Summary

This guide is scoped purely to repairing and diagnosing faults in an existing underfloor heating (UFH) system — screed-buried leaks, manifold and pump faults, actuator failures, and electric mat/cable element breaks. It does not cover pricing a new UFH installation; for that, see underfloor heating pricing guide (wet systems, new-build/screeded) and electric underfloor heating pricing guide (electric mat/cable, new install).

UFH repair pricing is dominated by one fact: the heat-emitting element is buried under a finished floor, so the hardest and most expensive part of almost every repair is finding the fault, not fixing it. A pinhole leak in a screed-buried pipe, or an open-circuit break in an electric heating mat, can be anywhere under several square metres of tile, screed or floating floor. Guessing and breaking out floor speculatively is expensive, disruptive, and can make things worse. Proper fault-finding — pressure decay testing and thermal imaging for wet systems, insulation-resistance and continuity testing for electric systems — narrows the search to a small, defensible area before any floor comes up.

The second thing that separates competent UFH repair pricing from a bad guess is knowing which faults are genuinely repairable in-situ and which aren't. A single pinpointed leak in a wet loop can often be repaired with a screed-rated coupling and a small patch of reinstatement. Multiple failures, a leak that can't be pinpointed after reasonable investigation, or a badly corroded or degraded pipe run usually means abandoning that loop and re-routing rather than chasing an increasingly expensive repair. The same logic applies to electric mats: a single accessible break can sometimes be spliced, but a mat with multiple faults or one embedded under large-format tiles is usually more economically replaced outright than repeatedly repaired.

Key Facts

Quick Reference Table

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Fault type Diagnostic method Trade cost Typical quoted price
Diagnostic visit — wet system (pressure test + thermal imaging) Half-day specialist visit £120–£230 £250–£380
Diagnostic visit — electric system (insulation resistance + continuity) Half-day visit £70–£120 £150–£250
Electric mat/cable — localised splice repair Fault located, minor floor lift £190–£390 £280–£550
Electric mat — full replacement (small bathroom, ~5m²) See electric underfloor heating pricing guide — ~£450–£850
Wet UFH — pinpointed leak, break-out and coupling repair Fault located, localised screed break-out £440–£790 £650–£1,200
Wet UFH — loop abandoned and re-routed (unlocatable/multiple leaks) Fault not pinpointed £500–£900 £750–£1,400
Pump replacement Component swap £90–£180 £150–£320
Actuator head replacement (per zone) Component swap £85–£165 £130–£280
Manifold/blending valve fault Component repair/swap £120–£250 £200–£420
Wiring centre/thermostat fault Component swap £70–£150 £120–£280

Detailed Guidance

Diagnosing a wet UFH fault before touching the floor

Start with a pressure test: isolate the affected zone at the manifold, pressurise to the system's test pressure, and monitor the gauge over at least 24 hours. A steady, measurable drop confirms a leak in that loop (rather than, say, an air lock or a faulty manifold seal). Once confirmed, thermal imaging after a heating cycle is the standard non-invasive way to narrow the location — look for a cooler patch (the leak is losing water/heat locally) once the rest of the floor has come up to temperature. Where the floor covering or screed thickness defeats thermal imaging, acoustic or trace-gas detection from a specialist leak detection company is the next step — factor this into the diagnostic quote for anything beyond a straightforward domestic single-storey slab.

Repairing a pinpointed wet UFH leak

Once located, the repair itself is usually the cheaper part of the job: break out a small area of screed around the fault, expose the pipe, and fit a screed-rated repair coupling designed for encasement (not a standard plumbing compression fitting, which isn't rated to be buried). Reinstate with a fast-setting repair screed or self-levelling compound and match the floor finish. Pressure-test the repaired loop again before final reinstatement to confirm the fix has held.

When a leak can't be pinpointed — abandon and re-route

If thermal imaging and acoustic detection don't produce a confident fix on the fault location, or if there are multiple failure points in the same loop (common on an older, degraded pipe run), the economically sound repair is usually to isolate and abandon that loop at the manifold and run a new pipe to cover the affected area, rather than repeatedly breaking out screed chasing an elusive leak. This costs more up front but avoids the far higher cost of repeated call-backs and floor damage.

Electric mat and cable faults

Confirm the fault type first: continuity testing tells you if the element is open-circuit; insulation resistance testing tells you if there's a breach to earth (usually moisture ingress at a puncture point). A single accessible break in a loose cable system can sometimes be spliced with a proper embedding-rated splice kit and a small tile/floor lift. Mat systems are generally less forgiving — the foil backing and tighter element spacing make a clean in-situ splice harder, and a fault in a mat under large-format tiles often means the economics favour replacing that zone's mat rather than chasing a repair. Always test the repaired or adjacent sections again before reinstating flooring.

Component faults — pumps, actuators, manifolds, controls

Not every UFH "not heating" call is a buried fault. Pump failure (no circulation), stuck or failed actuator heads (a zone stuck open or closed), a faulty blending valve (wrong flow temperature to the floor), or a failed wiring centre/thermostat are all straightforward component-level repairs that don't require opening the floor. Always rule these out with basic diagnostics — is the pump running, are actuators clicking open on call for heat, is the correct flow temperature reaching the manifold — before assuming a buried leak or element fault and quoting for the more expensive invasive work.

Worked pricing example

A single-zone wet UFH kitchen loop shows a steady manifold pressure drop over 24 hours with no visible damp patch upstairs. A diagnostic visit with thermal imaging pinpoints a cool patch near an appliance run.

Trade cost (materials + labour, before markup):

Quoted price to customer:

This sits within the £650–£1,200 quoted range for a pinpointed wet UFH leak repair given in the Quick Answer — at the lower end of the range, reflecting a straightforward, easily-accessed single fault.

Frequently Asked Questions

Should I charge separately for the diagnostic visit?

Yes, and say so up front. Fault-finding on a buried system is genuine billable work — pressure testing, thermal imaging, and analysis take real time and specialist equipment, independent of whether a repair follows. Many tradespeople credit some or all of the diagnostic fee against the repair cost if the customer proceeds, which reads as fair to the customer while still covering your time if they don't.

Is it ever right to replace rather than repair?

Yes. If an electric mat has multiple faults, or a wet loop has failed more than once in different locations, the cost of repeated break-out, testing and reinstatement usually exceeds the cost of replacing that zone outright — and a replacement removes the risk of a further comeback on an ageing system. Compare the repair quote honestly against underfloor heating pricing guide or electric underfloor heating pricing guide for that zone's size before committing the customer to another repair.

Can I repair a wet UFH leak without breaking out the screed?

Not reliably. There are proprietary leak-sealant additives marketed for wet heating systems, but they're not a substitute for a proper mechanical repair on a UFH loop and are not something to rely on for a customer-facing repair — treat them as, at best, a temporary measure while a proper repair is scheduled, and say so clearly.

What's the biggest pricing mistake on UFH repair?

Quoting a fixed repair price before fault-finding is complete. Because the fault location and repair method (localised coupling repair vs full loop abandonment and re-route) can differ by a factor of two or more, a fixed quote given before diagnosis either under-prices the job if it turns out to be a multi-point failure, or over-prices it and loses the job if it turns out to be simple. Quote the diagnostic stage first, then a firm repair price once the fault is located.

Regulations & Standards