Short answer: in a workplace, regulation 35 of the Gas Safety (Installation and Use) Regulations 1998 requires the employer to keep the boiler, pipework and flue safe, without setting an interval. Manufacturers set one: Ideal's Evomax manual says at least annually. After servicing, regulation 26(9) requires checks of the flue, combustion air, gas pressure or heat input, and safe operation.
What the law asks for
The Gas Safety (Installation and Use) Regulations 1998 (GSIUR) apply in England, Wales and Scotland. Northern Ireland has its own 2004 Regulations, which this guide does not cover. Four regulations shape a commercial boiler service:
| Regulation | What it says | Who it binds |
|---|---|---|
| Reg 35 | Any gas appliance, installation pipework or flue at a place of work under their control is "maintained in a safe condition so as to prevent risk of injury to any person" | The employer or self-employed person in control |
| Reg 3(1) and (3) | No one may work on a gas fitting unless competent, and employers and the self-employed may only do so as members of the class approved by HSE, which is the Gas Safe Register | The servicing business and its engineers |
| Reg 26(9) | After any work on a gas appliance, immediately examine the flue, the combustion air supply, the operating pressure or heat input (or, where that is not reasonably practicable, combustion performance), and its operation, then notify any defect | The engineer who did the work |
| Reg 34(3) | Anyone working on gas fittings who suspects an appliance is dangerous must take all reasonably practicable steps to tell the responsible person for the premises | The engineer |
"Work" in GSIUR includes "maintaining, servicing, permanently adjusting ... repairing" a gas fitting (reg 2(1)), so a service brings in regulation 26(9) every time. HSE tells employers to make sure gas appliances are maintained "by a competent person and in line with manufacturers' instructions and appropriate standards".
Factories, mines, quarries, agricultural premises, construction site huts and sewage works are mostly outside GSIUR, and general health and safety law applies there instead. Our guide to gas safety law in commercial premises explains where each duty applies, including boilers that also serve flats.
How often: the manufacturer decides
GSIUR sets no service interval for workplaces. The manufacturer's instructions do. As an example, Ideal's installation and servicing manual for the Evomax range (30 to 150 kW, UIN 206210 A17) says:
- the frequency of servicing "will depend upon the installation condition and usage but should be carried out at least annually";
- maintenance should "preferably be performed at the end of the heating season";
- removal and cleaning of the heat exchanger is recommended annually, and the heat exchanger, sump and condensate trap "must be inspected and cleaned after a maximum of 2 years operation";
- "it is the law that any service work must be carried out by a Gas Safe Registered Engineer".
Other makes set their own schedules. Always work from the manual for the model in front of you.
What to check on the visit
| Check | Legal basis | What the Ideal Evomax manual asks for |
|---|---|---|
| Boiler working before you start | Reg 26(9)(d), safe functioning | Light the boiler and carry out function checks, noting any operational faults |
| Gas rate | Reg 26(9)(c), operating pressure or heat input | Run for 5 minutes, then check the gas consumption rate; input of at least 90% of nominal |
| Combustion | Reg 26(9)(ca) where pressure or heat input cannot reasonably be checked | Flue gas analyser at the sampling point: CO/CO2 ratio not greater than 0.004, CO2 as in the manual's table, CO not over 350 ppm after servicing |
| Burner, heat exchanger, sump, condensate trap | Reg 35, safe condition | If the combustion check is not right: remove and clean the burner, inspect the heat exchanger and spray water down the flueways if there is aluminium oxide build-up, scrape out the sump, and flush the condensate trap |
| Flue | Reg 26(9)(a), effectiveness of the flue | Check the flue terminal is unobstructed and the flue system is sealed correctly |
| Combustion air and ventilation | Reg 26(9)(b), supply of combustion air | Refit the jacket front panel so it seals properly; HSE also asks employers to check rooms with gas appliances have adequate ventilation and not to block air inlets |
| After any part is disturbed | Reg 26(9) | Test for gas soundness; check the water system is full and free of air; examine water connections hot; carry out functional checks |
The manual says that if the CO/CO2 ratio and CO2 are right and the gas input is at least 90% of nominal, no further action is needed on the burner and heat exchanger that year, subject to the 2-year cleaning limit. Other manufacturers' acceptance figures differ, so take them from the right manual.
Worked example: a school boiler house
A primary school has two wall-hung condensing boilers in a plant room, serving heating only. The school, as employer, has a maintenance contract with a Gas Safe registered firm.
- Booking. The contract has one visit every 12 months, set for July, after the heating season, as the manual suggests.
- Before the visit. The office checks that the engineer booked holds an in-date Gas Safe registration covering commercial boilers, and attaches the service checklist and last year's readings.
- On site. Boiler 1 runs at 94% of nominal gas input, CO/CO2 ratio 0.0015, so it gets its function checks and a flue check. Boiler 2's heat exchanger was last cleaned two summers ago, so it is cleaned this year whatever the readings, to stay within the 2-year limit.
