How to Price a Boiler Repair: Common Faults, Parts and Call-Out Rates

Quick Answer: UK boiler repair pricing splits into call-out (£75–£150 typical), labour (£60–£90/hour), parts (£30–£500+ depending on fault), and post-repair Gas Safe certification. A typical no-heat repair runs £180–£450 all-in for common faults (PRV, expansion vessel, diverter valve), £450–£900 for heat exchanger or PCB replacement. All work must be by a Gas Safe registered engineer; parts must be manufacturer-OEM or matched-OEM-spec, and the work documented on the Gas Safe certificate including any safety check carried out.

Summary

Boiler repair pricing is constrained by gas safety regulation in a way few other trades are. Only a Gas Safe registered engineer can legally work on the gas-side of a UK boiler, the customer always sees a documented certificate, and the manufacturer's parts catalogue is largely controlling on what can be replaced and at what cost. This narrows the room for price spread but makes pricing more transparent than most trade work — most repairs fall into a predictable cost band by fault type.

This guide gives realistic 2026 UK pricing for the 12 most common combi and system boiler faults, the components most often replaced (with retail and trade prices), the labour time per fault, and the warranty implications of repair vs replacement decisions. It includes the criteria for "beyond economic repair" — typically when the cost of a fix exceeds 50–60% of replacement cost, or when the boiler is over 12 years old and out of manufacturer parts support.

The single most valuable data point for a pricing customer: the call-out fee covers diagnosis only, and parts/repairs are extra. A quote that bundles "call-out, diagnosis and most repairs from £150" is almost always under-quoted on the most common high-cost faults (heat exchanger, PCB, diverter valve), and the customer ends up paying significant additional amounts. Transparent pricing — call-out separate, labour by hour, parts at cost+markup — builds trust faster than a misleading bundled rate.

Key Facts

Quick Reference Table — Common Faults and Realistic Pricing

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Fault Typical Symptom Parts Cost Labour Total
Low pressure <1 bar reading £0–£140 £60–£140 £75–£280
PRV leaking Drip from outside drain pipe £25–£60 £80–£140 £180–£280
Diverter valve stuck No hot water but heating works (or vice versa) £80–£200 £150–£250 £280–£550
Plate exchanger scaled Slow hot water, kettling £180–£450 £150–£280 £400–£900
PCB failure No display, won't fire, intermittent £180–£450 £80–£140 £350–£700
Pump failure No flow, hot boiler / cold rads £80–£250 £140–£280 £280–£600
Expansion vessel Pressure swings up and down £45–£140 £140–£280 £210–£500
Fan motor Boiler firing then locking out £140–£350 £140–£280 £350–£750
Flue/condensate frozen "F1", "F22" or similar lockout £0–£40 £80–£140 £150–£300
Sludge / scale (system) Cold patches on rads, kettling £350–£600 included £450–£800
Gas valve Won't fire, no spark/no gas flow £180–£400 £140–£280 £400–£750
Primary heat exchanger Severe corrosion, leaks £350–£900 £200–£400 £700–£1,400

Detailed Guidance

Call-out vs labour vs parts — pricing transparency

Three components, separately priced:

Call-out fee: Fixed fee that covers the engineer arriving on site and carrying out initial diagnostic. Typically £75–£150. Should include up to 30 minutes diagnostic time. If repair completed within the call-out time, that's all the customer pays plus parts.

Labour: Beyond the call-out time, hourly or half-hourly rate. £60–£90/hour standard; £90–£140/hour weekends and out-of-hours. Round to nearest 30 minutes for billing.

Parts: Manufacturer or matched-OEM, with markup typically 15–35% over trade price. Itemise on the invoice with part number and price.

A transparent quote: "Call-out £95, labour £75/hour, parts at trade + 25%, Gas Safe certificate included."

A confusing quote: "Most repairs from £150" — vague, customer feels misled when actual cost emerges.

Common fault — low pressure

System pressure below 1 bar = no heat (boiler locks out for safety). Customer often resolves by re-pressurising via filling loop. If pressure drops repeatedly:

Diagnostic procedure: re-pressurise, observe rate of pressure loss, check PRV outlet for water (indicates pressure was over-high and expansion vessel may be failed), look for visible system leaks. If no obvious cause, isolation test pulls suspect components in turn.

Common fault — diverter valve failure

A combi has a diverter valve that switches the primary water flow between heating and DHW circuits. Stuck or worn valves produce:

Diagnosis: thermal imaging or simple touch-temperature on the heat exchanger pipe outputs. With heating call active, both pipes should be hot in heating mode. If only one pipe is hot when both should be, valve isn't fully diverting.

Fix: replace diverter valve. Typically £80–£200 in parts, £150–£250 labour (drain primary, isolate gas, remove side panel, replace valve, re-fill, vent, bleed, test).

