Method Statement for Boiler Installation — UK
A free, Gas Safe-aligned method statement for UK domestic and commercial boiler installation — covering isolation, decommissioning, flue routing, condensate, commissioning to BS 7593 and the customer handover paperwork inspectors actually ask for.
UK (RAMS) example document — Two-Storey Rear Extension — 14 Birchwood Lane, Reading. Client: Mr & Mrs A. Whitfield (Private Client). Site: 14 Birchwood Lane, Reading, RG1 5JT. Scope: Construction of a two-storey rear extension (6.4m × 4.2m) to an existing semi-detached dwelling. Works comprise breaking out of existing rear elevation, trench-fill foundations to 1.0m, traditional cavity blockwork to first floor, pre-stressed concrete lintels, timber roof structure with natural slate finish, plus alterations to existing rear wall to form structural opening with rolled steel joist (RSJ 203×102 UB23). Works programmed over 9 weeks with a peak site team of 6 operatives. Hazards assessed: Manual handling — blocks, lintels, plasterboard, Working at height — independent scaffold & roof structure, Buried services strike during excavation, Collapse of excavation / trench wall, Hand-arm vibration (HAVS) — breaking out, drilling, Silica dust — cutting blocks, brick, concrete, Vehicle/pedestrian segregation — narrow domestic street.
Full version
Preview first. No card needed. Download when you're happy.
- Site-specific draft
- Boiler Installation hazards baked in
- Ready for competent-person review
Built around recognised UK method statement structure — hazards, controls, sequence, PPE and sign-off. Ready for competent-person review.
Boiler installation is the work most often blamed in domestic carbon monoxide fatalities — 16 deaths in the UK in 2023, almost all traced to flue routing, combustion-air starvation or incorrect commissioning. Gas Safe Register's annual prosecutions list (most recently a Surrey engineer struck off and fined £24,000 in 2024 for a fatal CO incident traced to a blocked condensate-trap-derived flue gas recirculation) reinforces the same root cause every year: corners cut on the commissioning paperwork. This page sets out what a defensible UK boiler installation method statement looks like in 2026 — domestic combi swaps through to commercial cascaded systems — with a free editable template.
When is it required?
Any boiler installation must be carried out by a Gas Safe-registered engineer (Gas Safe (Installation and Use) Regulations 1998 reg. 3). On any commercial site under CDM 2015 a written MS is required before the engineer mobilises, alongside the engineer's Gas Safe card, the appliance-specific ACS qualification (e.g. CCN1 + CENWAT for domestic combi, ICPN1 for commercial), the manufacturer's installation guide, the unvented hot water certificate (G3) where applicable, and the COSHH assessment for any inhibitor, biocide or leak-detection fluid. For a domestic swap, the MS is the cleanest way to evidence Approved Document J (combustion appliances), Approved Document L (efficiency) and the Boiler Plus 2018 requirement.
What a good one looks like
A defensible boiler installation MS runs to 6–10 pages and names every specific. It identifies the appliance (e.g. 'Worcester Greenstar 8000 Style 30kW combi, 91.0% ErP'), the flue (concentric 60/100, route, terminal clearances per BS 5440-1), the gas pipework upgrade (Boiler Plus may require 28mm from meter), the condensate disposal route (internal preferred — BS 6798), the inhibitor (e.g. 'Sentinel X100, 1L per 100L system volume') and the commissioning check (BS 7593:2019). It cross-references the manufacturer's install guide, the benchmark log book and the Building Regulations notification. It is signed by the Gas Safe engineer who will do the install — not a manager.
