Boilers & Heating
Annual boiler service
TL;DR
An annual service is what keeps your warranty valid, catches small problems before they become big ones, and typically saves 3-5% on your gas bill. A proper service takes 45-60 minutes on site — anything faster is a visual glance, not a service.
Every manufacturer — Worcester, Vaillant, Ideal, Baxi, Viessmann, Alpha — makes annual servicing a condition of their warranty. Skip a year and if something fails they'll refuse the claim. That's the boring reason to book one. The interesting reason is that a real service, done to the manufacturer's checklist, finds the small faults that cause winter breakdowns: dirty burners, worn ignition electrodes, weeping seals, expansion vessels that have lost half their pre-charge.
This page explains exactly what we check, what a service costs, and what an honest service report looks like — including the ones where we tell you the boiler is fine and just needs another year on the clock.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
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What actually happens during a proper annual service?
Manufacturer service schedules vary slightly but the core checks are consistent. A KJ annual service always covers the following, and the results are recorded on the Benchmark service page in your boiler booklet so the warranty stays valid:
- Combustion analysis with a calibrated flue gas analyser (CO/CO₂ ratio to manufacturer's spec)
- Visual inspection of the flue, terminal and seals internally and externally
- Removal and inspection of the burner and heat exchanger where required by the MI
- Check and re-charge of the expansion vessel to spec (usually 0.75-1.0 bar)
- Inspection of the condensate trap and pipe (cleared if silted)
- Operational test of the safety devices — PRV, overheat thermostat, flame ionisation
- Check of gas working pressure and standing pressure at the boiler inlet
- Check of system inhibitor level with a test strip (top-up if depleted)
- Full functional test on both central heating and hot water demand
- Written service report, Benchmark page signed, and any advisories flagged
How long should a proper boiler service take?
45-60 minutes on site is normal. A landlord gas safety check (CP12) with a service on the same visit is typically 60-90 minutes. If someone quotes you a "15-minute service" they are doing a visual inspection and signing a book — that is not a manufacturer-spec service and it will not defend a warranty claim.
When is the best time to book a service?
Late spring and summer. Two reasons: engineers are less stretched so you get more of their time, and if anything is flagged as an advisory we can fix it before winter demand exposes it. Booking a service in November when your boiler has just failed defeats the point.
We send an annual service reminder by email the month before yours is due, so you don't have to remember.
How do you keep the warranty valid?
Three things, every year: a manufacturer-spec service by a Gas Safe engineer, the Benchmark service page signed and dated, and the inhibitor topped up if depleted. If those three boxes are ticked, no major manufacturer will refuse a warranty claim on service grounds.
Landlord gas safety check (CP12) — is that the same thing?
No. A CP12 is a legal safety check every landlord has to arrange every 12 months on every gas appliance in a rented property. It confirms the appliance is safe. A service confirms the appliance is running efficiently and to spec. They overlap but a CP12 alone does not satisfy your boiler warranty. We usually do both together on the same visit for landlords — one price, two certificates.
Typical prices
Real-world ranges from recent Northwest jobs. Your final price is confirmed in writing before any work starts.
| Item | Typical price | Notes |
|---|---|---|
| Annual boiler service | 85 – 120 | 45-60 mins on site |
| Annual service + smart stat check | 110 – 145 | Includes Nest/Hive/Tado check |
| Landlord CP12 (one appliance) | 75 – 95 | Certificate emailed same day |
| Landlord CP12 + service combined | 130 – 165 | One visit, two certificates |
| Additional appliance on same CP12 | 25 – 35 | Cooker, fire, etc. |
| Powerflush recommended after service | 450 – 650 | Only if system water is dirty |
| Filter fit during service | 180 – 260 | One-off if no filter fitted |
| Inhibitor top-up | 35 – 55 | Included free if level is borderline |
Which brand should you fit?
We service all common UK brands to their own MI: Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann, Alpha, Glow-worm, Potterton. We don't push service plans that lock you in — you book each year as it comes due. We install and service Worcester Bosch, Vaillant, Ideal, Baxi, Viessmann and Alpha — none of them pay us commission and we don't push a "boiler of the month".
Our promise on this job
Flat £50 diagnostic — deducted in full from any work booked. Fair, transparent quote before we start. If we can't fix the fault we diagnosed, we refund the diagnostic. All gas work is signed off by a Gas Safe registered engineer.
Talk to KJ about annual boiler service
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