Why is my towel rail cold when the heating is on?

A cold towel rail is usually one of three things, and the shape of the rail makes the first of them much more likely than on any other radiator in the house.

Safety

What you'll need

• A radiator bleed key
• A small adjustable spanner
• A cloth and a bowl

Step by step

1. Feel where it is cold.Warm at the bottom and cold at the top means air. Cold everywhere means no flow. Cold at the bottom and warm at the top means sludge. The pattern tells you which problem you have.
2. Bleed it first.Bleed valve at the top, key a quarter turn with a cloth underneath, and wait for the hiss to become water. Towel rails have horizontal bars that trap air at every level, so they need bleeding more often than anything else.
3. Bleed it more than once.Air often sits in several bars. Run the heating for half an hour and bleed again — a second or third pass frequently gets more out.
4. Check both valves are open.One end has a TRV or a manual valve, the other a lockshield. A lockshield closed during decorating and never reopened is a very common cause.
5. Open the lockshield properly.Pull the cap off and open it with a spanner. If it was closed, open it a turn or two, then rebalance once the rail heats.
6. Check the TRV pin is not stuck.Take the head off. The pin underneath should spring back when pressed. Stuck down means closed — free it with gentle taps and a little penetrating oil, or replace the head.
7. Establish whether it is dual fuel.Many bathroom rails have an electric element as well as the heating connection, so they can run in summer. If it is cold in winter with the heating on, that is a plumbing issue; cold in summer with everything off is simply the element being switched off.
8. Check the element and its switch.On a dual fuel or electric rail, find the fused spur or switch, which is often outside the bathroom door. A tripped fuse there explains a permanently cold rail.
9. Check it is on the right circuit.Towel rails are sometimes plumbed to the hot water rather than the heating circuit, in which case it heats when the water heats, not when the heating runs. That is by design rather than a fault.
10. Look at the rest of the house.If several radiators are poor, the problem is the system rather than the rail — pressure, pump or a boiler fault. One cold rail among warm radiators is a local problem.
11. Check the system pressure.On a sealed system the gauge should read 1.0 to 1.5 bar cold. Low pressure starves the highest points first, and a bathroom rail upstairs is often the highest point in the house.
12. Consider sludge if bleeding does nothing.Cold at the bottom with a warm top means magnetite settling in the lower bars. Flushing or a chemical cleanse is the answer, and a magnetic filter prevents it returning.
13. Bleed again after any work.Anything that lets air into the system puts it straight back into the towel rail, because it is usually the highest point.

Tips

• Bleed it two or three times. The horizontal bars trap air in several places at once.
• Check the lockshield. Closed during decorating and forgotten is a very common cause.
• A rail that is cold in summer but fine in winter is a dual fuel element that is switched off, not a fault.

Common mistakes

• Bleeding once and assuming it is done — A towel rail's shape traps air in multiple bars. One bleed usually releases some but not all of it, and the rail stays partly cold.
• Switching on an electric element in a drained rail — The element relies on the fluid around it to carry heat away. Run dry, it burns out within minutes and cannot be repaired.

If it doesn't work

Questions people ask