Commercial Boiler Servicing London: CP17, Tightness Tests & Compliance Explained

BlueFlame Plumbing & Heating · Gas Safe 633735 · ~10 min read

Commercial boiler servicing involves safety checks and maintenance of gas-fired equipment in non-domestic premises. The legal duties come primarily from the Gas Safety (Installation and Use) Regulations 1998, alongside wider workplace health and safety obligations. The responsible duty holder — the business owner, landlord, or facilities manager — must ensure suitable inspection, maintenance, and records are in place. This guide explains what commercial servicing covers, the certificate types involved, and when each one applies.

Why commercial gas is different from domestic

The mechanics of combustion are the same. The legal context, the engineer qualifications, and the documentation are different. Three things make commercial work distinct:

1. The engineer needs the right qualifications

Every gas engineer in the UK is registered with Gas Safe Register, and registration is broken into categories — domestic, non-domestic, catering, LPG, and so on. The engineer must be qualified and registered for the type of work and appliance involved. Always check the engineer’s Gas Safe ID card and confirm their categories cover the work you need. The Register itself is searchable by name or registration number at gassaferegister.co.uk.

2. The duty holder is responsible for compliance

Under the Gas Safety (Installation and Use) Regulations 1998 and wider health and safety law, a “duty holder” — the owner, landlord, employer or facilities manager — is responsible for ensuring the gas safety of the premises. Failure to comply can expose the responsible duty holder and organisation to enforcement action by the HSE or local authority, including fines, improvement notices, and in serious cases prosecution.

3. The work is more rigorous

Commercial systems usually mean larger appliances, larger gas pipes, more complex flue routing, and higher pressures. The standards (including IGEM/UP/1A and the GSIUR) require additional testing — strength testing, tightness testing, gas purging — that doesn’t apply to a typical domestic combi. The paperwork is heavier and the engineer’s scope must be matched correctly to the installation.

The legal landscape

Three pieces of legislation drive the requirement:

For landlords specifically, the GSIUR requires a written record of an annual gas safety check on every gas appliance in any rental property — issued by a Gas Safe registered engineer, kept on file for two years, and provided to tenants within 28 days of the inspection.

CP12, CP17, CP15 and TPCP1 explained

The acronyms are confusing because they were designed for engineers, not customers. Here’s what each one is, with the caveat that the actual documentation and test method depend on the installation and the engineer’s scope:

For most South London businesses we work with, the live questions are usually:

• CP12 or CP17? If anyone lives in the property — even an HMO with a shared kitchen — it’s CP12. If it’s purely commercial use, CP17. Mixed-use buildings with flats above shops typically need both.
• What about a pub kitchen? Pub bar and dining areas usually fall under CP17. The catering kitchen needs CP15 — and a different engineer if your CP17 engineer doesn’t hold catering qualifications.
• Do I need TPCP1? Possibly — TPCP1 procedures are used for certain tightness testing and purging scenarios, particularly on larger commercial installations. Your engineer will tell you on inspection whether it applies.

Using the wrong certificate can mean the record doesn’t satisfy the compliance requirement you were trying to meet, so it’s worth checking with the engineer before booking.

What a commercial boiler service typically covers

A non-domestic gas service follows the relevant IGEM standards and the manufacturer’s service schedule. Specific steps vary by boiler type, manufacturer, and installation — not every appliance gets the same checks. On a typical commercial gas-fired boiler, a thorough service will usually include:

