Since 2018, a replacement gas boiler in England must meet a minimum efficiency and be fitted with time and temperature control. Combis must also have one of four additional measures, and they are not equally effective.
What it requires
Boiler Plus came into effect in England in April 2018 and applies to gas boiler installations in existing dwellings. Its requirements are:
- A minimum seasonal efficiency for the appliance.
- Time and temperature control – a programmer and a room thermostat, or a combined device. This effectively ends the practice of fitting a boiler with no room thermostat.
- For combi boilers specifically, one additional energy efficiency measure from a defined list of four.
It applies to England. Requirements elsewhere in the UK differ, and standards have continued to develop since, so any current installation should be discussed against what applies now rather than against a remembered rule.
The four combi options, ranked by what they actually do
| Measure | What it does | Our view |
|---|---|---|
| Weather compensation | An outdoor sensor lets the boiler vary its flow temperature with the weather | The best of the four. Keeps the boiler condensing far more of the time, and improves comfort |
| Load compensation | The boiler modulates down as the room approaches temperature, rather than running flat out then stopping | Close behind weather compensation, and easier to retrofit |
| Flue gas heat recovery | A device recovers heat from the flue to preheat incoming cold water | Genuinely effective on hot water, and it does nothing for heating |
| Smart controls with automation and optimisation | Learning controls with features such as optimum start and away detection | Varies enormously by product. Some deliver a lot; some are a timer with an app |
Weather and load compensation both work by letting the boiler run cooler, which is where a condensing boiler is most efficient. Both require the control and the boiler to actually communicate rather than simply switch. Ask whether the control modulates the boiler – if the answer is no, it cannot deliver compensation whatever else it does.
Why compensation is the one that matters
A condensing boiler recovers latent heat by cooling flue gases enough to condense the water vapour in them. That only happens when the return water temperature is low enough.
A boiler left at its factory flow temperature, switching on and off against a room thermostat, spends much of its life running at return temperatures too high to condense. It is a condensing boiler that is not condensing, and the efficiency figure on the brochure is not being achieved.
Compensation changes that. On a mild day the boiler runs cool; on a cold day it runs hotter. Most of the heating season is mild, so most of the time it runs cool and condenses properly.
There is a secondary benefit that people notice more than the saving: comfort. A compensated system heats gently and continuously rather than blasting and stopping, so the temperature swing in the house is much smaller.
What to ask your installer
- Which measure are you fitting, and why that one? A considered answer is informative.
- Does the control modulate my boiler, or just switch it? The single most important question.
- Does my boiler support OpenTherm or the manufacturer’s own protocol? Compatibility determines what is possible.
- Will compensation actually be configured, or just wired in? Enabling it and setting the curve is a separate step and it is commonly skipped.
- What flow temperature will the boiler be set to? If the answer is the factory maximum, the compensation is not being used.
- Will the system be balanced? Not a Boiler Plus requirement, and it determines whether the heat reaches the far rooms.
The gap between compliance and benefit is real. An installation can satisfy Boiler Plus on paper while the boiler runs at its factory flow temperature and the smart control acts as a timer. That is compliant and it is not what the regulation was for.
Non-combi systems
The additional-measure requirement applies specifically to combis. A system or regular boiler installation must still meet the efficiency standard and have time and temperature control, and there is no fifth-item requirement.
That does not mean compensation is less valuable on a cylinder system – it is just as valuable, and it should be considered on its merits rather than because a regulation names it.
Cylinder systems also have their own control considerations that Boiler Plus does not address: a cylinder thermostat, hot water scheduled separately from heating, and zoning between upstairs and downstairs. Those are worth getting right at the same time.
What Boiler Plus does not cover
- System cleaning and inhibitor, which is a manufacturer’s warranty requirement rather than a regulation – and matters more.
- A magnetic filter, likewise.
- Correct boiler sizing. Boiler Plus sets an efficiency standard; it does not stop an oversized boiler being fitted, and oversizing undermines efficiency regardless.
- Balancing, which determines whether heat reaches the far end of the house.
- Radiator sizing, which determines what flow temperature is achievable.
- Setting the flow temperature sensibly, which is free and frequently not done.
- Actually configuring the control rather than leaving it on defaults.
Which is to say: Boiler Plus is a floor rather than a specification for a good installation. All the things above matter more to how your system actually performs.
Getting a boiler quote? Ask which Boiler Plus measure and why, and whether the control will actually modulate the boiler.
Questions we get asked about this
What is Boiler Plus?
Requirements applying in England since April 2018 covering replacement gas boilers – a minimum efficiency, time and temperature control, and for combis one additional energy efficiency measure from a defined list.
Which additional measure should I choose?
Weather or load compensation, if your boiler supports it. Both work by letting the boiler run cooler, which is where a condensing boiler is most efficient. Flue gas heat recovery helps hot water only.
Does it apply to oil boilers?
Boiler Plus as introduced applied to gas boiler installations in England. The underlying principle – that controls determine efficiency – applies equally to oil, and compensation is just as valuable there.
Is a smart thermostat enough to comply?
Smart controls with automation and optimisation are one of the permitted measures, but products vary enormously. Some genuinely deliver; some are a timer with an app. Whether it modulates the boiler is the useful test.
Does it apply to system and regular boilers?
They must meet the efficiency standard and have time and temperature control. The additional-measure requirement applies specifically to combis.
Can my installation comply and still be inefficient?
Yes, easily. A compliant installation with the boiler left at factory flow temperature, compensation wired but not configured, and an unbalanced system will not deliver what the regulation intended. Compliance is a floor, not a specification.
Regulations and standards referenced on this page
- Approved Document L: conservation of fuel and power (the Boiler Plus measures apply in England) — Ministry of Housing, Communities and Local Government
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