Underfloor Heating Problems: Why It's Not Working & Repair Costs

1. Quick diagnosis: wet vs electric UFH

Before you touch anything, work out which system you have. It changes the entire diagnosis.

Wet (hydronic) UFH circulates warm water through pipes in the floor. It's fed from your boiler or heat pump through a manifold, with a circulation pump, a blending (mixing) valve and actuators on each loop. Faults sit in the manifold, pump, valves, boiler or pipework.

Electric UFH uses heating mats or cables under the floor, controlled by a thermostat with a floor probe (sensor). Faults sit in the thermostat, probe, cable or the RCD/breaker feeding it.

2. First checks anyone can do (5 minutes)

• Power: check the fused spur, breaker and RCD in your consumer unit. Electric UFH and the wet-system wiring centre both need power.
• Thermostat: is it set above the current floor temperature and actually calling for heat? A stat set to 20C in a 21C room won't fire.
• Mode and schedule: check it isn't in holiday/frost/off mode or sitting between scheduled "on" periods.
• Wireless stat batteries: flat batteries are one of the most common causes of "dead" UFH. Replace them.
• Be patient: wet UFH warms a whole floor slab, so it takes 1 to 3 hours to feel warm — not minutes. Many "not working" calls are simply impatience.

If the rest of your heating is dead too, the problem may not be the UFH at all — see central heating not working at all.

3. Only one zone/room not heating (wet)

If everywhere else is warm but one room stays cold, the fault is local to that loop:

• Stuck actuator pin — the small electric head on the manifold pushes a pin to open the loop. Pins can seize over summer. A common engineer check is removing the actuator and confirming the pin moves freely; it should spring back. This is a low-voltage manifold component, not part of the sealed gas circuit.
• Failed actuator — if the pin is free but the loop stays shut when the stat calls, the actuator is dead and needs replacing.
• Flow meter closed — the clear flow gauges on the manifold should show flow when that zone is on. A closed or zero-flow loop won't heat.
• Airlock — trapped air in one loop blocks circulation; that loop needs bleeding/flushing at the manifold, usually a job for a heating engineer.
• Faulty room stat — if it never sends the "call for heat" signal, the actuator never opens.

4. No zones heating / whole system cold (wet)

If the entire wet system is cold, look upstream:

• Boiler not firing — no heat source means no warm floor. Boiler faults are a Gas Safe job.
• Circulation pump dead or seized — no circulation, no heat. See typical circulation pump replacement cost.
• Pump relay on the wiring centre — if the relay fails the pump never gets the signal to run.
• Closed manifold isolation valves — flow/return valves accidentally left shut stop everything.
• Blending/mixing valve pin stuck — if the mixing valve jams shut, no warm water reaches the loops.
• No power to the wiring centre — check the spur and breaker.
• Low pressure — a system below ~1 bar may lock out. Here's how to repressurise a low-pressure boiler.

A stuck diverter is another whole-house culprit — see a stuck mid-position valve.

5. Pump runs constantly / UFH won't turn off

If the floor stays hot or the pump never stops:

• Stuck relay in the wiring centre keeping the pump powered.
• Dead stat battery — some wireless stats fail "on" (open) rather than off.
• Actuator stuck open — a failed-open actuator keeps a loop circulating regardless of the stat.

6. Pressure problems

Pressure dropping usually means a leak — and with UFH that can be under the floor, so take it seriously. If you can't see anything, read losing pressure with no visible leak.

Pressure rising is often a filling loop left open, or a failed expansion-vessel diaphragm. Either way it's worth a professional check rather than repeated top-ups.

7. Electric UFH not working

• Thermostat fault — a blank or unresponsive stat may simply need replacing.
• Floor probe (sensor) failure — a common fault. Many thermostats can be switched to air-sensing mode as a workaround, avoiding lifting the floor to replace a buried probe.
• RCD tripping — this points to insulation breakdown or a leak-to-earth in the cable, and needs an insulation-resistance (IR) test by a qualified electrician. Don't keep resetting it.
• Damaged cable — a break in the heating element; located by IR testing.
• Weak heat from flooring — carpet or thick covering over an electric mat throttles the heat (see TOG, below).

