Risk Assessments · Mandatory · Pre-Construction

RAMS — Mechanical and Plumbing Works

This RAMS covers the installation of mechanical services including heating, ventilation, air conditioning, and plumbing systems. It addresses manual handling of heavy components, working at height in risers, hot works during pipework jointing, and commissioning of pressurised systems. Coordination with other trades is essential to manage interface risks.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. MHSWR 1999 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

RAMS category	B10 Mechanical & Plumbing
Gas legislation	Gas Safety (Installation and Use) Regulations 1998 — all gas work must be carried out by a Gas Safe registered engineer
Water regulations	Water Supply (Water Fittings) Regulations 1999 — mandatory notification for specified categories of water work
Legionella	L8 ACoP (Approved Code of Practice) — Legionnaires’ disease: the control of legionella bacteria in water systems (HSE, 4th Ed.)
Refrigerant gases	F-Gas Regulation (EU 517/2014, retained UK law) — handling of fluorinated greenhouse gases requires certification
Competence standard	Gas Safe Register; NVQ Level 2/3 Plumbing & Heating; REFCOM/F-Gas certification; BPEC or equivalent for unvented hot water
Enforcing authority	HSE (gas safety, workplace H&S); local water undertaker (water regulations); Environment Agency (F-Gas)

1. What It Covers

A RAMS for Mechanical and Plumbing works covers the installation, alteration, maintenance, and commissioning of all building services that involve the movement of water, gas, refrigerant, or air. This includes domestic hot and cold water systems, heating and boiler installations, gas pipework and appliance installation, sanitary pipework and drainage above ground, HVAC (heating, ventilation, and air conditioning) systems, chilled water systems, refrigeration plant, sprinkler and fire suppression systems, and the testing and commissioning of all mechanical services.

The hazard profile of mechanical and plumbing work is broad. It spans life-critical risks — gas explosions, carbon monoxide poisoning, legionella — alongside everyday construction hazards such as working at height, manual handling, and COSHH exposure. The regulatory framework is correspondingly wide, drawing on the Gas Safety (Installation and Use) Regulations 1998, the Water Supply (Water Fittings) Regulations 1999, the L8 Approved Code of Practice for legionella control, and the F-Gas Regulation for refrigerant handling.

Every RAMS for mechanical and plumbing work must identify the specific systems being installed, the substances involved (gas, water, refrigerant, flux, solder, jointing compounds), the interfaces with other trades (electrical, structural, fire), and the testing and commissioning procedures that will confirm the installation is safe before handover.

Gas work is non-negotiable — Gas Safe or nothing

It is a criminal offence under the Gas Safety (Installation and Use) Regulations 1998 for anyone to carry out gas work unless they are registered with Gas Safe Register (or are employed by a Gas Safe registered business and work under their supervision). This includes installation, maintenance, repair, disconnection, and purging of gas pipework and appliances. There are no exceptions for ‘simple’ gas tasks. An unregistered person who works on a gas installation commits an offence punishable by an unlimited fine and up to two years' imprisonment.

2. Key Hazards

The following table identifies the principal hazards associated with mechanical and plumbing works on construction sites, who is at risk, the contributing risk factors, and the controls that must be addressed in the RAMS.

