Domakihub How to Replace a Radiator Valve Safely and Quickly
A clear, step-by-step guide for homeowners, landlords, and property managers in Greece.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A faulty or leaking radiator valve is one of the most common heating problems in Greek homes, holiday rentals, and hotels — and it is a repair most property owners can handle themselves. The video above walks you through the full replacement process visually, while this guide breaks it down into clear, ordered steps with the practical context you need before you pick up a wrench. Whether your valve is dripping, stuck shut, or simply past its lifespan, replacing it promptly keeps your central heating running efficiently and protects floors and walls from water damage.
Why Radiator Valves Fail
Radiator valves — particularly thermostatic radiator valves (TRVs) — contain small rubber seals and a metal spindle that degrade over time. In Greece, properties that sit unoccupied for months between rental seasons are especially vulnerable: the spindle can seize in the closed position, and seals dry out and begin to weep water around the gland nut. Limescale in hard-water areas such as Athens and the Aegean islands accelerates this wear.
A leaking valve is not just a nuisance. Persistent drips corrode the valve body and the radiator tail, cause damp patches on skirting boards, and reduce system pressure — all of which can lead to more expensive repairs if left unattended.
Tools and Parts You Will Need
Before you start, gather: two adjustable spanners (one 24 mm, one 15 mm), PTFE tape, a radiator bleed key, two towels or a small tray, a bucket, and the replacement valve. Measure the existing valve connection size — most Greek domestic systems use a 15 mm or half-inch (½") compression fitting. If you are fitting a TRV, also check that the new valve head is compatible with your radiator tail (straight or angled).
For most jobs you do not need to drain the entire central heating system. You will only need to isolate the single radiator by closing both valves (flow and lockshield), then drain just that radiator — a far quicker approach.
How to Replace a Radiator Valve: 5 Steps
- 1
Isolate and drain the radiator
Close the existing thermostatic or manual valve on the flow side by turning it fully clockwise. On the opposite end, remove the plastic cap from the lockshield valve and close it fully with an adjustable spanner, counting the turns so you can reopen it to the same position later. Place towels and a bucket below the valve you are replacing, then open the bleed valve at the top of the radiator with a bleed key to release pressure and let water drain down into the bucket through the loosened valve connection.
- 2
Remove the old valve
Use one spanner to hold the radiator tail steady and a second spanner to loosen the union nut that connects the valve to the tail. Unscrew slowly — a small amount of water will drain out, so keep the bucket in place. Once the union nut is fully loose, slide the old valve off the pipe. If the pipe olive (the small copper ring that makes the seal) is in good condition, leave it in place; if it is cracked or deformed, cut it off carefully and fit a new one before proceeding.
- 3
Prepare the fittings
Clean the threads on the radiator tail and on the pipe end with a dry cloth. Wrap PTFE tape clockwise around the male thread on the radiator tail — three or four overlapping turns is sufficient. This tape compresses into the thread and creates a watertight seal without requiring sealant compound. If the new valve comes with a new olive or fibre washer, use it rather than reusing the original one.
- 4
Fit and hand-tighten the new valve
Slide the new valve onto the pipe, making sure it is oriented correctly (the flow arrow on the valve body should point in the direction of flow — usually upward from the pipe). Thread the union nut onto the radiator tail by hand first to avoid cross-threading, then tighten with two spanners: hold the valve body still with one spanner and tighten the union nut with the other. Firm hand-spanner pressure is enough — over-tightening can crack the valve body or damage the olive.
- 5
Refill, bleed, and check for leaks
Reopen the lockshield valve the exact number of turns you counted when closing it, then open the new valve to your desired setting. Water will begin to refill the radiator. Hold the bleed key ready and open the bleed valve at the top of the radiator until water (not air) runs out steadily, then close it. Wipe all joints dry and watch for ten minutes with the heating on. If you see any weeping at the union nut, give it a quarter-turn more with the spanner. Top up the system pressure at the filling loop if needed — most systems should read between 1.0 and 1.5 bar cold.
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FAQ
- Do I need to drain the whole heating system to replace one radiator valve?
- No. If both the flow valve and the lockshield valve on the same radiator are working and can be closed, you only need to isolate and drain that single radiator. This saves a significant amount of time and means you do not have to refill and re-pressurise the entire system from scratch.
- How do I know whether to fit a thermostatic valve (TRV) or a standard manual valve?
- A TRV gives you room-by-room temperature control, which saves energy and is particularly useful in holiday rentals where different rooms may be occupied at different times. Manual valves are simpler and less expensive, and are a good choice for hallways, bathrooms, or rooms where a constant low level of heat is preferred. In either case, do not fit a TRV in the same room as the central thermostat, as the two controls will conflict.
- My new valve is dripping from the gland nut, not the union nut — what should I do?
- A drip from the gland nut (the nut around the spindle shaft, not the pipe connection) usually means the internal packing has dried out or is loose. Try tightening the gland nut by a quarter-turn with a spanner. If it continues to leak, the valve may need a new gland packing kit, or the valve itself should be replaced — this is often a sign of an old or low-quality valve.