Heating Controls and Boiler Plus: What's Required by Law?

Summary

Boiler Plus is an amendment to the Domestic Building Services Compliance Guide that came into force on 6 April 2018 in England, introduced by the Department for Business, Energy and Industrial Strategy (BEIS, now DESNZ). It sets minimum standards for domestic gas boiler replacements to reduce carbon emissions and improve heating efficiency. The legislation requires all replacement boilers to meet 92% ErP efficiency and have time and temperature zone controls fitted. Combi boilers carry an additional requirement: one of four specified energy-saving measures must be installed alongside the boiler. Installers must notify Building Control (either directly or via a Competent Persons Scheme such as Gas Safe) and complete the Benchmark Commissioning Checklist to demonstrate compliance.

Key Facts

• Boiler Plus applies to England only -- Scotland and Wales have separate but similar requirements introduced later (2022)
• All replacement gas boilers must achieve a minimum 92% ErP seasonal efficiency
• All replacement boilers (combi, system, and regular) must have time and temperature controls fitted
• Combi boiler replacements must include one additional measure from a list of four options
• System and regular (heat-only) boiler replacements in England do not require an additional measure beyond time and temperature controls
• The additional measure requirement is flexible -- the installer chooses the most suitable option for the property and household
• Building Regulations notification is mandatory, either directly to LABC or via a Competent Persons Scheme (e.g., Gas Safe Register)
• The Benchmark Commissioning Checklist must be completed and handed to the customer as evidence of compliance
• Non-compliance is a Building Regulations Part L offence -- building control can require remedial work

Boiler Plus Requirements Summary

Detailed Guidance

What does Boiler Plus require when I replace a boiler?

There are two tiers of requirement under Boiler Plus:

Tier 1 -- All boiler types (combi, system, regular):

• The replacement boiler must have a minimum seasonal efficiency of 92% ErP. In practice, every current-production condensing boiler from major UK manufacturers (Worcester, Vaillant, Ideal, Baxi, Viessmann) meets or exceeds this threshold.
• Time and temperature controls must be fitted. This means a room thermostat (or programmable room thermostat) plus a timer or programmer. A basic room stat with a separate time clock satisfies this requirement, though most installers now fit a combined programmable thermostat as standard.

Tier 2 -- Combi boilers only (additional measure):

• When replacing a gas combination boiler, one additional energy efficiency measure must be installed from the following four options: (1) a smart thermostat with automation and optimisation functions, (2) load compensation, (3) weather compensation, or (4) flue gas heat recovery.
• Only one measure is required, not all four. The installer selects the most appropriate option for the property.
• The measure must be installed at the time of the boiler replacement -- retrofitting later does not satisfy the requirement for the original installation notification.

What are the four additional measures for combi boilers?

1. Smart thermostat with automation and optimisation

BEIS defines a compliant smart thermostat as a control that combines the functions of a room thermostat and central timer, plus both of the following:

• Automation: The device automatically adjusts time and temperature settings based on occupancy detection, geolocation, or learned patterns from user behaviour over time. A basic remote-controlled thermostat without learning or occupancy features does not qualify.
• Optimisation: The device calculates how long the property takes to reach the desired temperature and starts the heating system at the optimal time to reach setpoint by the programmed start time, minimising energy use.

A thermostat that only offers remote smartphone control without automation and optimisation does not satisfy Boiler Plus. The thermostat must have both features.

2. Load compensation

Load compensation measures the difference between the current room temperature and the thermostat setpoint, then modulates the boiler's flow temperature accordingly. When the room is far from setpoint, the boiler fires at a higher flow temperature; as the room approaches setpoint, the flow temperature is reduced. This keeps the boiler in condensing mode for longer and reduces fuel consumption.

Load compensation can be delivered through:

• OpenTherm-compatible controls communicating directly with the boiler's PCB to modulate flow temperature
• TPI (Time Proportional & Integral) controls that cycle the boiler on/off in calculated intervals based on the temperature gap, rather than simple on/off switching
• Built-in boiler controls -- many modern boilers have load compensation integrated into their PCBs when paired with the manufacturer's own controls

3. Weather compensation

Weather compensation uses an external temperature sensor (mounted on a north-facing wall) to adjust the boiler's flow temperature based on outdoor conditions. When it is milder outside, the boiler reduces its flow temperature; when it is colder, it increases it. This is the most efficient control strategy for condensing boilers because it continuously optimises the flow temperature for the actual heating demand.