Hazard	Who at risk	Risk factors	Controls
Gas leak and explosion	All site personnel; adjacent occupants; emergency responders	Incorrectly jointed gas pipework; damage to existing gas mains during groundworks; incomplete purging; failure to tightness-test before commissioning	Gas Safe registered engineer for all gas work; tightness testing (let-by and working pressure) before energisation; purging procedures to IGE/UP/1B; gas detection equipment on site; emergency isolation valve identified and accessible; no hot works permit issued until gas system confirmed safe
Carbon monoxide (CO) poisoning	Operatives working near gas appliances; building occupants post-handover	Incomplete combustion from poorly installed or commissioned boilers, water heaters, or warm air units; blocked flues; inadequate ventilation	Combustion performance analysis on all gas appliances at commissioning; flue integrity testing; ventilation calculations to BS 5440; CO alarm installation; Gas Safe registered engineer to commission and certify all gas appliances
Scalding from hot water	Plumbers during testing and commissioning; building occupants post-handover	Unvented hot water systems operating at high temperature and pressure; thermostatic mixing valves not set or not installed; blending valve failure	Unvented hot water installation by BPEC-qualified (or equivalent) installer; TMV commissioning to confirm outlet temperatures within safe limits (max 48 degrees Celsius for healthcare, 44 degrees Celsius for baths in care settings); pressure and temperature relief valve tested at commissioning
Legionella (Legionnaires’ disease)	All building occupants; maintenance personnel; anyone exposed to water aerosols from the building systems	Water stagnation in dead legs, infrequently used outlets, and storage vessels; water temperature between 20 and 45 degrees Celsius; biofilm accumulation; inadequate system design allowing low-flow zones	System design to minimise dead legs and stagnation points; hot water stored at 60 degrees Celsius minimum, distributed at 50 degrees Celsius minimum; cold water below 20 degrees Celsius; pre-commission flush of all pipework; written legionella risk assessment to L8 ACoP; water hygiene management plan for the completed installation
Water regulations non-compliance	Building owner (legal liability); water supply undertaker; downstream properties at risk of contamination	Cross-connection between wholesome and non-wholesome supplies; backflow from heating circuits into drinking water; incorrect use of non-approved fittings; failure to notify notifiable work	All fittings to comply with Water Supply (Water Fittings) Regulations 1999; WRAS-approved products used throughout; backflow prevention devices installed to the appropriate fluid category; notification to local water undertaker for notifiable categories of work (see table below)
Working at height	Plumbers and HVAC installers working on pipework, ductwork, and plant at ceiling level and in risers	Extended overhead work from ladders; work in vertical risers without adequate platforms; access to rooftop plant without edge protection	WAH hierarchy applied (avoid, prevent, minimise); tower scaffold or MEWP for overhead pipework and ductwork installation; fixed platforms in risers; edge protection on flat roofs when accessing plant; PASMA or IPAF training as appropriate
Manual handling	Plumbers, pipefitters, and HVAC installers handling boilers, cylinders, radiators, ductwork sections, pipe lengths, and plant equipment	Heavy items (boilers up to 100 kg, cylinders, cast iron radiators); awkward access routes (stairwells, risers, ceiling voids); repetitive carrying and positioning	Mechanical handling for items above 25 kg (hoists, trolleys, pipe carriers); team lifts for intermediate loads; delivery to point of installation where possible; manual handling assessment for all tasks involving heavy or awkward loads
COSHH (flux, solder, adhesives, jointing compounds)	Plumbers and pipefitters using soldering, brazing, and chemical jointing methods	Lead-free solder flux fumes; brazing fumes in poorly ventilated spaces; solvent-based adhesives for plastic pipework; skin contact with flux and cleaning agents	COSHH assessment for all substances used; LEV (local exhaust ventilation) or adequate natural ventilation for soldering and brazing; RPE where ventilation is insufficient; correct PPE (gloves, eye protection); material safety data sheets available on site; lead-free solder mandatory for drinking water systems
Water damage from system failure during testing	All trades and building fabric; electrical installations at risk of water ingress	Pressure testing revealing joint failure; burst during commissioning; incorrect pressure applied; failure to isolate completed sections before test	Pressure testing to BS EN 806 or manufacturer specification; test area isolated and clearly marked; other trades notified before pressure testing; absorbent materials and drainage available; electrical installations protected or isolated in test zones; competent person supervising all pressure tests

3. Water Regulations — Notifiable Work

The Water Supply (Water Fittings) Regulations 1999 require that certain categories of plumbing work are notified to the local water undertaker before work begins. Failure to notify is a criminal offence and can result in the water undertaker requiring the work to be exposed for inspection or even disconnecting the supply. The following table sets out the categories of work that require notification.

