How to bleed a towel rail, and why it may still be cold

Why towel rails get air in them more than radiators

Air in a heating system collects at the highest points. A towel rail is tall and narrow, often the tallest heat emitter in the house, and it is frequently fitted in a top-floor bathroom or a loft conversion. That combination means it traps more air than an ordinary radiator and is usually the first thing to go cold at the top.

The first time the heating comes on in autumn is when most people notice. Air that has gathered over the summer shows up as soon as the pump starts moving water again. The classic sign is a rail that is warm across the lower bars and cold across the top ones. You might also hear gurgling in the rail or its pipes when the heating first starts.

Check what kind of towel rail you have first

Before you open anything, make sure the rail is actually on the heating system. Look at the bottom of the rail. If there are two pipes coming out of the floor or wall with a valve on each, it is plumbed into the central heating and can be bled. If there is only a cable running to a switched spur on the wall, it is electric only. Electric rails are filled with fluid and sealed at the factory, so opening a bleed point on one lets out fluid that cannot be replaced at home.

Dual fuel rails have both: pipes and valves, plus an electric heating element screwed into the bottom of one bar with a cable to a spur. These can be bled like a normal rail, but switch the electric element off first and leave it off until the rail is full of water again. An element run in a rail that has been partly drained can burn out. Our guide to choosing a towel rail for central heating or electric explains how the three types differ.

What you need

The bleed valve on most towel rails takes a standard radiator key. Some designer and chrome rails use a small slotted screw or an Allen key instead, and a few have the bleed point hidden under a decorative cap on the top of one upright, which pulls or unscrews off.

• A radiator key, flat-bladed screwdriver or small Allen key, to suit the valve
• An old towel or cloth to wrap around the valve
• A small container for drips
• Access to the boiler pressure gauge and filling loop, if you have a sealed system

How to bleed a towel rail: the steps

Work with the system cool. Hot water can spray out of the valve, and a hot system is under slightly more pressure, which pushes water out faster.

• Turn the heating off at the programmer or thermostat and wait until the rail is cool to touch
• If it is a dual fuel rail, switch off the electric element at its spur
• Find the bleed valve at the top of one upright and fit the key or screwdriver
• Hold a cloth tightly around and under the valve
• Turn the key slowly anticlockwise about a quarter of a turn, no more than half a turn
• Let the air hiss out, and close the valve as soon as a steady trickle of water appears
• Wipe up any drips and check the valve is closed and not weeping
• Check the boiler pressure gauge and top it up if needed
• Turn the heating back on and check the rail heats all the way to the top

Never open the valve more than half a turn. On some rails the bleed pin can come out entirely, and it is hard to refit against running water.

Topping up the boiler pressure afterwards

Most modern homes with a combi or system boiler have a sealed heating system. Every time you let air out, a little pressure goes with it, and a towel rail often needs more bleeding than a single radiator. After you have finished, look at the pressure gauge on the boiler. When the system is cold, most manufacturers want it between 1 and 1.5 bar.

If it has dropped below 1 bar, top it up using the filling loop, the braided hose or key-operated valve under the boiler, following your boiler's instructions. Open it slowly and close it as soon as the needle reaches the right level. Our guides on how to bleed a radiator and on a boiler losing pressure cover this in more detail. If you have an older open vented system with a small tank in the loft, it refills itself and there is no gauge to check.

Towel rail still not heating up?

If bleeding releases no air, or the rail is still cold after bleeding, the problem is something else. The pattern of heat tells you where to look.

Valves, balancing and sludge

Towel rails usually have two valves at the bottom. One may be a thermostatic valve with a numbered head and the other a lockshield with a plain cap. If a valve was closed to take the rail off the wall for decorating and never reopened, the rail stays cold however often you bleed it. If the TRV pin has stuck down over summer, take the head off and gently free it. Our guide to a lockshield valve explains how to check it is open without upsetting the balance.

Because towel rails are often the last emitter on the pipe run, the rest of the system can take all the flow. Balancing the radiators, by turning down the lockshields on the ones nearest the boiler, pushes more hot water to the rail. If the bottom bars stay cold even with good flow, sludge has settled there, which points to the system needing a clean and an inhibitor top-up.

If the rail has to be bled every week, air is getting in somewhere or gas is forming in the system. That needs an engineer to find the cause rather than more bleeding.

When to call a plumber

Call us if the bleed valve is seized or leaking, the rail stays cold after bleeding and checking the valves, the rail needs bleeding over and over, or the boiler pressure will not stay up. Loyal Plumbers repairs radiators, towel rails and central heating across London and everywhere inside the M25, with 10 vans working 24 hours a day and Gas Safe registered engineers for any work on the boiler. Our call-out charge is £60.

When you get in touch, tell us whether the rail is on the heating, electric or dual fuel, which part stays cold and the pressure reading on the boiler. If you are thinking of replacing the rail altogether, our radiator repair and replacement page covers that too.