Weather compensation requires:

• An outdoor sensor (supplied as a kit by the boiler manufacturer or as a third-party accessory)
• A boiler with a weather compensation input or OpenTherm capability
• Correct commissioning of the heating curve to match the property's heat loss characteristics

4. Flue gas heat recovery (FGHR)

FGHR systems recover waste heat from the boiler's flue gases and use it to preheat incoming cold water before it enters the boiler. This reduces the energy needed to heat domestic hot water. FGHR units are typically built into or mounted on the boiler and are specified at the point of purchase.

FGHR is most effective in properties with high DHW demand. It is less commonly specified than the other three options because it adds significant cost to the boiler and the efficiency gains are modest for average households.

Which smart thermostats satisfy Boiler Plus?

To comply with Boiler Plus, a smart thermostat must provide automation and optimisation -- not just remote control. The following table compares the main options available to UK installers. All listed models satisfy Boiler Plus when correctly installed.

Installer guidance on choosing:

• Fitting a Worcester boiler? Specify the Worcester Wave -- it gives you load/weather compensation plus smart control in one package, simplifying compliance.
• Fitting a Vaillant boiler? Specify the vSMART for the same reason -- integrated load compensation and smart features.
• Fitting any other brand (Ideal, Baxi, Viessmann, etc.)? Nest or tado are the strongest universal choices. If the boiler supports OpenTherm, pair it with a Nest or tado for modulating load compensation as a bonus.
• Customer wants multi-zone? Evohome or tado with smart TRVs. Wiser is a cost-effective alternative.
• Customer on a budget? Hive at GBP 150 is the lowest-cost compliant option, though it lacks OpenTherm modulation.

What about load compensation and weather compensation?

These are the two non-smart-thermostat control strategies that satisfy Boiler Plus for combis. They are worth considering when a customer does not want a smart thermostat or when the property would benefit more from boiler modulation than from smartphone control.

Load compensation is the simpler of the two. It is delivered through:

• OpenTherm controls: Third-party thermostats (Nest, tado, Honeywell T6R) communicating with an OpenTherm-compatible boiler. The thermostat tells the boiler what flow temperature is needed based on the room temperature gap.
• Manufacturer controls: Worcester Wave, Vaillant vSMART, Ideal Halo, Baxi uSense -- these provide load compensation through proprietary protocols.
• TPI thermostats: Budget options like the Salus RT520 provide load compensation through intelligent on/off cycling. These satisfy Boiler Plus without requiring OpenTherm or a smart thermostat.
• Built-in: Some boilers (particularly Vaillant ecoTEC and Viessmann Vitodens ranges) have load compensation logic built into the PCB that activates with any compatible room thermostat.

Weather compensation requires an outdoor temperature sensor and is the most energy-efficient control strategy because it continuously adjusts flow temperature based on actual external conditions. It is particularly effective for:

• Well-insulated properties where low flow temperatures (40-50 degrees C) are sufficient for most of the year
• Underfloor heating systems that operate at low flow temperatures by design
• Properties with large radiator surfaces (oversized radiators)

Boiler manufacturers that offer weather compensation sensor kits:

• Worcester Bosch: Outside weather sensor for Greenstar range (connects to boiler PCB directly)
• Vaillant: VR21 outdoor sensor for ecoTEC range
• Ideal: Ideal outdoor sensor for Logic/Vogue range
• Viessmann: Vitotrol outdoor sensor for Vitodens range
• Baxi: Outdoor sensor kit for Platinum/800 range

Weather compensation is often a better compliance route than a smart thermostat for properties where the occupants are elderly, non-technical, or unlikely to use an app. It is a "fit and forget" solution that delivers genuine efficiency gains without requiring user interaction.

Does Boiler Plus apply in Scotland, Wales, and Northern Ireland?

England: Boiler Plus has been in force since 6 April 2018. It applies to all domestic gas boiler replacements.

Wales: Wales adopted equivalent requirements through updates to Part L of the Welsh Building Regulations, effective from 23 November 2022. The requirements are broadly the same as England -- combi replacements need an additional measure.