Category of notifiable work	Examples and notes
Erection of a new building or extension	All new plumbing installations in new buildings or extensions require notification, regardless of size or complexity.
Installation of a bidet with ascending spray	Bidets with ascending spray or flexible hose create a fluid category 5 backflow risk and must be notified.
Installation of a bath or shower exceeding 230 litres capacity	Large-volume baths and shower installations that may affect supply pressure to neighbouring properties.
Installation of a water softener or other treatment equipment	Any device connected to the mains supply that treats or conditions the water, including water softeners, filters, and dosing systems.
Installation of a garden watering system (other than hand-held hose)	Fixed irrigation systems, sprinkler systems, and any below-ground garden watering installation.
Installation of a reduced-pressure zone (RPZ) valve or other backflow prevention device for fluid category 4 or 5	RPZ valves and other high-category backflow prevention devices installed to protect against contamination of the mains supply.
Construction of a pond or swimming pool with auto-fill from mains	Any pond, swimming pool, or water feature with a direct or indirect mains supply connection.
Installation of any water fitting in premises used for non-domestic purposes (commercial, industrial, agricultural)	All plumbing installations in non-domestic premises require notification, including offices, factories, farms, and commercial buildings.

Notification must be given before work starts — not after

The Water Supply (Water Fittings) Regulations 1999 require that the water undertaker is notified at least 10 working days before notifiable work begins. The water undertaker has the right to inspect the work and may withhold consent until they are satisfied that the installation will comply with the regulations. Starting work before notification — or before the 10-day notice period has elapsed — is an offence. The water undertaker also has the power to disconnect the supply to any premises where non-compliant fittings are installed.

4. Competence

Mechanical and plumbing work spans multiple disciplines, each with distinct competence requirements. The RAMS must specify the qualifications and registrations required for every element of the work. The principal contractor must verify these before any operative begins work.

Discipline	Required qualification / registration	Notes
Gas installation and maintenance	Gas Safe Register (individual registration with relevant ACS categories)	Every individual carrying out gas work must be registered with Gas Safe and hold the specific ACS (Accredited Certification Scheme) categories for the type of gas work being carried out (e.g. CCN1, CENWAT, CKR1 for domestic; CMDDA1, ICPN1 for commercial). Registration must be current and the categories must match the work scope.
Plumbing (general)	NVQ Level 2 or 3 in Plumbing and Heating; CSCS or JIB-PMES card	General plumbing operatives should hold a relevant NVQ and a CSCS card at the appropriate level. For unvented hot water systems, a separate BPEC (or equivalent) qualification is required. The CSCS card confirms the individual has been assessed for their specific occupation.
HVAC and refrigeration	REFCOM Elite or REFCOM membership; F-Gas Category I or II certification	Any person handling fluorinated refrigerant gases must hold a personal F-Gas certificate (Category I for all activities, Category II for recovery only). The employing company must be registered with REFCOM or an equivalent F-Gas certification body. Non-certified handling of F-Gas refrigerants is a criminal offence.
Pressure testing	Competent person trained in pressure testing procedures to BS EN 806 or relevant standard	Pressure testing of water systems, gas installations, and HVAC systems must be carried out by a competent person who understands the test parameters, the failure modes, and the safety precautions required. Pressure testing is a high-energy activity — a burst joint under test pressure can cause injury.
Legionella risk assessment	City & Guilds accredited legionella risk assessor qualification (or equivalent); membership of the Legionella Control Association (LCA) preferred	The L8 ACoP requires that legionella risk assessments are carried out by a competent person. For complex systems, this should be a specialist assessor with formal training. For simpler systems, a competent plumber with legionella awareness training may suffice, but the assessment must still be documented and meet L8 requirements.

Gas Safe categories are work-specific — not blanket

A Gas Safe registration is not a single qualification. It is a set of individual ACS (Accredited Certification Scheme) categories, each covering a specific type of gas work on a specific appliance type. An engineer registered for domestic boiler installation (CENWAT) is not automatically qualified for commercial catering gas (CMDDA1) or LPG installations. The RAMS must specify the ACS categories required for the gas work on the project, and the principal contractor must verify that each engineer holds the relevant categories on their Gas Safe ID card.

