New gas boiler: what the regulations add to the job

In England, Approved Document L sets a minimum efficiency for gas boilers in existing homes, which in practice means a modern condensing boiler. When a gas combi boiler is installed, at least one extra energy efficiency measure is expected: flue gas heat recovery, weather compensation, load compensation, or a smart thermostat with automation and optimisation. The installer should say which one they are fitting and why.

When a boiler is replaced, each heated room should also get thermostatic control, usually a room thermostat in one room and thermostatic radiator valves on the radiators elsewhere, but not in the room with the thermostat. Heating and hot water need separate time control where the system has a stored cylinder. If your quote has no line for controls or valves, ask why.

Since a boiler replacement is notifiable work, a Gas Safe registered installer notifies Building Control through the scheme and you receive a compliance certificate, normally within eight weeks. The Benchmark commissioning checklist completed on the day is your record that the boiler was set up to the manufacturer's instructions.

Source: gov.uk

The flue position has to meet the manufacturer's clearances from windows, doors, boundaries and other openings, which is why a new boiler cannot always go where the old one was, particularly when an older non-condensing model had a flue in a spot that no longer complies. A condensing boiler also produces acidic condensate that must drain away safely; external condensate pipes are a common cause of winter breakdowns when they freeze, so the route and insulation matter.

Under the Building Regulations in England, installing a fixed combustion appliance in a home brings a requirement to provide a carbon monoxide alarm. Ask where it will go if your quote does not mention one.

Like-for-like replacements in the same position cost least. Moving the boiler, changing type, a larger gas supply pipe from the meter, a new flue route through a roof, a system flush on old sludgy pipework, and the controls required by the regulations all add to the bill. A new gas boiler is standard-rated for VAT; the zero rate for energy-saving materials does not cover it.

Ask whether the price includes a power flush or chemical clean and a magnetic filter, what the manufacturer's warranty length depends on, and whether it needs registering. Warranties often require annual servicing by a Gas Safe engineer.

• boiler make, model and output, and the reason for that size
• the extra efficiency measure for a combi, and the thermostat and valves
• flue route and any changes to the gas pipe
• system clean, inhibitor and filter
• removal of the old boiler, cylinder or loft tanks if the type changes
• carbon monoxide alarm, Benchmark checklist and Building Control notification

Existing homes can still have a new gas boiler; the Future Homes and Buildings Standards being introduced in England concern new homes. If you are replacing a boiler anyway, it can be worth asking whether a heat pump would suit the house, because the Boiler Upgrade Scheme only funds low-carbon heating. If a heat pump is not for you now, specify radiators and pipework that could work at lower temperatures later.

Tell us the current boiler, where it is and what you want. After your phone and email are confirmed, Gas Safe engineers in your area see the job without your personal details, and exactly one can buy it. The engineer pays Offrano; the request is free for you.

You receive the engineer's business name, address and phone number by email before your details are released. Nobody is obliged to take the job, and you remain free to get other quotes. We check the buyer is a registered business, not whether it is on the Gas Safe Register, so look up the registration and the categories on the engineer's ID card yourself.