Boiler Plus explained:the controls every new boiler needs

What is Boiler Plus?

Boiler Plus was a government policy that raised the minimum standard for replacement boilers. The then Department for Business, Energy and Industrial Strategy published it as an amendment to the Domestic Building Services Compliance Guide, the guidance that sat under Approved Document L of the Building Regulations. From April 2018 it applied whenever a boiler is installed in an existing heating system anywhere in England, whether replacing an old one or fitting one for the first time in an existing home.

It does not force anyone to replace a working boiler. The government's factsheet is explicit that there is no requirement to retrofit: the standards only bite when a boiler is installed.

What must every new gas boiler have?

The Boiler Plus requirements now sit in Approved Document L, Volume 1: Dwellings (2021 edition incorporating 2023 amendments), the edition in force for work in existing homes today. When a boiler is replaced, it sets out:

TRVs should not be fitted in the same room as the thermostat, because the two would fight each other. If radiators need new valves when the boiler is replaced, a TRV fitted on the same visit is a £42 add-on in our prices.

What are the four extra measures for a combi?

• Flue gas heat recovery. A unit on or in the boiler that captures heat from the hot flue gases and uses it to preheat the incoming cold water.
• Weather compensation. An outdoor sensor tells the boiler how cold it is outside, and the boiler varies its flow temperature to match, as Approved Document L defines it.
• Load compensation. A control that maintains the room temperature by varying the boiler's flow temperature against how the heating system is responding, again in Approved Document L's definition.
• Smart thermostat with automation and optimisation. Automation means it adjusts time and temperature settings automatically from occupancy detection or from what it has learned of your adjustments over time. Optimisation, in general terms, means it works out when to start heating so the home reaches temperature at the time you set.

System and regular boilers do not need the extra measure. The factsheet explains that many of them would need extra work to use these devices safely, and warns that without the right knowledge there may be a risk of Legionella, so the rule was applied to combis first.

Why is a basic thermostat not enough?

A programmable thermostat meets the time and temperature requirement, but on its own it is not one of the four combi measures. Two points in the government's Boiler Plus FAQs catch people out:

• TPI does not count. Time proportional and integral controls switch the boiler on and off in timed bursts. The FAQs state that the load compensation description should not be read as including TPI controls, and that TPI is not in scope.
• Being 'smart' is not enough. Boiler Plus requires specific functions with proven benefits: load compensation, weather compensation, or automation combined with optimisation. The FAQs note that more basic smart controls may help, but that their benefit remains unproven.

Do weather and load compensation actually save anything?

They can, and the reason is condensing. A condensing boiler recovers heat from its flue gases, and it only does that well when the water coming back to it is cool enough. Worcester Bosch's installer guidance says a condensing boiler kept below 50°C can run up to 10% more efficiently than at higher temperatures. Compensation controls keep the flow temperature as low as the weather or the room allows, instead of running hot and switching off.

The honest caveats, several of them from Glow-worm's own guidance:

• Radiators may not feel as hot as before. The room reaches the same temperature more gently and holds it more evenly.
• It works best in a reasonably insulated home with radiators large enough to heat rooms at lower temperatures. Worcester Bosch advises checking heat loss and radiator sizes before relying on low flow temperatures.
• The outdoor sensor needs a sensible position, and Glow-worm recommends a north-facing wall, out of direct sun.
• Savings depend on your home and habits. Nobody can promise a fixed percentage off your bill in advance.

If you are weighing a new boiler against a heat pump, see heat pump costs.

How do you know a new boiler meets Boiler Plus?

• Ask which of the four measures a combi quote includes, by name. If the answer is 'a programmable thermostat', it is not compliant.
• Ask for the completed Benchmark Commissioning Checklist. Approved Document L names it as a way to show commissioning was carried out satisfactorily, and the Benchmark scheme says the engineer is legally required to complete a commissioning checklist to comply with Building Regulations. Check it lists the controls fitted.
• Keep the Building Regulations paperwork your installer gives you after notifying the work. You will need it when you sell.

Every Smart Energie boiler price includes this line: A Boiler Plus compliant smart control, with automation and optimisation, or weather compensation where the boiler supports it. If you already own a compatible smart control, reconnecting it costs nothing. See the full list of inclusions in how much a new boiler costs, or get your fixed price.

Common questions