Bringing heating plant back after summer: a pre-season recommissioning guide

Commercial engineers covering Suffolk, Essex and Cambridgeshire

Winter gas safety: smell gas? Call National Gas Emergency on 0800 111 999. For commercial boiler breakdowns call 0800 0996 007.

Pre-season recommissioning means bringing heating plant back into service after the summer in a planned, checked order instead of just switching it on and waiting for complaints. For a commercial building that usually means: book the annual service or a start-up visit with a Gas Safe registered commercial engineer before the cold weather, have the engineer check the boilers, burners, flues, ventilation, pressurisation equipment and pumps that have sat idle, reset time clocks and holiday programmes for winter occupancy, and make sure the hot water side is still being run at the temperatures your legionella risk assessment requires. Site staff have a clear but limited role: look, log readings and report anything abnormal. This guide sets out what an engineer typically checks at start-up, what your team can do before and after, and the records worth keeping. If your plant is already running this winter, use it as a check that nothing was missed, and as a plan for next autumn.

A team of over 10 local engineers to call on · Gas Safe 985448 · Call 0800 0996 007 · WhatsApp 07947 578332

Commercial heating tips and advice · 13 November 2026 · Fast Commercial Boiler Help, Gas Safe 985448

Why heating plant needs recommissioning after summer

Through the summer, space heating plant in most commercial buildings is either switched off or running only to keep hot water going. Months of standing still causes its own problems:

Pumps and valves that have not moved. Hamworthy's servicing schedule for its Weymouth pressurisation units, for example, includes a six-monthly task to "Briefly run the pump to check for rotor seizure. This could occur if the pump is not run for extended periods." The same logic applies to circulating pumps and motorised valves that have been idle since spring.
Controls set for summer. Time clocks, holiday programmes and BMS schedules are often changed for the quiet months, and settings can be lost after a power cut.
Plant rooms used as storage. Summer is when boxes, furniture and cleaning stock tend to end up in plant rooms, in front of ventilation grilles or next to boilers.
Faults left from last winter. A boiler that locked out in March and was only reset may still have the same fault when it is asked to work hard again.
Hot water that has been little used. In buildings that were quiet over the summer, such as schools, offices with reduced occupancy and seasonal venues, hot water outlets and parts of the system may have stood with little flow.

None of this is unusual. The aim is to find it on a planned visit, in daylight and mild weather, instead of on the first cold Monday morning.

Heating plant pre-season recommissioning: who does what

The work splits clearly between the competent engineer and site staff.

Gas work is for Gas Safe registered engineers only. Regulation 35 of the Gas Safety (Installation and Use) Regulations 1998 places a duty on every employer or self-employed person to ensure that any gas appliance, installation pipework or flue installed at any place of work under their control "is maintained in a safe condition so as to prevent risk of injury to any person." HSE's guidance for employers says to use a Gas Safe registered engineer or competent person to install, maintain or repair gas fittings, and "Do not use any appliance you know or suspect is unsafe." Manufacturers say the same. Ideal's Evomax 2 commercial boiler user guide states that the boiler "must be installed and maintained by a suitably qualified Gas Safe registered engineer" and "should be serviced at least once a year" by one. It also says that if a fault is known or suspected, the boiler "MUST NOT BE USED until the fault has been corrected by a suitably qualified Gas Safe registered engineer".

Site staff look, log and report. Trained site staff can carry out visual and gauge checks, keep plant rooms clear, record readings and fault codes, and report anything abnormal. They should not remove boiler casings, adjust burners or gas valves, work on flues, override safety controls, or adjust, cap or test-lift pressure relief valves.

CIBSE Guide M (Maintenance engineering and management) covers commissioning and testing as one of its parts (Part M6), and BESA's SFG20 standard maintenance schedules include a "Mothballing & Reactivation" set of schedules alongside the core library. If you work to a planned maintenance contract, ask your contractor which SFG20 tasks or manufacturer tasks they will carry out at the autumn visit.

What the engineer checks at start-up

The exact tasks depend on the plant and the manufacturer's instructions, but a pre-season visit by a competent engineer typically covers:

The annual service, if due. Timing the boiler service for late summer or early autumn means the plant goes into winter freshly serviced. Our guide to what a commercial boiler service includes walks through the usual steps, including combustion checks, flue and safety control checks.
Gas supply, burners and safety controls. Lighting each boiler or module, checking ignition, flame supervision and lockout behaviour, and confirming that any interlocks (for example ventilation or fan interlocks) work as designed.
Flues and ventilation. Checking flue routes and terminals for damage or obstruction after the summer, and that plant room ventilation openings are clear. The Evomax 2 user guide tells users "Do not obstruct ventilation ducts, condensate pipework, grilles or openings in the boiler room". See our guide to plant room ventilation for gas boilers.
System pressure and pressurisation equipment. Checking the system is at the pressure set at commissioning, and that the pressurisation unit and expansion vessels are working. Hamworthy's Weymouth schedule, for example, lists checking the expansion vessel charge pressure every six months. Our guides to reading a commercial heating pressure gauge and expansion vessels and pressurisation units explain what site teams should watch for.
Pumps and valves. Confirming circulating pumps start and run without noise or overheating, duty and standby pumps change over, and motorised valves and actuators move.
Air and circulation. Venting air that has collected, and checking each zone heats up when called.
Water treatment. Ask whether your maintenance regime includes sampling the closed heating system water. Our guide to water treatment for commercial heating systems explains why it matters.
Controls handover. Leaving the boilers under the correct automatic control, with fault codes cleared only once the cause has been found, and telling you about anything that needs a follow-up visit.

