How to write an O&M manual for a heating installation (UK)

An operation and maintenance manual is the document you leave behind when the heating is finished. Main contractors ask for it at practical completion, managing agents file it, and the homeowner reaches for it the first time the pressure drops or water appears through a ceiling. A good one answers three questions without a phone call to you: what was installed, how do I use it, and how do I turn it off. This guide goes section by section through a manual for a typical domestic job, a system boiler with an unvented cylinder, new radiators and two bathrooms, and shows what to write in each.

Why it is worth doing properly

There are rules behind it. The Gas Safety (Installation and Use) Regulations require the manufacturer’s instructions to be left with the owner or occupier when you install an appliance. The building regulations energy guidance (Approved Document L in England, with equivalents in Wales and Scotland) expects the owner to be given information on operating and maintaining the heating and hot water system. The Benchmark commissioning checklist and boiler warranty both depend on records being handed over and kept. On commercial or managed projects the main contractor may fold your manual into the health and safety file.

The practical reason is simpler. A manual with photos of every valve saves you call-outs for problems the client could have solved, and it is the most professional thing they will hold with your name on it after the job.

The cover and contents page

The cover carries your logo, the words Operation and Maintenance Manual, the property address, the client (often the main contractor or developer rather than the occupier) and the practical completion date. That date matters: warranty periods and the first annual service are counted from it.

Then a contents page with page numbers. It sounds like a detail until the manual is 30 pages long because three certificates and a 20-page boiler manual are in the back. List each numbered section, the contacts table, and each certificate and manual on its own line with the page it starts on.

1. Scope of works

One or two short paragraphs on what you did, in the order a stranger would need it. For example:

“New heating and hot water system installed, comprising a system boiler, unvented hot water cylinder, new controls, radiators and towel rails, with new pipework to all appliances, sanitaryware and the kitchen. A new gas supply has been run inside the flat from the cylinder cupboard to the boiler, with an additional emergency control valve and test point.”

Include anything you altered that someone might later trip over: waste pipework moved, rodding eyes added, extract fans connected to existing ductwork.

2. System description

Where each major component is and what it does. Make, model and location for the boiler, the cylinder, the zone valves, the filter, the filling loop and pressure gauge, the programmer and the room thermostats. Note anything with a backup: an immersion heater on its own fused spur, or dual-fuel towel rails that can run on electric in summer. Take a photo of each component and put it next to the sentence about it.

3. Heating and hot water controls

This is the section the client actually uses. Say where the programmer is, where the room thermostat is (“in the hallway above the light switch”), how to boost the hot water, and where the fused spurs are for the immersion and electric towel rails. If there is a smart thermostat or an app, say which and who set up the account. Keep it to instructions, not features: “press Boost once for one hour of hot water” beats a paragraph on weather compensation.

4. Isolation valves and locations

The section that earns the manual its keep. Every isolation point, where it is, what it looks like and a photo:

Mains water stopcock, and the water meter if there is one inside.
Gas meter and emergency control valve, any additional valve inside the property, and the isolation valve below the boiler.
Cylinder cold inlet and hot outlet isolation valves.
Local valves under basins and sinks, and behind WC flush plates on concealed frames.
Heating isolation valves either side of the boiler and on any manifold.

Describe the handle colour and type (“blue quarter-turn lever”, “red lever on top of the cylinder”). In an emergency nobody reads the second sentence, so put the location first.

5. Bathroom and cloakroom

Extract fans and how they are switched, where the isolation valves for each room are, access panels for concealed cisterns, and any thermostatic mixing valves or shower controls that need occasional attention. If tiles hide something, say so here.

6. Maintenance

Plain intervals and conditions, appliance by appliance:

Boiler: serviced every twelve months by a Gas Safe registered engineer, with the service record in the manufacturer’s book completed, or the warranty may lapse. Inhibitor level checked at each service; magnetic filter cleaned.
Unvented cylinder: checked every twelve months by a competent person (G3 qualified): expansion vessel pre-charge, pressure reducing valve, temperature and pressure relief valve, and the tundish and discharge pipe.
Extract fans: grilles cleaned periodically; filters if fitted.

Give the warranty length and the date it runs from, and say plainly what voids it.

Useful contact numbers

A short table: your office and out-of-hours number, the boiler and cylinder manufacturers’ service lines, the gas emergency number (0800 111 999 in Great Britain), the water supplier and the electricity network operator’s power cut number (105). Check each one is current on the day you hand over.

Certificates and manuals

The back of the manual holds the paperwork, in a fixed order:

Gas safety record or commissioning certificate for the work.
Benchmark commissioning checklist for the boiler, and for the cylinder if supplied.
Unvented hot water (G3) installation certificate.
Building regulations compliance certificate, or a note that it will follow by post.
Warranty registration confirmations.
Manufacturers’ installation and user manuals.

Most of these exist as PDFs from the certificate app you already use; a few, often the Benchmark, are still on paper. Photograph paper certificates flat, in good light, square to the page, so they read cleanly when printed.

Handing it over

Send it on the day of practical completion, as a single PDF rather than a folder of attachments, so it can be forwarded to the occupier, the managing agent and the next engineer without anything getting lost. If the main contractor wants paper, print the same file. Keep your own copy; the next call-out will be quicker with it open.

Writing it without the evening in Word

The slow part of an O&M manual is not knowing what to write; it is the assembly: photos pasted into the right section, the contents page renumbered every time a certificate is added, PDFs merged at the end. Two ways round it:

Start from our free O&M manual template (Word and PDF, no sign-up), which has every section above with prompts.
Or write it on your phone with Docutrades O&M manual software: short notes and photos per section, certificates uploaded as PDFs or photos, and one tap produces the branded PDF with the contents page numbered and the certificates merged in.

A checklist before you hand over

Cover: property, client, practical completion date, your details.
Contents page numbers match the final file.
A photo of every isolation valve, with its location first.
Controls explained as instructions, not specifications.
Service intervals, warranty length and start date stated.
Contacts checked on the day.
Every certificate legible, in order, and signed.
One PDF, sent the same day.

Written and edited by the Docutrades team, from real handover manuals produced for domestic plumbing and heating refits. Published 21 October 2026. This guide is general information, not legal advice; check the regulations and manufacturers’ requirements that apply to your installation.