Every boiler service is carried out to that appliance manufacturer’s own instructions, so the exact checklist varies by make and model. “Standard” and “full” aren’t industry-wide definitions either — they’re the names of the two service levels we offer at The Happy Heating Co. Our standard service is the annual safety and performance check: a Gas Safe registered engineer tests gas tightness, runs a flue gas analysis, checks the controls and system pressure, cleans the condensate trap and checks the expansion vessel, then leaves you a written record. Our comprehensive (full) service adds a strip-down and internal clean where the manufacturer’s instructions provide for it, with seals replaced and the electrodes checked or renewed. Most boilers in good condition need only the standard service each year. We’re Gas Safe registered (657972) and we’ll tell you honestly which one your boiler actually needs — see our boiler servicing page.
A quick note on terminology before we start: there’s no single industry definition of a “full” boiler service, so the phrase means different things at different companies. What follows describes our two levels, and what each one includes in practice.
What does our standard boiler service include?
Our standard service is a full safety and efficiency check, not a glance and a wipe. Following the manufacturer’s schedule for your appliance, our engineers:
- Test gas tightness — confirming there are no gas leaks on the installation.
- Run a flue gas analysis — measuring combustion to confirm the boiler is burning cleanly and safely (something a visual check simply can’t tell you).
- Check the flue and air intake visually for any issues.
- Check controls and system pressure — and here’s a catch worth knowing: many boilers have no low-water-pressure sensor, so they’ll quietly keep running at low pressure without ever flagging it. The annual service is often where that’s first caught.
- Clean the condensate trap — a blocked trap is one of winter’s most common breakdown causes, and it’s a step rushed services skip.
- Check and recharge the expansion vessel — a flat vessel causes pressure swings and drips from the pressure relief valve.
- Leave a written service record — useful evidence for a guarantee claim, and a clear picture of the boiler’s health.
For most boilers that are serviced every year and running well, this is all that’s needed.
What does our full boiler service add?
Our full service — we call it the comprehensive service — includes everything above, and then the boiler is opened up properly, to the extent the manufacturer’s instructions for that model provide for:
- A strip-down and internal clean of the boiler.
- Seals replaced, so the casing and combustion seals aren’t relying on tired components.
- Electrodes checked or replaced — worn ignition electrodes are behind plenty of “boiler won’t fire” call-outs.
The difference is the depth. A standard service confirms the boiler is safe and running properly; a full service physically renews the wear parts and cleans out what’s accumulated inside. It takes longer and costs more, which is exactly why it isn’t the right answer for every boiler every year — and why we’d rather tell you straight which one yours needs than sell everyone the bigger visit.
When is a full service worth it?
A full service makes sense when one or more of these applies:
- The boiler is getting on — an older appliance that’s had years of use benefits far more from a strip-down than a two-year-old boiler does.
- It’s missed services — if it’s been several years (or you’ve just moved in and there’s no service history), a full service brings it back to a known-good baseline.
- It’s running rough — struggling to fire, cutting out, or burning noticeably less cleanly than it should.
- You want maximum life from it — renewing seals and electrodes before they fail is cheaper than the call-out when they do.
If none of those apply, book the standard service and keep your money — that’s the honest advice, and it’s the same advice we give on the doorstep.
What neither service fixes: a sludged-up system
One important distinction, because it catches a lot of people out. Both service levels look after the boiler itself. If your problem is cold spots on radiators, a slow-to-warm system or repeat component failures, one likely explanation is sludge — the black magnetite that builds up as the central-heating system corrodes internally — which lives in your radiators and pipework rather than inside the boiler casing. Sludge is an important cause of circulation and component problems, though restricted valves, a failing pump, trapped air or poor system balancing can produce similar symptoms.
That’s why the order matters: test first, then treat. The right next step is assessing the system water and how well the circuit is circulating, and only then cleaning it — proportionately to what’s actually found. A powerflush is the appropriate answer when significant contamination has been confirmed, not an automatic response to a cold radiator. The ongoing defences are a correctly dosed corrosion inhibitor and a magnetic filter.