• Documentation review — installation records, previous service certificates, gas pipe diagram (where available)
• External inspection — boiler, flue, gas supply pipework, ventilation provision, isolation valves
• Tightness test at the meter — recorded with a calibrated manometer, following the relevant procedure
• Standing and working pressure verification at the appliance
• Combustion analysis — flue gases sampled with a calibrated FGA, ratios recorded, comparison to manufacturer specification
• Burner inspection — fouling, fan operation, ignition sequence checked
• Heat exchanger — visual inspection where access permits, indicators of corrosion or scaling noted
• Flue inspection — flue gas spillage test, condition of terminal, drainage of condensate
• Safety device function test — overheat thermostat, flame failure cutoff, low water cutoff (where fitted)
• Ventilation provision — minimum free area calculation, vent grilles unobstructed
• System pressure — operating pressure recorded, expansion vessel pre-charge tested
• Pump & controls — circulation pump operation, thermostat calibration
• Magnetic filter — cleaned and contents inspected, where fitted
• CP17 issued — full report, defects classified by severity (Immediately Dangerous, At Risk, Not To Current Standards), distributed to the duty holder

For larger installations, anything with non-standard pipework, or after work that breaks gas continuity, additional tightness testing and purging following TPCP1 / TPCP1A procedures may be required. We charge this separately and quote on inspection.

Service requirements by property type

Different premises have different documentation needs. The principle is the same — annual safety check, records kept on file — but the certificates and depth vary.

Pubs and licensed premises

Bar and dining areas: CP17 annually. Catering kitchen: separate CP15 from a catering-qualified engineer. Cellar gas (where used for keg cooling, rare): CP17. Insurance often requires a current copy on file — check your policy.

Offices and retail

CP17 covering the boiler and any gas water heaters. Where the building has multiple commercial tenants, the freeholder usually carries the responsibility for the central plant; tenants are typically responsible for any gas-fired equipment they install themselves. Check the lease.

Shops with residential flats above (mixed use)

Common in South London. The shop generally needs CP17, the flats need CP12 (one per let unit). If the gas supply is shared, both certificates may be issued by the same engineer in a single visit, depending on the installation.

HMOs (Houses in Multiple Occupation)

Treated as residential lets — CP12 required annually. HMOs with five or more occupants and shared facilities are also subject to additional licensing requirements under the Housing Act, with the local authority typically asking for a copy of the current gas safety record.

Schools, places of worship, community buildings

CP17 annually. The duty holder is usually a named trustee, governor, or facilities manager. Charity-run premises are not exempt from the gas safety regulations.

Light industrial / small workshops

CP17 for the heating boiler. Where gas is used in any process equipment (drying ovens, small kilns), additional process safety assessments may apply. Our scope here is conventional space heating.

How often a commercial boiler should be serviced

Annually as the regulatory minimum for the safety check element. Twice yearly is good practice for any installation where downtime is genuinely costly — pubs, restaurants, care homes, schools running heating through the winter term. The second visit doesn’t need to be a full service; an interim check halfway through the year can catch the issues that lead to mid-winter failures.

Your insurer may have its own requirements. Many commercial buildings policies are written with a “maintain to manufacturer’s recommendation” clause, which on most modern commercial boilers means annual servicing. If you’re not sure what your policy says, ask your broker.

Time of year matters. Late summer is the right window — September is ideal. The boiler has been resting through the warm months, defects can be addressed before the heating season starts, and engineer availability is at its best.

What we do — and what we don’t

BlueFlame’s commercial scope is deliberate. We do focused work well rather than spreading thin across every commercial gas category.

What we do

• Commercial boiler servicing up to 70kW single boiler
• CP17 Non-Domestic Gas Safety Records
• CP12 Landlord Gas Safety Records — single properties or portfolios
• TPCP1 / TPCP1A tightness testing and purging on commercial installations within scope
• Small commercial boiler installation and replacement
• Sub-contracted second-engineer work for other firms (purging, tightness testing)
• Mixed-use buildings (commercial + residential) under one visit where practical

What we don’t do

• Commercial catering gas (CP15) — restaurant kitchens, fryers, ranges
• Multi-boiler cascade plant rooms — anything beyond a single appliance
• Industrial gas — process gas, large kilns, drying equipment, district heating
• LPG installations
• 24/7 commercial on-call cover (we offer same-day response in normal hours)

If your work falls outside our scope, we’ll say so on the first call rather than waste your time. We can usually point you toward a trusted specialist who handles what we don’t.

Commercial boiler service FAQ

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