature, poor balancing, trapped air, control faults, restrictions, changed floor coverings, heat-source issues or a system that is no longer meeting the building's heat demand.
Wet Underfloor Heating Losing Pressure or Suspected Leaks
Repeated pressure loss is a different fault from a simple cold zone. If a sealed heating system continually needs water adding, find out why the pressure is falling.
Possible causes include a visible or concealed leak in the UFH or wider heating circuit, a pressure-relief-valve problem, an expansion-vessel fault, leakage elsewhere in the boiler/heating system or an inaccurate pressure reading.
Clues Worth Recording
- cold and hot pressure readings
- how quickly pressure falls
- whether a particular UFH loop has changed
- visible dampness around the manifold or floor
- any boiler fault code
- whether water is discharging externally from the boiler
Relevant Specialist Help
How an Engineer Fault-Finds Underfloor Heating
A good UFH diagnosis follows the system in a logical order and uses the fault pattern to decide what needs testing. That reduces unnecessary part replacement and helps avoid disturbing finished flooring before there is evidence of a concealed fault.
Confirm the System and Fault Pattern
Wet or electric, one zone or every zone, intermittent or permanent, after summer or following recent building/heating work.
Check Demand and the Heat Source
Confirm that controls are asking for heat and, for wet UFH, that the boiler or heat pump and primary circuit can actually provide it.
Test the Relevant Components
Depending on the system this can include controls, wiring, actuator response, pump operation, manifold flow, valves, pressure behaviour, sensors and electric heater resistance/insulation.
Separate Accessible Faults from Concealed Faults
Only after accessible components and system behaviour are understood should a concealed pipe, cable or mat fault become the focus.
Explain the Repair Scope
The findings determine whether the solution is a control/component repair, loop purge/balancing, leak investigation, electrical repair or more targeted access to the floor.
Thermal imaging can be useful for comparing heating patterns or supporting leak/fault location, but it is one diagnostic tool rather than proof of the failed component. Hydraulic and electrical tests remain important.
Related Underfloor Heating Guides & Services
This page owns the broad troubleshooting intent. More specific problems should continue into the relevant guide or service rather than duplicating the same advice here.
Underfloor Heating Fault Diagnosis Across London & the Home Counties
If the checks above do not identify the problem, Fix & Repair Engineers provides professional wet and electric UFH fault diagnosis. The regional service pages below contain local coverage and booking information.
When booking, provide your postcode, whether the system is wet or electric if known, which rooms are affected, what the thermostat shows, any boiler fault code or pressure change, and photos of the manifold or controls where available.