If anything fails a check, the engineer should explain the risk and record it. HSE's advice is clear: do not use any appliance you know or suspect is unsafe, so do not ask anyone to "just get it running" past a safety fault.

Pressure systems and the written scheme of examination

Most low temperature hot water heating systems in commercial buildings are maintained to the manufacturer's instructions by a competent engineer. Some plant is covered by the Pressure Systems Safety Regulations 2000 (PSSR). HSE's INDG178 explains that a written scheme of examination covers items that operate under pressure and contain a "relevant fluid", which includes "pressurised hot water above 110 °C" and compressed gases above 0.5 bar. Where PSSR applies, HSE's INDG261 says the written scheme "must cover all protective devices", that the system "must be examined in accordance with the written scheme by a competent person", and that after a major repair or modification "you may need to have the whole system re-examined before allowing the system to come back into use."

So if part of your plant is under a written scheme, check before restart that the examinations due under the scheme are up to date and that any work done over the summer has been considered by your competent person. HSE's L122 Approved Code of Practice gives the detail. Where PSSR does not apply, relief valves, expansion vessels and pressurisation units should still be maintained to the manufacturer's instructions by a competent engineer. Either way, site staff should only look at gauges, record readings and report anything outside the range the engineer set. Never adjust, cap or test-lift a relief valve.

Controls, time clocks and holiday programmes

Controls are worth checking first at the start of the season, because they are the part site teams can usually check themselves through the normal user interface:

Time clocks. Commercial boiler controllers often have several heating periods per day. The Evomax 2, for example, lets each heating circuit be "programmed to a specific time clock with three periods per day" and have "up to 8 holiday periods". Check that summer settings and holiday dates have been replaced by your winter occupancy times.
The clock change. GOV.UK confirms that UK clocks go back "1 hour at 2am on the last Sunday in October". Check that controllers, time switches and BMS outstations show the correct time afterwards, especially older units that do not change automatically.
Setpoints and frost protection. Confirm that room and flow temperature setpoints are as your engineer left them, and that frost protection settings are enabled for the winter. Our guide to frost protection for commercial heating plant covers this in detail.
BMS alarms. If you have a building management system, check that alarms are reaching someone who will act on them. See our BMS and heating controls tips.

Changing schedules through the user menu is normal. Changing commissioning or engineer-level settings is a job for your engineer, and those menus are usually protected for that reason.

Hot water and legionella after a quiet summer

Restarting space heating often coincides with buildings filling up again, which makes it a good point to check the hot water side. HSE's Approved Code of Practice L8 and its technical guidance HSG274 Part 2 apply to hot and cold water systems in workplaces. HSE says: "Hot water should be stored at least at 60°C and distributed so that it reaches a temperature of 50°C (55°C in healthcare premises) within 1 minute at the outlets."

Points HSG274 Part 2 makes that are relevant at start-up:

Little-used outlets. "When outlets are not in regular use, weekly flushing of these devices for several minutes can significantly reduce the risk of legionella proliferation in the system. Once started, this procedure has to be sustained and logged, as lapses can result in a critical increase in legionella at the outlet."
Standby plant. "Standby pumps should be used at least once each week to avoid water stagnation, and standby calorifiers need a suitable procedure to ensure the risk is controlled before they are brought back into service."
Buildings taken out of use. Where a building, part of a building or a water system has been taken out of use (sometimes called mothballing), HSG274 says it "should be managed so that microbial growth, including legionella in the water, is appropriately controlled", and that such systems "should be recommissioned as though they were new (ie thoroughly flushed, cleaned and disinfected) before returned to use."
Monthly temperature checks. HSG274's checklist includes monthly checks of calorifier flow temperatures (as close to 60°C as practicable without going below 60°C) and return temperatures (not below 50°C).

Your legionella risk assessment and written control scheme decide what applies on your site, and the person appointed to manage the risk should agree any start-up flushing or temperature checks. HSE's records guidance says records should include "details of the state of operation of the system (in use/not in use)" and that monitoring records "should be retained for at least 5 years". Our guide to legionella and hot water temperatures in commercial buildings explains how heating plant affects those temperatures. Gas-fired water heaters and calorifier heat sources need the same Gas Safe registered engineer as the boilers.

