How to choose a radiator installer: questions to ask and red flags

Updated 6 November 2026 · By the Radiator Installation team

Short answer: Choose a radiator installer who sizes radiators to the room rather than guessing, gives a written fixed price that lists the radiators, valves, pipework and inhibitor, and explains how the system will be drained, refilled and balanced. Radiator work itself does not need a Gas Safe engineer, but any work on the boiler or gas supply does, so check registration if the job touches the boiler.

Who is allowed to fit radiators?

Radiators are part of the wet central heating system, so a competent plumber or heating engineer can fit them without being on the Gas Safe Register. The Gas Safe requirement applies to gas appliances, gas pipework and anything touching the boiler's gas side. If the job includes moving, replacing or adjusting the boiler, that part must be done by a Gas Safe registered engineer, and you can check their registration card and the online register.

Fixed electric radiators, electric towel rails and the electrical side of dual-fuel rails should be installed by a competent electrician. In England and Wales some of this work, such as a new circuit or certain work in bathrooms, is notifiable under Part P of the Building Regulations, which a registered electrician can self-certify.

What a good quote should include

Item	What to look for
Radiators	Make or type, size and rated output for each room
Valves	TRVs and lockshields, or reuse of existing valves stated clearly
Pipework	Any alterations, new runs and whether floors are lifted
System work	Draining, refilling, inhibitor and bleeding
Balancing	Whether the system is balanced after fitting
Making good	Filling holes, relaying boards, and what is left for you to decorate
Waste	Whether old radiators are taken away

A clear quote means you can compare like with like. Two prices that look far apart often differ because one includes valves, inhibitor or balancing and the other does not.

Questions to ask before booking

How have you worked out the size of each radiator?
Will you fit new TRVs, and which radiator should not have one?
Is my system sealed or open-vented, and does that change the job?
Will you add inhibitor, and how much?
Will you balance the system afterwards?
What happens if a valve or pipe joint fails while draining down?
How long will the heating and hot water be off?

Red flags to watch for

Recommending sizes without asking about the room, windows or insulation
Refusing to put the price in writing
Pressure to buy a power flush without explaining why it is needed
No mention of refilling with inhibitor
Claiming radiator work needs Gas Safe registration to justify a high price, or the reverse, offering to adjust a boiler without being registered
Asking for the full payment before any work starts

Sizing is where many jobs go wrong

The most common complaint after a radiator job is a room that is still cold. That usually happens when the new radiator was chosen to fit the space rather than to heat the room, or when a designer or chrome radiator with a lower output replaced a plain panel. A good installer will check the output in watts or BTU against the room's needs and tell you if the radiator you like will struggle.

If you are planning a heat pump in the next few years, say so. Sizing radiators for a lower flow temperature now avoids replacing them twice.

Ask to see the output figure for each radiator and the Delta T it is quoted at. Most catalogues quote Delta T50, but some quote Delta T60 or Delta T70, which makes a radiator look more powerful than a rival that is actually the same. A competent installer will compare like with like and explain the numbers without fuss.

Comparing quotes fairly

Prices for radiator work vary more than people expect, and the difference is rarely just profit. One installer may plan to reuse old valves while another replaces them; one may isolate a single radiator while another drains the whole system and adds a full dose of inhibitor; one may include a basic radiator while another prices a better-made model with a longer manufacturer warranty. Line the quotes up item by item before deciding.

Question	Why it matters
Are new valves included?	Old valves often seize or leak once disturbed
Is inhibitor included?	Refilling without it speeds up corrosion and sludge
Is the system balanced?	Unbalanced systems leave some rooms cold
Who supplies the radiators?	Supplying your own can save money but shifts the risk of wrong sizing to you
What if extra work is found?	Seized valves or corroded pipe can add time, so ask how this is priced

If you choose to supply your own radiators, confirm the size, pipe centres and output with the installer before ordering, and check the radiator on delivery for transit damage before the fitting day.

After the job

Before the installer leaves, run the heating and check every radiator heats evenly, that there are no drips at the valves, and that a sealed system is back at its normal cold pressure, usually around 1 to 1.5 bar on the boiler gauge. Ask which valves were set for balancing so they are not changed by accident when decorating.

Keep a note of what was fitted: the radiator make and model, its output, the valves used and how much inhibitor went in. It makes future work quicker, helps if a manufacturer warranty claim is ever needed, and is useful information to pass on if you sell or let the property. Also ask for the manufacturer's paperwork for each radiator, as warranty terms often depend on the system being properly treated.