Boiler Installation hazards & controls
The site-specific hazards a boiler installation MS must address, with the controls that take residual risk to an acceptable level.
| Hazard | Persons at risk | Controls | Residual |
|---|---|---|---|
| Carbon monoxide — flue gas spillage or recirculation | Occupants, engineer | Flue route per BS 5440-1 with all terminal clearances respected; smoke test or flue gas analyser at commissioning; CO alarm fitted in room with appliance (Building Regs requirement on installation); engineer's flue gas analyser within calibration (annual cert) | Low |
| Gas leak during work or post-install | Occupants, engineer | Isolation at meter with tagging; tightness test before lighting per IGEM/UP/1B; manometer in working order; leak-detection fluid (no aerosol naked-flame test) at every joint; let-by test on the existing pipework; post-install tightness test signed in benchmark log | Low |
| Electric shock during electrical connection / isolation | Engineer | Safe isolation at consumer unit with proving unit (e.g. Martindale VI13800); LOTO padlock on the MCB; voltage absence proven before work; re-energisation only after RCD test; engineer holds 18th Edition wiring or equivalent for the isolation work; commercial work signed by 18th Edition electrician separately | Low |
| Asbestos in pre-2000 flue boxes, boiler casings, AIB cupboards | Engineer, occupants | R&D survey for any pre-2000 commercial installation; visual check of existing flue and casing in domestic; if suspected — stop, sample, do not disturb; licensed contractor for AIB removal; engineer trained in asbestos awareness (UKATA) | Medium |
| Manual handling — boilers 30–60 kg, cylinders 50–100 kg | Engineer, mate | Two-person lift mandatory >25 kg; stair-climbing trolley for cylinders; pre-route checked for clearance and weight-bearing; no single-handed lift onto a wall mount — second person spots and stabilises | Medium |
| Hot works — soldering, brazing | Engineer, occupants | Hot works permit on commercial; heat shield behind every joint; CO2 + water extinguisher within 5m; combustibles cleared within 1m; 30-minute fire watch after last flame; push-fit (Speedfit, JG, Tectite) used wherever practicable instead of solder | Low |
| Legionella in new or stagnant systems | Occupants, especially immunocompromised | Flush system before commissioning per BS 7593:2019; thermostatic mixing valves to 60°C cylinder / 55°C tap; commission unvented HW per G3; written scheme of control on commercial per HSG274 part 2 | Low |
| COSHH — inhibitor, biocide, leak-detection fluid, flux | Engineer, occupants | COSHH sheet on van for every product; nitrile gloves; eye protection during inhibitor dosing; eye-wash bottle on van; spill cloth; no flux on potable water joints | Low |
Step-by-step sequence
- 1
1. Pre-installation survey & briefing
Gas Safe engineer reviews flue route, gas pipe size (Boiler Plus 2018 may require upgrade), electrical supply, condensate route. Survey signed off, customer briefed, MS issued to customer for any occupied install. Card photographed to job file.
- 2
2. Isolation & decommissioning
Gas isolated at meter with tagging. Electrical isolation at consumer unit with proving unit and LOTO. Water isolated at stop tap and drained from the system. Existing appliance disconnected. Old boiler removed per WEEE.
- 3
3. Flue & combustion air check
Flue route confirmed against BS 5440-1 — terminal clearances from openings, boundaries and ground. Combustion air provision checked. Any new wall penetration sealed and made good.
- 4
4. Pipework & gas connection
Gas pipe upsized where Boiler Plus or appliance gas rate requires (typical 28mm from meter for 30kW+ combi). Push-fit or compression on water; copper or stainless on gas. Tightness test per IGEM/UP/1B on completion.
- 5
5. Electrical connection
Fused spur or appliance-rated isolator within 1m of boiler. Earth continuity tested. RCD test on the supply circuit. Commissioned via the OEM lead, not a re-purposed flex.
- 6
6. System fill, dose & commission
System flushed per BS 7593:2019 (chemical and mechanical for cast-iron or sludged systems). Inhibitor dosed per manufacturer (typical 1L per 100L water volume). Filter installed in return per Boiler Plus. Pressurised, vented, leak-checked.
- 7
7. Combustion analysis, benchmark & handover
Calibrated flue gas analyser used at low and high fire — combustion ratio and CO/CO2 logged in the benchmark book. Customer briefed on operation, condensate, frost protection. Notified to Building Control via Gas Safe within 30 days. MS, benchmark, warranty bundled to the customer file.
