Domakihub How to Install a Radiator: Save Money on Your Heating Bill
A clear, practical guide to fitting a new radiator to your central heating system.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Fitting a new radiator is one of the most rewarding DIY plumbing jobs you can tackle in a Greek home, holiday apartment, or hotel room — it can dramatically improve a cold corner at a fraction of the cost of calling a heating engineer. The video above walks you through the process visually, while this guide breaks every stage into clear, ordered steps so you can plan the work, gather the right materials, and avoid the most common mistakes. Whether you are replacing a tired old panel or adding heating to a newly finished room, the process is straightforward if you work methodically.
What You Need Before You Start
Gather your materials before draining anything down. You will need a new radiator and a matching pair of thermostatic radiator valves (TRVs), two radiator brackets (usually supplied with the radiator), PTFE tape, a radiator bleeding key, pipe cutters, push-fit or compression fittings, and a central-heating inhibitor to top up the system afterwards. A spirit level, pencil, tape measure, hammer drill with a 7 mm masonry bit, and wall plugs complete the toolkit.
Greek buildings frequently use 15 mm copper or PEX pipe, but older properties — especially in Thessaloniki or Attica — sometimes run 22 mm flow-and-return pipes. Check your existing pipework diameter before buying valves, because mismatched fittings are the single most common source of delays on this job.
Understanding the Central Heating Circuit
A standard two-pipe central heating system has a flow pipe (hot water from the boiler) and a return pipe (cooled water heading back). The new radiator connects across both. The thermostatic valve goes on the flow side; the lockshield valve goes on the return side and is used to balance the system — that is, to ensure each radiator in the building receives a proportional share of the pump's output.
In holiday rentals and small hotels with multiple zones, always identify which zone circuit you are tapping into before cutting pipe. Shutting down the wrong zone while guests are using hot water in another wing is an avoidable headache.
How to Install a Radiator: 5 Steps
- 1
Drain Down the Relevant Circuit
Turn off the boiler and let the system cool. Attach a hose to the drain-off valve (usually near the bottom of the main flow pipe or next to the boiler) and run it to a drain outside or into a bucket. Open the drain valve and crack the bleed valves on the highest radiators in the system to let air in — this breaks the vacuum and allows the water to flow out quickly. Collect and dispose of the inhibitor-rich water responsibly; do not pour large volumes onto planted areas.
- 2
Mount the Radiator Brackets on the Wall
Measure the wall space and mark the centre point. Hold the radiator against the wall at the correct height — the bottom of the panel should sit at least 100 mm above the floor to allow good air circulation. Mark the bracket positions using a spirit level to ensure both are perfectly horizontal. Drill into the masonry with a 7 mm bit, insert wall plugs, and screw the brackets firmly in place. Hang the radiator onto the brackets and confirm it sits level before proceeding.
- 3
Fit the Radiator Valves and Tail Pieces
Wrap PTFE tape clockwise around the threaded tail pieces 15 to 20 times before screwing them into the bottom ports of the radiator — hand-tight first, then firm with a spanner. Attach the thermostatic radiator valve body to the flow-side tail and the lockshield valve body to the return-side tail. Do not overtighten; radiator tails are typically made of brass and the threads can strip if forced.
- 4
Connect the Pipework
Cut the existing flow and return pipes cleanly with a pipe cutter (never a hacksaw, which leaves burrs). Insert a tee fitting into each pipe run to create the branch that feeds the new radiator. Run short lengths of pipe from each tee up to the valve connections, keeping the runs as straight as possible to minimise flow resistance. Use compression or push-fit fittings appropriate to your pipe material. If the new radiator is in a different position from the old one, lift the relevant floorboards to re-route the branches neatly under the floor.
- 5
Refill, Bleed, and Balance
Close the drain valve and remove the hose. Slowly open the system's fill loop (or top up via the feed-and-expansion tank on older open-vented systems) until the pressure gauge reads 1.0 to 1.5 bar. Work around the building bleeding every radiator with the bleed key until only water — no air — escapes each bleed point. Restore the boiler to normal operation and let the system reach full temperature. Then set each lockshield valve: start fully open on the radiator nearest the boiler and progressively close lockshields on closer radiators until every panel in the building reaches a similar temperature. Finally, add a full dose of central-heating inhibitor through the feed point to protect against corrosion.
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FAQ
- Do I need a licensed plumber to install a radiator in Greece?
- Greek law requires a licensed installer (εγκαταστάτης υδραυλικός) for any work on a shared building system or for gas-related modifications. Fitting an additional radiator to an existing sealed hot-water circuit in a privately owned property is generally a grey area, but if the work involves touching a communal riser or requires a permit (e.g., in a hotel), you must use a licensed professional. When in doubt, get a qualified plumber to do the final connection and sign off the work.
- How do I know what size radiator I need for a room?
- A rough rule of thumb is 100 watts of radiator output per square metre of floor space in a well-insulated room, rising to 130–150 watts per square metre in older, less insulated Greek stone or concrete buildings. Most radiator manufacturers publish BTU/watt output tables for their panels. Measure the room in metres, multiply length by width, and multiply the result by your chosen watt-per-m² figure. Round up to the next available panel size rather than down.
- Why is my new radiator cold at the top after installation?
- A radiator that is warm at the bottom but cold at the top almost always contains trapped air. Use a bleed key to open the bleed valve at the top corner of the panel (keep a cloth ready) until water trickles out steadily, then close the valve. If the problem recurs within days, the system may be generating hydrogen gas through corrosion — a sign that the inhibitor level is too low or that the system contains dissimilar metals reacting together.