The idea behind Boiler Plus was simple: when a gas boiler goes in, it should be an efficient one, it should have proper controls, and a combi should come with one extra energy-saving measure. It was introduced by the then Department for Business, Energy & Industrial Strategy and is enforced through Part L (conservation of fuel and power) of the Building Regulations.
Boiler Plus is an England rule. Wales, Scotland and Northern Ireland have their own Building Regulations. Your installer should work to the rules for the country the home is in.
What Boiler Plus requires
- Efficiency: a gas boiler fitted in an existing home must have an ErP seasonal space heating efficiency of at least 92%. Check the boiler’s ErP data sheet, not a headline “up to” figure in a brochure.
- Time and temperature control: the heating must have a timer or programmer and a room thermostat (or one programmable room thermostat that does both). If these are missing or not working, they go in with the boiler.
- One extra measure on a gas combi: when a gas combination boiler is fitted, one of the four measures below must also be installed.
The four options for a gas combi
| Measure | What it does |
|---|---|
| Flue gas heat recovery | A device that pre-heats the incoming cold water for hot water using heat recovered from the boiler’s flue. Some boilers have it built in; others take a separate unit. Check compatibility with the boiler maker. |
| Weather compensation | Measures the outdoor temperature (an outside sensor, or with some controls, local weather data from the internet) and lowers or raises the boiler flow temperature to match. |
| Load compensation | Varies the flow temperature based on how far the room is from the thermostat setting. It usually replaces the room thermostat and needs no extra sensor. |
| Smart thermostat with automation and optimisation | A room thermostat that gives time and temperature control, adjusts its schedule automatically (from your settings or by detecting occupancy), starts the boiler at the right time to reach temperature (optimum start), and can be adjusted remotely. |
Weather and load compensation can work by modulating the boiler, which needs a protocol such as OpenTherm or the maker’s own bus, or by switching the boiler on and off in a way that changes the flow temperature. Modulating control is usually the better choice. A plain on/off “smart” thermostat only counts if it has all of the smart functions listed above.
What changed in 2022
From 15 June 2022 the 2021 edition of Approved Document L, Volume 1 (Dwellings) replaced the old Domestic Building Services Compliance Guide in England. The Boiler Plus rules carried over, and these were added or tightened for gas boiler work:
- A thermostatic control in every room when a boiler is replaced. On a radiator system this normally means TRVs on every radiator except those in the room with the main room thermostat. There are a few narrow exceptions, such as some open-plan single-storey homes.
- Boiler interlock: the controls must switch the boiler and pump off when nothing is calling for heat. TRVs on their own do not do this.
- Sizing: a heat loss calculation, so the boiler is not much bigger than the home needs. What size boiler? explains the basics.
- 55°C flow temperature for full systems: a new or fully replaced wet system (boiler, radiators and pipework) should be designed to run at a maximum flow temperature of 55°C. Where that is not practical, it should be designed for the lowest flow temperature that still heats the home. A boiler-only swap does not have to meet this, but running as cool as the radiators allow still saves gas.
- Commissioning: heating output set to match the heat loss, the system cleaned, flushed and dosed with inhibitor to BS 7593, the radiators balanced, and the Benchmark checklist (or equivalent) completed.
- Handover: the installer must explain the controls and leave instructions on how to use them efficiently.
Oil boilers have their own minimums under the same document: 91% efficiency, or 86% for an oil combi.
Who is responsible
Gas boiler work in the UK must be done by a Gas Safe registered engineer. In England, the engineer notifies the job through Gas Safe’s competent person scheme. You should then get a Building Regulations Compliance Certificate. Keep it, because buyers’ solicitors usually ask for it when you sell.
Both the person doing the work and the property owner are responsible for meeting the Building Regulations. Building control can require non-compliant work to be put right, and it can lead to prosecution. Older articles quote a £5,000 maximum fine. That cap no longer applies, because fines for this offence in England and Wales have been unlimited since 2015. In practice, the simple protection is to use a Gas Safe engineer and check that the controls and extra measure on your quote meet the rules.
Questions to ask on a quote
- What is the boiler’s ErP seasonal efficiency?
- If it is a combi, which of the four Boiler Plus measures is included, and is it a modulating control?
- Will there be TRVs or other room-by-room control in every room except the one with the room thermostat?
- Has a heat loss calculation been done, and what output will the boiler be set to?
- Will the system be flushed and dosed with inhibitor, and the Benchmark checklist filled in?
Related
- Combi boiler installation
- OpenTherm boilers and controls
- Modulating boilers and smart controls
- Vaillant ambiSENSE and weather compensation
- Boiler energy efficiency
- Inhibitor testing
Guidance only, updated from the original hub.myboiler.com Boiler Plus page (2018) and checked against the 2021 edition of Approved Document L, Volume 1, and BEAMA’s Part L heating controls guidance. It covers England. For the exact rules on a job, use the current Approved Document and the boiler and control makers’ instructions.