Annual Boiler Service Checklist for London Landlords — What to Expect

Why Landlords Should Understand What a Boiler Service Covers

Many London landlords book an annual boiler service — often combining it with the annual gas safety check — and simply receive a certificate without knowing what was actually done. Understanding the full checklist means you can verify the quality of the service and hold engineers accountable for the work you paid for.

Pre-Service Information to Provide

When the engineer arrives, tell them:

• Any fault codes the boiler has shown since last service
• Any recent changes — new radiators fitted, pressure loss events, changes to the heating zone configuration
• Whether tenants have reported any problems with heating or hot water response

The Full Service Checklist

Visual and External Checks

• Check flue terminal outside — free of obstruction, correct height from windows and doors, no signs of soot staining
• Inspect external gas pipework for corrosion
• Check the condensate pipe is clear and not sagging
• Check boiler casing for staining, corrosion, or physical damage

Internal Component Checks

• Remove burner assembly and inspect for deposits or damage
• Check and clean ignition electrodes — carbon tracking is a common cause of ignition faults
• Inspect the main heat exchanger for scale deposits, corrosion, or signs of leakage
• Check the diverter valve operation (combi boilers) — should switch cleanly between heating and hot water modes
• Check the pump operation — speed setting, noise level, and flow rate
• Check the expansion vessel pre-charge pressure — should be 0.75-1 bar when system is cold and depressurised
• Inspect the pressure relief valve — check it opens and reseals correctly
• Check all gas valve seals and connections

Combustion Analysis (Critical)

• Connect flue gas analyser to the flue sampling point
• Check CO₂ percentage (natural gas boiler: typically 8-9% at full load)
• Check CO/CO₂ ratio — should be below 0.004 for a safe, efficient burner
• Check gas rate at the gas valve against the boiler's nameplate specification

System Checks

• Check and record system pressure
• Test inhibitor concentration using a test strip or meter — should be within the manufacturer's recommended range
• Check magnetic filter (if fitted) — the filter should be cleaned at every service
• Check all visible pipework joints for signs of weeping

What the Service Report Should Include

After a proper service, the engineer should provide:

• Combustion analysis results (CO₂ %, CO/CO₂ ratio)
• Expansion vessel pre-charge pressure reading
• Inhibitor concentration result ("Pass" or reading)
• Notes on any observations requiring attention
• Service date, engineer name, Gas Safe number, and signature

If the report you receive has none of these readings — just a pass/fail certificate — ask the engineer to complete a full service report before paying.