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How to fill an Electric Heated Towel Rail
Many people are uncertain about whether their new electric heated towel rail needs filling and if so, how to do it safely. This confusion is understandable as some towel rails come pre-filled, others arrive empty. If you're reading this article then it's probably because you've purchased an electric radiator that has not arrived pre-filled and you're wondering what the process is.
Before diving into it, it’s important to make it clear that working with electrics in a bathroom is never a DIY task. While we’ll explain what filling involves so you understand what’s happening, this is ultimately a job for a qualified professional.
- Further reading: Can You Put an Electric Radiator in a Bathroom?
Table of Contents
Pre-filled vs empty electric towel rails
Most modern electric towel rails come ready-filled with a special fluid and are sealed in the factory. These require no additional filling by the homeowner. The vast majority of electric towel rails at Trade Radiators come pre-filled. Some models are ocassionally supplied unfilled, which means the installer must fill them before fitting the heating element.
If you have an empty towel rail that requires filling, then it's worth remembering that bathrooms are high-risk environments. Any electrical connection must comply with strict safety regulations, including Part P of the Building Regulations in England and Wales.
A qualified electrician will:
- Wire the element safely into the mains.
- Position the appliance in the correct bathroom zone (the legally defined safe distance from water sources).
- Ensure the towel rail is correctly filled and free of airlocks.
Attempting this yourself risks electrical shock, leaks, or a failed installation.
What does filling an electric towel rail mean?
Electric towel rails don’t use your central heating system. Instead, they are sealed units containing a heat-transfer liquid. The internal element heats this fluid, which then warms the rail and the surrounding air.
The filling usually consists of:
- Deionised water, which is free from minerals that cause limescale or corrosion.
- Corrosion inhibitor which protects the internal metal surfaces from rust.
- Occasionally Glycol or antifreeze which can improve heat transfer and prevent freezing.
Filling is an important part of how an electric towel rail works. Without liquid inside, the heating element would quickly overheat and fail, leaving the appliance unusable. The liquid acts as a medium, carrying the heat from the element throughout the rail so it can warm both the metal surface and the surrounding air evenly. A correct mixture also ensures efficient, consistent performance and protects the internal components from unnecessary strain.
It’s equally important to avoid using the wrong kind of liquid. For example, ordinary tap water contains minerals that can lead to limescale, sludge, and internal corrosion, all of which reduce efficiency and shorten the lifespan of the rail. For this reason, most homeowners prefer to buy pre-filled towel rails. These come sealed at the factory with the correct fluid mixture already in place, eliminating the guesswork and guaranteeing safe, reliable operation from the start.
What does filling an electric towel rail mean?
When an electric towel rail does require filling, the process involves more than simply pouring in water. A qualified installer knows how to prepare the correct fluid mixture, which is usually a blend of deionised water and corrosion inhibitor, to protect the rail’s internal surfaces and ensure long-term reliability. They’ll also leave a small expansion gap at the top of the radiator so the liquid has room to expand as it heats, preventing unnecessary pressure build-up.
Another important step is bleeding the rail to remove any trapped air pockets, which could otherwise reduce efficiency or stop the rail heating properly. Finally, the element must be hardwired into a fused spur outlet, as standard plugs and sockets are not permitted within bathroom zones. These steps are small but vital, and they highlight why this is not a DIY task. Getting any one of them wrong risks poor performance at best, and at worst could create serious safety hazards.
- Further reading: The Best Electric Radiators
The filling process
To give you an idea of what’s involved, here’s what an electrician or heating engineer will typically do:
- Preparation
Position the towel rail securely on the wall, leaving access to the filling point at the top. - Mixing the solution
Combine deionised water with corrosion inhibitor (and antifreeze if needed). - Filling
Pour the solution in slowly until the rail is nearly full, leaving a small air gap. - Bleeding
Open the air vent at the top to release trapped air bubbles. - Sealing
Close the vent securely, check for leaks, and wipe down connections. - Electrical connection
Wire the heating element into a fused spur outside the bathroom zones.
Filling FAQs
▸ Do all electric towel rails need to be filled?
No. Most modern electric towel rails are supplied pre-filled with a specialist heat-transfer fluid and are ready for a qualified electrician to install. Only “dry” or conversion kits (where a standard towel rail is converted for electric use) typically require filling during installation.
▸ How can I tell if my towel rail is pre-filled or needs fluid?
Check the product listing or installation manual. Pre-filled models are clearly labelled and often feel heavy out of the box. If the instructions describe adding fluid or state “dry/empty,” it requires filling during installation by a professional.
▸ What fluid goes inside an electric towel rail?
Typically deionised (or demineralised) water combined with a corrosion inhibitor formulated for heating systems. Some products use a specific premix (e.g., glycol-based) supplied by the manufacturer. Always follow the rail/element manufacturer’s specification.
▸ Why can’t I use tap water?
Tap water contains minerals that cause limescale, sludge and corrosion, leading to poor performance, noise and premature failure. Deionised water with inhibitor protects internal metal surfaces and keeps heat transfer efficient over time.