A pre-season recommissioning checklist

Check	Who	When
Autumn service or start-up visit booked for boilers, water heaters and space heaters	Facilities manager	Late summer, before the heating is needed
Plant room cleared of stored items; ventilation grilles and access to plant unobstructed	Site staff	Before the engineer's visit
Last winter's faults, lockouts and repairs listed for the engineer	Facilities manager	Before the visit
Boilers, burners, flues, safety controls and interlocks checked and serviced	Gas Safe registered commercial engineer	At the visit, and at least annually
System pressure, pressurisation unit and expansion vessels checked; pumps and valves run	Competent engineer	At the visit, to manufacturer intervals
Written scheme examinations up to date where PSSR applies	Duty holder and competent person	Before restart
Time clocks, holiday programmes and setpoints set for winter; correct time after the clocks go back	Facilities manager or site staff (user menus only)	Before restart and after the last Sunday in October
Hot water temperatures and flushing of little-used outlets in line with the legionella control scheme	Person managing legionella risk	As the scheme requires (often weekly and monthly)
Gauge readings logged against the engineer-set range; lockouts reported, not reset again and again	Trained site staff	Weekly, and as faults happen
Service reports, gas safety records and any examination reports filed	Facilities manager	After the visit

Logging the first weeks of the season

The first few weeks after restart are when idle-season problems show up. A simple log makes them much easier to diagnose: date and time, outside conditions, system pressure reading, boiler status or fault code, which zones were cold, and what was done. If a boiler locks out, write down the code before anything else. The Evomax 2 user guide says that "In cases of repeated or continuous shutdown a suitably qualified Gas Safe registered engineer ... should be called to investigate and rectify the condition causing this". Our boiler lockout log sheet shows what to record.

If you suspect a gas leak at any point, HSE's advice for employers is to turn off the supply and immediately phone the National Gas Emergency Service on 0800 111 999 (or your LPG supplier, for LPG), and if in doubt, evacuate the building.

Need your heating plant brought back into service?

Our Gas Safe registered engineers (985448) service and recommission commercial boilers, water heaters and plant rooms. See our commercial boiler servicing page or our planned preventive maintenance contracts to get the autumn visit on a schedule. For faults found at start-up, see plant room repair, commercial boiler repair or our emergency commercial boiler repair page. Call 0800 0996 007, WhatsApp 07947 578332 or email [email protected]. Photos of the boiler rating plates and any fault codes help us prepare.

Safety note

Under the Gas Safety (Installation and Use) Regulations 1998, gas work must be carried out by a Gas Safe registered engineer, and we apply that rule on every site. Don't attempt DIY work on gas appliances, burners, flues or safety devices. On pressure systems, trained site staff should stick to visual and gauge checks, log the readings and report anything abnormal. Never adjust, cap, plug or test-lift a relief valve yourself.

Talk to a Gas Safe commercial engineer

Fast Commercial Boiler Help is a Gas Safe registered (985448) commercial heating business based at 4 Market Hill, Clare, Sudbury, Suffolk CO10 8NN. Our team of over 10 local engineers covers East Anglia and East London, working on commercial boilers, plant rooms, water heaters, and warm air, radiant and unit heaters. We work on commercial premises only.

Call 0800 0996 007

Call or WhatsApp 07947 578332 (a photo of the appliance data plate or the fault display helps) · Email [email protected]

Frequently asked questions

What is pre-season recommissioning of heating plant?

It is the planned process of bringing commercial heating plant back into service after the summer: an engineer's start-up or service visit, checks on boilers, flues, ventilation, pressurisation equipment, pumps and controls, resetting time clocks for winter, and confirming hot water is still controlled in line with the legionella risk assessment.

When should we book the autumn start-up visit?

Before the heating is needed, so faults are found in mild weather rather than on the first cold day. It can be combined with the annual boiler service. Manufacturers such as Ideal state that their commercial boilers should be serviced at least once a year by a Gas Safe registered engineer.

Can our caretaker or site staff restart the boilers?

Site staff can use the normal user controls, such as time clocks and on/off switches, as set out in the manufacturer's user instructions, and carry out visual and gauge checks. Work on gas appliances, burners, flues and safety devices must be done by a Gas Safe registered engineer. If a fault is known or suspected, the boiler should not be used until it has been put right.

Does legionella control matter when we restart the heating?

Yes, where heating plant also heats water or the building has been quiet. HSE says hot water should be stored at least at 60°C and reach 50°C (55°C in healthcare premises) within 1 minute at outlets. HSG274 says little-used outlets should be flushed weekly, and systems taken out of use should be recommissioned as though they were new before use. Follow your own risk assessment and control scheme.

Does PSSR apply to our heating system?

It depends on the plant. HSE says a written scheme of examination covers systems containing a relevant fluid, which includes pressurised hot water above 110°C. Where PSSR applies, examinations must be carried out by a competent person in line with the written scheme. Where it does not, pressure safety devices should be maintained to the manufacturer's instructions by a competent engineer.

What should we record after restarting the heating?

Keep the engineer's service and check reports, gas safety records and any written scheme examination reports, plus a simple log for the first weeks: pressure readings, fault codes, cold zones and what was done. HSE says legionella monitoring records should be kept for at least 5 years.

Sources and further reading