Regulations · 4 min read · Updated 6 November 2026
Radiators and Building Regulations: what Part L means for you in 2026
Why Building Regulations come up with radiators
Most people never think about Building Regulations when they replace a radiator, and for a simple swap that is usually fine. But the 2021 edition of Approved Document L, which applied to most work in England from 15 June 2022, changed what is expected whenever heating systems are installed or significantly altered. Wales and Scotland have their own equivalent rules, so details differ if you live there.
The aim of the changes is to cut energy use and get homes ready for low-carbon heating. That means lower flow temperatures, better controls and properly commissioned systems. Radiators are central to all three, so it helps to know where your job sits.
Which radiator jobs need sign-off and which do not
The table below is a general guide for England. Your local building control body has the final say, and a heating engineer should tell you if your job crosses into notifiable territory.
| Job | Notifiable under Building Regulations? |
|---|---|
| Like-for-like radiator swap on the same pipework | Not normally |
| Adding a radiator to an existing system | Not normally |
| Moving a radiator to another wall | Not normally |
| Replacing the boiler or other heat source | Yes, usually self-certified by a registered installer |
| Installing a whole new wet heating system | Yes |
| Installing a heat pump with new radiators | Yes, usually self-certified via a competent person scheme |
| New electric towel rail on a new circuit or in a bathroom zone | Electrical work may be notifiable under Part P |
Not being notifiable does not mean anything goes. Work still has to be done safely and to a reasonable standard, and if you sell the house a buyer's surveyor may ask questions about obviously poor alterations.
What Part L 2021 asks for on heating systems
When a new or replacement wet heating system is installed, or the heat generator is replaced, the guidance expects several things. These are the points that matter most for radiators:
- The system should be designed so the flow temperature does not exceed 55°C, which often means larger radiators or more emitters than an old high-temperature system
- Each room should normally have its own temperature control, usually thermostatic radiator valves, except where the room has the main room thermostat
- The system should be commissioned, balanced and the details handed to the householder
- Water treatment should be carried out to protect the system, in line with the industry standard BS 7593
The 55°C rule applies to the design of new and replacement systems. If you are only swapping a single radiator, nobody will insist the rest of the house is redesigned. But it is worth asking your installer to size any new radiator so it will still heat the room well at a lower flow temperature, because that is the direction the rules are heading.
TRVs: when they are expected
Thermostatic radiator valves sense the room temperature and cut the flow to that radiator when the room is warm enough. Under the current guidance, when a boiler is replaced each room should normally be fitted with TRVs or equivalent zone controls, unless it is the room with the main thermostat. A bypass or automatic bypass valve may be needed so the boiler always has a flow path.
For a single radiator swap, fitting new TRVs is not a legal requirement in most cases, but it is usually sensible. Old valves are often seized, weeping or impossible to isolate, and the cost difference of fitting new valves at the same time is small compared with a separate visit later.
Electrical rules for electric radiators and towel rails
Plumbed radiators sit outside the electrical rules, but electric radiators and electric or dual-fuel towel rails do not. In England, Part P covers electrical safety in homes. Installing a new circuit, replacing a consumer unit, or adding to a circuit in a room with a bath or shower is generally notifiable. A registered electrician can self-certify the work and give you a certificate.
Bathrooms are divided into zones around the bath and shower, and the zone dictates what can be fitted where and what protection, such as RCD protection, is needed. If a towel rail element is going in near a shower, get an electrician involved from the start.
Gas Safe and who can do the work
You do not need a Gas Safe registered engineer to replace or add a radiator, because the work is on the water side of the system and does not touch gas pipework or the boiler. You do need a Gas Safe engineer for any work on a gas boiler, including replacing it, moving it or altering its flue.
If radiator work is part of a bigger job that includes a new boiler, the boiler installer will usually register the work with building control through their competent person scheme and give you a compliance certificate. Keep it with your house paperwork, because conveyancers often ask for it.
Practical checklist before you start
- Check whether the boiler or heat source is also being changed, because that triggers the main Part L duties
- Ask for new radiators to be sized for a lower flow temperature where practical
- Fit TRVs on new radiators unless it is the room with the main thermostat
- Ask for inhibitor to be added after the system is refilled
- If there is any electrical work, confirm who will certify it
- Keep receipts, model numbers and any certificates together
Frequently asked questions
Do I need building control approval to replace a radiator?
Usually not. Replacing or adding a radiator on an existing wet central heating system is not normally notifiable in England. Building Regulations duties become relevant when the whole system or the boiler is replaced, or when electrical work such as a new circuit for an electric towel rail is involved. If in doubt, your local building control team can confirm before work starts.
Does the 55°C flow temperature rule mean my radiators must be replaced?
No. The 55°C maximum flow temperature applies to the design of new and replacement heating systems, not to every home with existing radiators. When a boiler is replaced, the installer should consider it, which can mean upsizing some radiators. For a single radiator swap, it is simply good practice to choose a size that will still heat the room at lower temperatures.
Are TRVs a legal requirement?
TRVs or equivalent room-by-room controls are expected under Part L when a heating system is installed or the boiler is replaced, except in the room with the main thermostat. For a one-off radiator swap they are not usually required, but fitting them at the same time is normally cheap and gives you better control over room temperatures and running costs.
building regulations Part L TRVs compliance
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