- A defect. A ventilation grille in the plant room door has been covered over. The engineer tells the site manager straight away, records it and the office quotes to fit a proper grille.
- Afterwards. The service section of each boiler's log book is completed, as the manual asks, and the school gets the report the same day.
The readings above are illustrations for the example, not targets: use the figures in your boiler's manual.
Who does what
- The employer or person in control of the premises keeps the appliances, pipework and flues safe (reg 35), uses a Gas Safe registered business, and must not use an appliance they know or suspect is dangerous (reg 34(1)).
- The maintenance contractor is on the Gas Safe Register (reg 3(3)), sends engineers whose registration covers the work, and services to the manufacturer's instructions.
- The engineer carries out the regulation 26(9) checks after the work and tells the responsible person about any defect or danger (regs 26(9) and 34(3)).
HSE says employers can check a person is registered and what they are qualified to do on the Gas Safe Register website or by phoning 0800 408 5500, and that the Gas Safe ID card shows the type of work they are qualified to do.
What to record
GSIUR sets no record format for workplaces. A record that shows each regulation 26(9) check was done, and that the manufacturer's schedule was followed, is the practical evidence the employer needs. For each boiler:
- site, plant room and boiler make, model, serial number and output;
- date, engineer's name and Gas Safe registration number;
- gas rate or operating pressure as measured, against the manual's figure;
- combustion readings: CO, CO2 and the CO/CO2 ratio;
- pass or fail for flue, combustion air and ventilation, gas soundness and safe operation;
- parts cleaned or replaced, and the date the heat exchanger was last cleaned;
- defects, who was told and when, and the action taken;
- the date the next service is due.
Running boiler service contracts in Field Suite
- Your own service checklist: the form library has no commercial boiler form today. Build one with the form builder: number questions with units for gas rate and combustion readings, Pass/Fail/N/A for each regulation 26(9) check, and repeatable groups for each boiler in a plant room.
- Sign-off by a qualified engineer: with the People module on, a form can require an in-date qualification such as Gas Safe, recorded in People and checked by an owner or admin, before the engineer can sign it off. Field Suite checks that the qualification is recorded and in date, not which categories it covers.
- Contracts: a visit every 12 months, created as a job with the form attached a set number of days before it is due.
- Equipment and defects: each boiler sits in the equipment register with its job history. A defect found on site is recorded with its urgency, and the office turns it into a quote.
See planned maintenance software, read about pressure systems in plant rooms and unvented cylinder servicing, check prices, or book a demo.
Field Suite is job management software. The manufacturer's instructions and the Gas Safe registered business decide how a boiler is serviced.
Questions
Is an annual boiler service a legal requirement for a business?
GSIUR does not set a year. It requires the boiler to be kept safe (reg 35). Most manufacturers ask for at least a yearly service, and following the manual is how employers show the boiler is maintained.
Does a commercial boiler need a gas safety certificate?
No certificate of that name is required for a workplace. The annual check and record in regulation 36 apply to appliances serving let homes, including a commercial boiler that also serves flats.
Can a domestic Gas Safe engineer service a commercial boiler?
Only if their registration covers that work. Check the categories on their ID card or on the Gas Safe Register.
Sources
- Gas Safety (Installation and Use) Regulations 1998, regulation 2. https://www.legislation.gov.uk/uksi/1998/2451/regulation/2
- Gas Safety (Installation and Use) Regulations 1998, regulation 3. https://www.legislation.gov.uk/uksi/1998/2451/regulation/3
- Gas Safety (Installation and Use) Regulations 1998, regulation 26. https://www.legislation.gov.uk/uksi/1998/2451/regulation/26
- Gas Safety (Installation and Use) Regulations 1998, regulation 34. https://www.legislation.gov.uk/uksi/1998/2451/regulation/34
- Gas Safety (Installation and Use) Regulations 1998, regulation 35. https://www.legislation.gov.uk/uksi/1998/2451/regulation/35
- Gas Safety (Installation and Use) Regulations (Northern Ireland) 2004. https://www.legislation.gov.uk/nisr/2004/63/contents
- HSE, Gas safety for employers. https://www.hse.gov.uk/gas/employers.htm
- Ideal Heating, Evomax 30 to 150 installation and servicing, UIN 206210 A17 (June 2018), Frames 50, 51 and 52. https://idealcommercialboilers.com/uploads/documents/Evomax-Installation-Guide-206210-17.pdf
Last checked: 5 November 2026 against the sources above.
Checked in detail: GSIUR 1998 regs 2 (definition of work, reg 2(4) excluded premises), 3, 26(9), 34 and 35 on legislation.gov.uk, the NI 2004 Regulations' title page, HSE's gas safety page for employers, and Ideal's Evomax manual UIN 206210 A17 (June 2018) downloaded from idealcommercialboilers.com, Frames 50 to 52 read in full.
Field Suite is job management software for UK building services firms, not a consultancy. Your own risk assessments, contracts and advisers decide what applies to your work. Spotted a mistake? Email info@fieldsuiteapp.com and we correct it.