▸ Do I need antifreeze (glycol) in the mix?
Only if the manufacturer specifies it or the rail is installed in an area at risk of freezing (e.g., unheated outbuilding). Use the exact product and concentration recommended in the instructions to avoid viscosity and performance issues.
▸ Who should fill and wire an electric towel rail?
A qualified electrician must carry out the work. Bathroom electrics are controlled by regulations; the rail must be hardwired to a fused spur in an appropriate bathroom zone with the correct IP rating. This is not a DIY task.
▸ What is an “expansion gap” and why is it important?
Installers leave a small air space at the top of the rail so the fluid can expand as it heats. Without this gap, pressure can build, risking leaks or damage. The size of the gap is given in the manufacturer’s instructions.
▸ How full should an electric towel rail be?
Usually “almost full,” leaving the specified expansion gap (often a few centimetres from the highest point). The exact fill level varies by model so follow the filling guide supplied with your rail and element kit.
▸ What happens if I overfill the towel rail?
Overfilling removes the expansion space, which can cause pressure build-up, weeping at connections, or safety cut-outs tripping. An installer will drain a little fluid to restore the correct level and bleed out trapped air if needed.
▸ Do electric towel rails need bleeding like central heating radiators?
Yes. After filling, the installer will bleed trapped air so the element is fully immersed and heat circulates evenly. Once commissioned correctly, frequent bleeding is not usually required unless the rail has been drained or moved.
▸ My rail is humming or gurgling. Does it need more fluid?
Noises often indicate trapped air or an incorrect fill level. Switch off power and contact your installer or a qualified electrician to bleed and check the fluid level. Do not open the rail yourself if it is hardwired and live.
▸ Can I top up the fluid myself if the level looks low?
Not recommended. Topping up with the wrong fluid or losing the expansion gap can cause damage or create a safety risk. Have a qualified professional diagnose the cause of any loss and refill to the correct specification if required.
▸ What IP rating does an electric towel rail need in a bathroom?
It depends on the bathroom zone. Your electrician will select a rail/element with a suitable IP rating (e.g., IPX4/IP44 or higher) and position it in a compliant zone relative to baths, showers and basins. Always follow the latest regulations and manufacturer guidance.
▸ Do electric towel rails plug in?
No.Bathroom models must be hardwired to a fused spur by a qualified electrician. Standard plug-and-socket connections are not permitted within bathroom zones for safety reasons.
▸ What’s the difference between pre-filled and “dry” electric rails?
Pre-filled rails arrive charged with the correct heat-transfer fluid: the electrician mounts and wires them. “Dry” conversions use a standard (hydronic) rail fitted with an electric element and filled on-site to the specified level with the correct fluid mix.
▸ Will filling affect my warranty?
It can if done incorrectly or with non-approved fluids. To keep warranties valid, use a qualified installer, follow the manufacturer’s instructions, and retain commissioning paperwork and invoices as proof of professional installation.
▸ Are electric towel rails expensive to run?
Electricity costs more per unit than gas, but rails are efficient for targeted use. Timers and thermostats minimise energy use, which is ideal for warm towels in the morning or evening without heating the whole home. Choose a wattage appropriate for your room size and usage pattern.
▸ Can an electric towel rail heat the whole bathroom?
Often, yes, if sized correctly. Check the room’s heat requirement (in Watts) and choose a rail with sufficient output. For large or poorly insulated bathrooms, consider a higher-wattage rail or an additional heat source for comfort on cold days.
▸ What is a dual fuel towel rail and does it need filling?
Dual fuel rails work on your central heating in winter and switch to electric in warmer months. The rail contains liquid either way, so correct fluid level and inhibitor are important. A professional will fill/commission it and wire the electric element safely.
Further reading: A Complete Guide to Dual Fuel Heating
▸ How long does an electric towel rail take to heat up?
Typically 10–30 minutes to feel warm, depending on wattage, size and room temperature. Using a programmable timer lets you pre-warm towels for when you need them and avoids wasting energy when you don’t.
- Further reading: A Complete Guide to Electric Heating
Helpful videos
Electric heated towel rails at TradeRadiators.com
When it comes to selecting the perfect electric towel rail, there’s more to think about than just size or finish. The right model should balance performance, efficiency, and style while suiting the unique layout of your bathroom. At Trade Radiators, we offer one of the UK’s widest ranges of electric and dual fuel towel rails, from sleek chrome ladder styles to modern matt black finishes and classic white options. Whatever your décor or heating requirements, you’ll find something that not only keeps your towels toasty but also enhances your bathroom’s look and feel.
To help inspire your choice, we’ve included a selection of images below showcasing real customer installations. These examples highlight how versatile electric towel rails can be, whether used as a subtle addition in a compact en-suite or as a striking centrepiece in a family bathroom. Browse the gallery to see how others have transformed their spaces, and then explore our full Trade Radiators collection to find the perfect rail for your own home.