5. Common Mistakes

Allowing non-Gas Safe registered operatives to carry out gas work

It is a criminal offence for anyone not registered with Gas Safe to carry out any gas work. This includes seemingly minor tasks such as disconnecting a gas cooker, capping a gas supply, or reconnecting a meter. The RAMS must specify that all gas work is restricted to named Gas Safe registered engineers with the correct ACS categories. No exceptions, no supervision-only arrangements for unregistered individuals.

Omitting legionella risk from the RAMS for domestic hot and cold water installations

Legionella is not confined to cooling towers and large commercial systems. Domestic-scale hot and cold water systems in new-build and refurbishment projects can harbour legionella if the design or installation allows stagnation, dead legs, or temperatures in the 20 to 45 degree Celsius growth range. The RAMS must address legionella risk for all water system installations, not just large mechanical plant.

Failing to notify the water undertaker for notifiable plumbing work

The Water Supply (Water Fittings) Regulations 1999 require notification to the local water undertaker at least 10 working days before commencing notifiable categories of work. All plumbing in non-domestic premises is notifiable. Failure to notify is an offence. The water undertaker can require the work to be uncovered for inspection and can disconnect the supply for non-compliance.

Not carrying out a pressure test before concealing pipework

Pipework that is concealed in walls, floors, or ceilings without being pressure tested first creates a significant risk of undetected leaks causing water damage, structural damage, and electrical hazards. The RAMS must require pressure testing of all pipework before it is concealed. Test results must be recorded and signed off by the person carrying out the test.

Using non-WRAS approved fittings on drinking water systems

The Water Supply (Water Fittings) Regulations 1999 require that all fittings in contact with drinking water comply with the regulations. Using WRAS (Water Regulations Advisory Scheme) approved products is the simplest way to demonstrate compliance. Non-approved fittings may leach contaminants or fail to provide adequate backflow protection. The RAMS should specify WRAS-approved materials throughout.

Failing to specify F-Gas certification for refrigerant handling

Handling fluorinated greenhouse gases (HFCs, HFOs) without personal F-Gas certification is a criminal offence under the retained EU F-Gas Regulation. This applies to installation, maintenance, servicing, repair, and decommissioning of refrigeration and air conditioning equipment containing F-Gas refrigerants. The RAMS must require F-Gas Category I or II certification for every operative handling refrigerant, and the employing company must hold REFCOM or equivalent registration.

6. Frequently Asked Questions

Can a plumber who is not Gas Safe registered work on the water side of a combi boiler?▾

No. Any work on a gas appliance — including the water connections to a gas boiler — is classified as gas work under the Gas Safety (Installation and Use) Regulations 1998. Only a Gas Safe registered engineer with the relevant ACS category (CENWAT for domestic central heating wet) may carry out this work. A plumber without Gas Safe registration cannot work on any part of a gas appliance, even if the gas supply is isolated.

What temperature should hot water be stored at to control legionella?▾

The L8 Approved Code of Practice requires that hot water is stored at a minimum of 60 degrees Celsius and distributed at a minimum of 50 degrees Celsius (measured at the return leg of a circulating system, or at the outlet nearest the cylinder on a non-circulating system). These temperatures are sufficient to kill legionella bacteria. At the same time, thermostatic mixing valves must be installed at point of use to prevent scalding — the storage temperature requirement and the scalding prevention requirement must both be met.

Is pressure testing of heating pipework required by regulation?▾

Yes. BS EN 14336 requires pressure testing of all heating systems before commissioning. In practice, pressure testing is required by Building Regulations Approved Document L (conservation of fuel and power), as an untested system cannot be confirmed as leak-free. The test pressure, hold time, and acceptance criteria are defined in the relevant standard and must be recorded. For gas-fired systems, the gas pipework tightness test is a separate requirement under Gas Safe procedures.

What is a fluid category and why does it matter for backflow prevention?▾

The Water Supply (Water Fittings) Regulations 1999 classify water into five fluid categories based on contamination risk, from category 1 (wholesome drinking water) to category 5 (water containing serious health hazards including pathogens and toxic substances). The fluid category determines the type of backflow prevention device required at each connection point. For example, a mains connection to a heating system (category 3) requires a different level of protection than a connection to a chemical dosing tank (category 5). Incorrect fluid category assessment is one of the most common water regulations failures.

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