If your boiler is not serviced every year, you may be exposing your home, your tenants, and your property investment to serious—and often expensive—risks.

Annual boiler servicing isn’t just a recommendation; it’s a key part of maintaining efficiency, safety, and long-term reliability.

If you’re unsure how often you should service your boiler, understanding the recommended servicing intervals can prevent most of the risks outlined below.

In this guide, I’ll break down exactly what happens when a boiler isn’t serviced annually, why issues arise, what causes them, and what you can do about them.

What Happens If a Boiler Is Not Serviced Every Year?

A boiler not serviced every year can gradually develop internal issues that go unnoticed until they cause serious faults, breakdowns, or safety hazards.

Annual servicing inspects combustion quality, gas safety, efficiency, and internal component health—so skipping it disrupts this protection.

For a clearer picture of the checks involved, this guide on what a boiler service includes explains exactly what Gas Safe engineers inspect and why each step matters.

Below, we outline the 7 major risks, what causes them, and how to fix them.

1. Reduced Boiler Efficiency

A boiler not serviced every year becomes less efficient because internal components accumulate soot, scale, and system debris.

Cause 1: Soot Build-Up in the Burner

Soot build-up restricts combustion, forcing the boiler to burn more gas to achieve the same heat output.

How to Fix Soot Build-Up

• A Gas Safe engineer must dismantle and clean the burner assembly.
• Combustion levels need recalibrating using flue gas analysis.
• Replace the burner gasket if worn to prevent air leaks.

Cause 2: Limescale Accumulation in the Heat Exchanger

Limescale, especially in hard-water areas, insulates the heat exchanger and forces the boiler to overheat.

How to Fix Limescale Build-Up

• Heat exchanger descaling using acid-based cleaners (professional-only).
• Installing a scale reducer or magnetic filter to prevent recurrence.
• In severe cases, replacing the heat exchanger entirely.

2. Increased Risk of Breakdowns

A boiler not serviced every year gradually develops unnoticed wear on internal components, increasing the likelihood of sudden and costly failures.

Cause 1: Worn Ignition Electrodes

Electrodes degrade over time, causing intermittent ignition failure.

How to Fix Worn Electrodes

• Engineer replaces electrodes and adjusts spark gap.
• Check PCB communication with ignition system.
• Ensure gas pressure is correct at the appliance.

Cause 2: Faulty Fans or Pumps

Fans and pumps must run smoothly; lack of servicing leads to friction, seizing, or electrical failure.

How to Fix Fan or Pump Failure

• Engineer tests voltage supply and impeller movement.
• Replace worn bearings or full components.
• Lubricate moving parts where model-compatible.

3. Higher Energy Bills

A boiler not serviced every year forces the system to work harder due to blockages, poor combustion, and reduced heat transfer.

Cause 1: Poor Combustion Efficiency

When combustion isn’t checked, the boiler burns gas inefficiently.

How to Fix Poor Combustion

• Engineer adjusts gas valve for correct air-to-fuel ratio.
• Replace faulty burner or injectors.
• Perform CO/CO₂ ratio tuning.

Cause 2: Blocked Condensate Trap

Condensate traps can clog, causing inefficient operation and lockouts.

How to Fix a Blocked Condensate Trap

• Flush the trap and pipework.
• Re-route poorly installed external condensate runs.
• Install frost protection if needed.

4. Carbon Monoxide Risks

A boiler not serviced every year may leak carbon monoxide due to poor combustion or damaged seals, posing a life-threatening risk.

Cause 1: Deteriorated Seals or Gaskets

Over time, seals around the burner door and heat exchanger degrade.

How to Fix CO Leak Risks

• Replace seals and pressure-test the combustion chamber.
• Conduct a full flue gas analysis.
• Inspect flue integrity and joints.

Cause 2: Faulty Flue or Blocked Flue Terminal

Bird nests, debris, or flue disconnection can cause CO spillage.

How to Fix Flue Problems

• Remove obstructions from the flue terminal.
• Re-secure any loose flue sections.
• Install a flue guard to prevent future nesting.

5. Voided Boiler Warranty or Guarantee

A boiler not serviced every year violates the conditions of nearly all manufacturer warranties in the UK.

Cause: Missing Annual Service Record

Failure to produce an annual service log voids the warranty.

How to Fix Warranty Issues

• Arrange a service immediately.
• Request a service log and benchmark form.
• Some manufacturers allow warranty reinstatement if you can prove regular maintenance otherwise.

6. Illegal for Landlords (Gas Safety Non-Compliance)

A boiler not serviced every year puts landlords in breach of UK Gas Safety (Installation and Use) Regulations 1998.

Cause: No Valid CP12 Gas Safety Certificate

Landlords must complete annual safety checks.

How to Fix Compliance Issues

• Book a Gas Safe inspection immediately.
• Keep records for at least 2 years.
• Provide a copy to tenants within 28 days.

7. Shortened Boiler Lifespan

A boiler not serviced every year will wear out more quickly, often reducing lifespan by 3–5 years.

Cause 1: Overheating

Limescale, sludge, and blocked heat exchangers cause repeated overheating.

How to Fix Overheating Issues

• Powerflush or chemically clean the heating system.
• Replace or reset the overheat thermostat.
• Install a magnetic filter.

Cause 2: Corrosion in the System

Sludge and iron oxide build-up due to untreated water.

How to Fix Corrosion

• Perform a full system flush.
• Dose system with corrosion inhibitor.
• Fit a magnetic filter for long-term protection.

FAQs

Can skipping one annual service damage a new boiler?

Yes. Even modern condensing boilers rely on annual combustion checks and cleaning to prevent early wear. A single missed service can affect warranty and long-term health.

How much does a boiler service cost in the UK?

Typically £70–£120, depending on region and boiler type. This is far cheaper than the average breakdown repair, which ranges from £150–£600.

Do I need to service my boiler if it seems to be working fine?

Absolutely. Many internal issues show no symptoms until severe damage occurs.

How long does a boiler service take?

Usually 30–60 minutes, depending on how accessible the boiler is and whether issues are found.

Can I check anything myself before booking a service?

You can check pressure, radiators, and thermostat settings, but never open the casing—this is legally restricted to Gas Safe engineers.

Stay warm, The Boilers2Go Team