8. Floor feels warm but the room is cold / takes forever

Heat that never quite arrives is often a design or flooring issue, not a fault:

• Undersized system for the room's heat loss.
• High-TOG floor covering — thick carpet/underlay insulates the heat in the floor. As a rule, keep a single carpet to around 1.5 TOG; on a boiler-fed wet system the combined carpet-plus-underlay value should typically not exceed roughly 2.5 TOG (heat-pump systems are usually held to about 1.5 TOG), but always follow the manufacturer's figure.
• No insulation board under the screed, so heat goes downwards.
• Flow temperature set too low on the blending valve. UFH typically runs a blended flow of around 40–55C (vs 60–80C for radiators); set too low, the floor never gets up to temperature.

9. UFH repair costs (UK, 2026)

Indicative ranges only, last checked 2026 — actual prices vary by region, system and contractor, and emergency or out-of-hours work costs more. Always get a written quote from your own engineer; these figures are for guidance, not a quotation.

Job	Part	Labour
Replacement actuator	£10–£25	Often within a call-out
New UFH thermostat	£40–£200	£60–£150
Circulation pump	£100–£300	£100–£200
System / chemical flush	~£350–£800 (full power flush typically more — see below)
UFH leak detection	commonly ~£300–£600 for a straightforward domestic case; hidden or complex leaks (e.g. tracer-gas) can run higher
Recalibration / rebalancing	£40–£80
Annual service	£100–£200
Engineer call-out	~£40–£70/hr (emergency higher)

For a heavily sludged system, see power flush cost and our guide to sludge in the heating system.

10. Should boiler cover or home-emergency insurance pay for UFH repair?

This is where many homeowners get caught out. Most standard boiler cover excludes underfloor heating. Saga, for example, states that its home and heating emergency cover does not include repairing or replacing parts of underfloor heating systems, and several insurers limit cover to a gas-fired radiator system only. Exclusions and wording change, so always check the current policy document — verify on the provider's own page before relying on it.

Some central-heating cover may include the wet UFH manifold and pump if they're part of the gas heating system — but read the wording carefully, as this varies by provider. See central heating cover that includes the pump and manifold and what boiler cover doesn't cover.

A leak under the floor usually needs "trace and access" cover — this pays to locate and reach the leak (and reinstate the floor afterwards), often via your buildings insurance rather than boiler cover. Limits are commonly in the region of £2,000–£10,000, but check your own policy.

Before buying, check: does it cover UFH at all? The manifold, pump and actuators? Trace and access for hidden leaks? Electric mats/cables (usually excluded)?

11. When to DIY vs call a professional

A few checks are safe for a homeowner: replacing stat batteries, resetting the thermostat, checking breakers/RCD, and repressurising within the normal range. Confirming a manifold actuator pin moves is borderline — if you're unsure, leave it to an engineer.

Call a professional for everything else:

• Electric UFH faults (RCD tripping, cable/probe) — a qualified electrician.
• Wet/pressurised work (pump, valves, leaks, flushing, bleeding loops) — a plumber or heating engineer.
• Anything involving the boiler, burner, flue, gas valve, PCB, sealed circuit or pressure-relief valve — a Gas Safe registered engineer ONLY. Never attempt work on the gas appliance or sealed circuit yourself.

12. How to prevent UFH faults

• On wet systems, keep the water dosed with central heating inhibitor and consider a magnetic filter to catch sludge.
• Run the system briefly in summer (or "exercise" the actuators and pump) so pins and bearings don't seize.
• Have an annual check to confirm pressure, flow rates and blending temperature.
• Never lay carpet or covering over an electric mat beyond its TOG limit.

This article is general information, not financial or gas-safety advice. We compare a selected panel of providers, not the whole market, and may earn a commission if you buy through our links. Always have gas appliances checked and repaired by a Gas Safe registered engineer; in a gas emergency call 0800 111 999. Prices are indicative UK guides for 2026 — confirm current prices on the provider's own site.