How to Install a Radiator — Step-by-Step UK Guide

What You'll Need

Before You Start

• Calculate the heat output required for the room — use our Radiator Sizing Calculator and Radiator BTU Calculator.
• Choose a radiator with a BTU output that matches or slightly exceeds the room's heat loss.
• Plan your pipe route from the existing pipework to the new radiator position. Under-floor routes are neatest but require lifting floorboards.
• Turn off the boiler and allow the system to cool before starting any work.
• Check for hidden pipes and cables in the wall before drilling — use a pipe and cable detector.

Step-by-Step Instructions

Step 1: Mark the Bracket Positions

Hold the radiator against the wall in the desired position (at least 100mm above the floor, ideally under a window). Use the manufacturer's bracket template to mark drilling points. Check the marks are level with a spirit level.

Step 2: Fix the Brackets

Drill into the wall using a masonry bit. Insert wall plugs and screw the brackets in firmly. Double-check they are level — a poorly hung radiator will not bleed properly because air cannot reach the bleed valve.

Step 3: Fit the Valves

Wrap PTFE tape around the valve tail threads (5-6 turns, clockwise). Screw the valve tails into the radiator — TRV on the flow side (usually the side the pipe enters from the boiler) and lockshield on the return. Tighten with a spanner. Fit the bleed valve at the top and blanking plug on the opposite side.

Step 4: Hang the Radiator

Lift the radiator onto the wall brackets. It should sit securely on both brackets. Check it is level and adjust brackets if necessary.

Step 5: Run the Pipework

Connect 15mm copper pipe from the existing flow and return pipes to the radiator valve connections. Use compression fittings for ease or solder (Yorkshire) fittings for a neater finish. Ensure the pipe is clipped at regular intervals (every 1.2m for horizontal runs, 1.8m for vertical).

Step 6: Connect to the Valves

Tighten the compression nuts on each valve. Use two spanners — one to hold the valve body, one to tighten the nut. Do not over-tighten or you risk cracking the olive or valve body.

Step 7: Fill and Bleed

Open both valves fully and repressurise the system to 1.0-1.5 bar (check your boiler manual). Turn the heating on and allow the system to warm up. Bleed the new radiator using the bleed key until a steady stream of water comes out, then close the bleed valve.

Step 8: Check for Leaks

Carefully inspect every joint — both valve connections, compression fittings and any solder joints. Run tissue paper around each connection. Even a slight dampness indicates a leak that needs attention. Tighten gently or remake the joint.

Step 9: Balance the System

Once all radiators are hot, balance the system by adjusting lockshield valves. The radiator nearest the boiler should have its lockshield valve partly closed so that distant radiators receive adequate flow. Aim for a 12°C temperature difference between flow and return on each radiator.

Step 10: Add Inhibitor

Add a dose of corrosion inhibitor (e.g. Fernox F1 or Sentinel X100) to the system via the filling loop or a radiator bleed point. This protects against internal corrosion and sludge build-up.

Common Mistakes to Avoid

• Wrong size radiator: An undersized radiator will not heat the room. Always calculate BTU requirements first.
• Brackets not level: An unlevel radiator traps air in the wrong place and cannot be bled properly.
• Over-tightening compression fittings: Over-tightening crushes the olive and causes leaks. Finger-tight plus one to one-and-a-quarter turns with a spanner is usually sufficient.
• Forgetting inhibitor: A system without inhibitor corrodes internally, creating sludge that blocks radiators and damages the boiler.
• Not balancing: An unbalanced system means radiators near the boiler get too hot while distant ones stay cold.

Cost Estimate (2026 UK Prices)

Use our Radiator Sizing Calculator and Radiator BTU Calculator to ensure you choose the right radiator for your room.