Common fault — plate heat exchanger (DHW) scaling

Combi boilers have a plate heat exchanger transferring heat from primary circuit to mains DHW. In hard water areas this scales over 3–8 years, reducing flow rate and heat transfer.

Symptoms:

Fix: descale or replace plate. In-situ chemical descale £180–£300 (uses citric or sulphamic acid pumped through DHW circuit). Replacement plate £180–£450 supply + £150–£280 labour. For severely scaled units, replacement is more cost-effective than descale.

Common fault — PCB failure

PCB (Printed Circuit Board) controls all boiler operations. Failures range from intermittent display flickering to complete dead boiler. Common causes:

Diagnosis: the engineer reads boiler error codes via the display or via diagnostic mode. Many PCBs report fault codes that point directly to the issue.

Fix: replace PCB. £180–£450 supply (manufacturer-specific) + £80–£140 labour (typically a 30-60 minute swap). Boiler may need re-commissioning after PCB replacement, especially for combi-vs-system or output settings.

Common fault — pump failure

Heating circulation pump fails mechanically (bearings, impeller) or electrically. Symptoms:

Fix: replace pump. £80–£250 supply (Grundfos, Wilo, manufacturer-specific) + £140–£280 labour (drain system, isolate, replace pump, refill, vent, bleed, test).

For a system that's never been powerflushed, replacing the pump might be a temporary fix if the pump is failing due to sludge contamination — also recommend powerflush.

Common fault — sludge and scale

Black magnetic sludge in the system (iron oxide from internal corrosion) and scale in the heat exchanger (calcium carbonate from hard water) frequently coexist. Symptoms:

Fix: powerflush + chemical clean + new inhibitor + magnetic filter. £450–£800 typical; takes 4–8 hours. For severe sludge, two flush cycles needed.

A magnetic filter (Magnaclean, Adey, Spirotech) installed during the flush prevents recurrence — and is mandatory under Boiler+ regulations 2018 on any new boiler installation.

Beyond economic repair (BER)

When repair cost exceeds replacement cost trigger threshold, replacement makes more sense:

Boiler Age BER Threshold
0–5 years Always repair (likely under warranty)
5–10 years Repair if cost <60% of replacement
10–15 years Repair if cost <40% of replacement
15+ years Replacement usually cheaper long-term; parts increasingly unavailable

Replacement costs:

For a 12-year-old boiler with a £900 repair quote, replacing for £2,500 is often the better long-term value once you factor in:

Annual service — the recurring revenue

A boiler service is £75–£140 typical. Includes:

Customers booking annual service are 3–4× more likely to call the same engineer for a repair when something goes wrong. Annual service is also a manufacturer warranty requirement on most premium boilers — skipping a service voids warranty.

For tradespeople, structuring a maintenance agreement at £100–£140/year that includes the annual service plus a discount on repair parts creates predictable recurring revenue. A typical heating engineer with 200 maintenance customers generates £20,000+/year before any repair work.

For homeowners — what to expect

A reasonable boiler repair quote should:

Red flags:

For repairs over £500 it's worth getting a second opinion, particularly if the engineer is recommending replacement. A second Gas Safe engineer can confirm or refute the diagnosis.

Frequently Asked Questions

Should I repair an old boiler or replace it?

Calculate: if the repair cost exceeds 50–60% of replacement cost AND the boiler is over 10 years old, replacement is usually better value long-term. New boilers offer 5–10 year warranties, 15–25% efficiency improvement (saving £200–£400/year on bills), and fewer ongoing repair costs. For boilers under 10 years old with a £200–£400 fault, repair is almost always the right answer.

Can I claim against the manufacturer warranty for the repair?

If the boiler is in warranty and has been annually serviced (manufacturer warranty almost always requires service history), yes — most repairs are covered. The customer or installer contacts the manufacturer directly; manufacturer dispatches a registered engineer. Your independent engineer cannot claim warranty work on someone else's installation.

Why is the call-out fee separate from labour?

Call-out covers the engineer arriving on site, even if the issue is resolved in the first 30 minutes. It also covers travel time and vehicle costs. Bundling it into labour rate confuses customers when a quick visit costs the same as a longer one. Transparent separation is fairer to both parties.

What's a fair markup on parts?

Industry typical is 15–35% above trade price. Higher markup for emergency callouts where parts are sourced at premium urgency. Lower markup for planned work where parts can be ordered ahead. For a £200 trade-price part, retail of £230–£270 is fair; £400+ would be excessive.

Do I need to be there for the boiler service?

Ideally yes — the engineer can ask questions about how the system performs and you can ask about anything you've noticed. If absent, leave clear access instructions and confirm the engineer can certify the work without verbal feedback. Most services take 30–60 minutes.

Regulations & Standards