Scotland: Scotland introduced Boiler Plus-equivalent requirements in December 2022 through the Domestic Building Services Compliance Guide. Crucially, Scotland goes further than England: the additional energy efficiency measure requirement applies to all boiler types (combi, system, and regular), not just combis. This is a significant difference for installers working in Scotland.

Northern Ireland: As of early 2026, Northern Ireland has not formally adopted Boiler Plus. Building Regulations Part F (Conservation of fuel and power) applies, requiring minimum boiler efficiencies and basic time and temperature controls, but there is no equivalent additional measure requirement for combi installations. Installers should check the current Building Control guidance as this may change.

Frequently Asked Questions

Can I fit a basic programmable thermostat and claim Boiler Plus compliance for a combi?

No. A standard programmable room thermostat (e.g., Honeywell T3, Drayton Digistat) satisfies the time and temperature control requirement but does not satisfy the additional measure requirement. You must also install one of the four additional measures. However, if the boiler has built-in load compensation that activates with any room thermostat (check the manufacturer's documentation), then a basic programmable thermostat plus the boiler's built-in load compensation together satisfy both requirements.

Does the customer have to actually use the smart thermostat app for it to be compliant?

No. Compliance is determined at the point of installation, not ongoing usage. The thermostat must be capable of automation and optimisation and must be installed and commissioned correctly. Whether the customer chooses to use the app or enable all features is their decision.

What if the customer refuses a smart thermostat -- can I still comply?

Yes. Specify load compensation, weather compensation, or FGHR instead. Weather compensation with an outdoor sensor is an excellent alternative that requires no customer interaction with technology. If the boiler supports OpenTherm, a standard programmable thermostat connected via OpenTherm provides load compensation and satisfies the additional measure without being a "smart" thermostat.

Who enforces Boiler Plus?

Building Control enforces it, either the Local Authority Building Control (LABC) or an Approved Inspector. If the installation is notified through the Gas Safe Register's Competent Persons Scheme, the notification itself serves as the Building Regulations compliance mechanism. If the additional measure is missing, Building Control can require remedial work. The Benchmark Commissioning Checklist provides documented evidence of compliance.

Does Boiler Plus apply to oil boilers?

No. Boiler Plus specifically covers gas-fired boilers. Oil boiler installations are governed by Building Regulations Part L and the Domestic Building Services Compliance Guide, which require time and temperature controls and minimum efficiency standards, but do not mandate the four additional measures.

Does Boiler Plus apply to new builds?

Boiler Plus covers replacement boiler installations in existing dwellings. New builds are covered by the full Building Regulations Part L (Conservation of fuel and power), which has its own set of requirements typically enforced through SAP calculations and is generally more stringent than Boiler Plus.

Regulations & Standards

• Boiler Plus -- Heat in Buildings: Boiler Plus (BEIS, April 2018) -- amendments to the Domestic Building Services Compliance Guide for England

• Building Regulations Part L -- Conservation of fuel and power (England and Wales)

• BS EN 12828 -- Heating systems in buildings: design for water-based heating systems

• Benchmark Scheme -- HHIC (Heating and Hotwater Industry Council) commissioning and installation standards

• Gas Safety (Installation and Use) Regulations 1998 -- legal requirement for Gas Safe registered engineers

• Domestic Building Services Compliance Guide -- the technical companion document to Part L, which Boiler Plus amends

• BEIS Boiler Plus Factsheet (GOV.UK)

• HHIC Boiler Plus Installer Guidance

• BEIS Guidance on Boiler Plus Compliance (via Intergas)

• BRE Evidence Gathering -- Compensation and TPI Controls (GOV.UK)

• BEAMA -- Defining Smart Controls

• Gas Safe Register -- Boiler Plus Guidance

• Worcester Bosch -- Boiler Plus Legislation

• Vaillant -- How To Comply with Boiler Plus

• Ideal Heating -- Boiler Plus Guide

• Ideal Heating -- Part L Changes in Wales and Scotland

• The Heating Hub -- Focus on Boiler Plus

• The Heating Hub -- OpenTherm Compatibility Guide

• boiler selection -- Boiler sizing guide

• hot water systems -- Boiler type comparison

• building control -- Building control requirements