30kW combi swap, 1980s 3-bed semi, removal of an old open-flue back boiler
A Greater London Gas Safe engineer working on a 30kW combi swap (replacing a 1980s open-flue back boiler in a 3-bed semi) produced a 8-page MS that the customer's home insurer accepted as evidence for warranty continuity. Key entries: a Worcester Greenstar 8000 Style 30kW (91.0% ErP) replacing a Baxi back boiler; gas pipe upgraded to 28mm from the meter for the first 4m to satisfy the Boiler Plus 2018 gas rate calculation; concentric 60/100 flue terminating 2.5m from the nearest opening window (BS 5440-1 requires 600mm minimum, so well clear); system pre-flushed mechanically with a Sentinel JetFlush 4 after the back boiler was decommissioned, then dosed with 1L Sentinel X100 inhibitor; a Magnaclean Professional2 XP filter fitted on the return per Boiler Plus filter requirement; combustion analysis at low and high fire logged in the benchmark (CO/CO2 ratio 0.0004 at high fire, well within the manufacturer's 0.004 limit); a Honeywell CO alarm fitted in the kitchen per Approved Document J. Notified to Building Control via Gas Safe portal on day of install. Customer briefed on operation, condensate trap and annual service. 1-day install, zero call-backs, 10-year manufacturer warranty registered. The MS, the benchmark book and the Gas Safe certificate were the three documents that closed the job out.
Or build a site-specific boiler installation MS in 5 minutes
The free template is a blank Word document. The Riskora builder ships with the boiler installation hazard library baked in — pick the preset, edit the site-specific bits, download a signed PDF.
Common mistakes that get a boiler installation MS rejected
- ·Routing the flue past an opening window or under an eaves overhang inside the BS 5440-1 clearance — the single most common cause of CO recirculation
- ·Forgetting the system flush and inhibitor — the warranty void clause every manufacturer enforces
- ·Not upsizing the gas pipe on a Boiler Plus-compliant high-output combi (28mm from meter for 30kW+ is the typical requirement)
- ·Failing to fit the CO alarm required by Approved Document J at the same visit — and not noting it in the benchmark book
- ·Soldering on a live water system without a hot works permit on commercial — a 2023 prosecution of a Liverpool contractor turned on exactly this after a sprinkler activation
- ·Notifying Building Control late or not at all — Gas Safe's portal records the notification, but the engineer is the one who is fined when it's missed
Frequently asked questions
Do I need an MS for a domestic boiler swap?
Legally a documented procedure isn't required for a single dwelling under sole occupation, but Gas Safe's competent person scheme conditions and most manufacturer warranties expect one. An MS is also the cleanest way to evidence Approved Document J (combustion appliances), Approved Document L (efficiency) and Boiler Plus 2018 compliance.
What's the Boiler Plus 2018 requirement?
All gas combi boilers installed in England from April 2018 must have ErP ≥92% efficiency and at least one of: load compensation, weather compensation, smart controls (e.g. Hive Active), or flue gas heat recovery. The MS must name which control is fitted and reference the relevant manufacturer datasheet.
When does the gas pipe need upsizing?
When the calculated gas rate at the appliance, accounting for length and fittings, drops the inlet pressure below the manufacturer's minimum (typically 17–20 mbar working). For a 30kW+ combi on a long run, this almost always requires 28mm from the meter — the calculation must be in the MS, not assumed.
Do I have to fit a CO alarm?
Yes — Approved Document J (and equivalent in Scotland, Wales, NI) requires a CO alarm in the room with any new or replacement combustion appliance. The alarm must comply with BS EN 50291, be wall-mounted at the correct height and noted in the benchmark book.
Who notifies Building Control?
The Gas Safe engineer, via the Gas Safe portal, within 30 days of completion. The customer receives a Building Regulations Compliance Certificate by post. This is non-delegable — the engineer is the one fined if it's missed.
Related method statements & RAMS
Download the template, or build it in 5 minutes
Riskora is an assistive document preparation tool. Every method statement must be reviewed and signed by a competent person before use.