Worth being clear about what a service does and doesn’t cover here. We check the system water and the magnetic filter on both service levels — that’s where the expensive problems tend to announce themselves early. What isn’t automatically included is testing or topping up the corrosion inhibitor, because a service follows the boiler manufacturer’s schedule and inhibitor work sits outside it. If your symptoms point that way, we’ll say so and explain what testing involves — our boiler repairs team deals with it every week.
Renting or letting?
If you’re a tenant, boiler servicing is your landlord’s responsibility — report problems rather than booking work yourself. If you’re a landlord, remember the annual Landlord Gas Safety Check (CP12) is a legal safety inspection, not a service — many landlords book the CP12 and a service together in one visit, and an older boiler in a rental earns a full service for the same reasons as any other: fewer mid-tenancy breakdowns.
Frequently asked questions
What does a standard boiler service include?
Our standard service covers a gas tightness test, flue gas analysis, flue and air-intake checks, controls and system pressure checks, cleaning the condensate trap, checking and recharging the expansion vessel, and a written record — carried out by a Gas Safe registered engineer to the manufacturer’s schedule for your appliance.
What is a full or comprehensive boiler service?
In our case, everything in the standard service plus a strip-down and internal clean, replacement seals, and the ignition electrodes checked or replaced, where the manufacturer’s instructions provide for it. There’s no industry-wide definition of a \”full\” service, so it means different things at different companies.
How do I know which service my boiler needs?
A newer boiler that’s serviced every year normally only needs the standard service. Consider a full service if the boiler is older, has skipped services, has no service history, or is struggling to fire or running rough. We’ll tell you honestly which yours needs — not everyone needs the bigger visit.
Will a full service fix cold radiators or a sludged system?
No — that’s a different problem. Both service levels look after the boiler itself. Cold radiator patches can indicate sludge in the heating circuit, but restricted valves, a failing pump or trapped air can look similar, so the system water and circulation should be assessed first, then cleaned proportionately if contamination is confirmed.
How much does a boiler service cost?
A one-off gas boiler service typically costs £80–£120 across the UK in 2026, averaging about £100 (Checkatrade, March 2026), with London toward the upper end — market figures for budgeting, not a quote. A comprehensive strip-down service costs more because it takes longer and includes parts. Our prices are on our boiler servicing page.
Does servicing keep my boiler guarantee valid?
It’s commonly a condition of it, but your manufacturer’s terms decide — including what the service must cover and how it’s recorded. Check the exact current requirements for your make and model rather than assuming either service level qualifies. We keep a digital service record for every boiler we look after.
How long does each service take?
A standard service usually takes around 30 to 60 minutes on a boiler in good condition. A full service takes longer because the boiler is stripped down and cleaned — we’ll give you a realistic time when you book so you can plan around it.
Book the right service — we’ll tell you which one
Not sure which your boiler needs? Tell us its make, age and history and we’ll give you a straight answer.
- WhatsApp us — Book in 60 seconds
- Call 020 8051 2124 — our line is answered 24/7 and we’ll get your details to an engineer
- Book online: boiler servicing
We’re Gas Safe registered (657972) and service boilers across West and North West London. Heating that just works, no drama.
About the author Adam Said is a Gas Safe registered domestic gas engineer (657972) at The Happy Heating Co, servicing, repairing and installing boilers in homes across West and North West London. This guide reflects what we see on real jobs every week.
Related reading
- How often should you service your boiler?
- Boiler servicing in West London
- Boiler repairs
- Landlord Gas Safety Certificates (CP12)
Cost figures are typical UK market averages from Checkatrade’s March 2026 boiler service cost data, for budgeting only — not a quote. Guarantee conditions vary by manufacturer, model and installer scheme; check the exact current terms for your own boiler. We confirm the exact cost before any work begins.
