How to Get Rid of Rust on a Radiator

Rust on a radiator usually starts as a few orange spots where the enamel's chipped, then spreads under the paint until the whole bottom edge looks tired. The good news is that surface rust on a steel or cast iron radiator is easy to stop: brush it back, convert what's left with a rust converter like Rust Halt™ Rust Converter Gel Spray, and repaint. The bad news is that rust can also be the first sign of a leak, and no treatment fixes that. Here's how to tell which one you've got, and how to deal with it properly.

Why do radiators and towel rails go rusty?

A radiator is a thin steel panel with a coat of enamel on it. As long as the enamel is intact, the steel underneath stays dry. Once it's chipped by a hoover, a door or a knock during decorating, moisture gets in and the steel starts to oxidise. In a bathroom it's worse: steam condenses on the coldest surfaces in the room, and a towel rail or radiator that's off for half the day is often one of them.

The other common culprit is the valves. A slow weep from a valve, a bleed screw or a joint keeps the metal around it permanently damp, and you'll see rust tracking down from that point.

Surface rust or a leak? Check this first

Before you treat anything, work out what's actually going on. Surface rust is cosmetic. A leak isn't.

• Surface rust: dry orange or brown patches, flaking enamel, rough spots along the bottom edge or around the brackets. The metal underneath is solid.
• A leak: damp patches, drips, crusty white or green deposits, water marks on the floor, or rust that's always wet around a valve or seam.
• Pinholes: tiny holes along the bottom of a panel, often with a bead of water. That's corrosion from the inside, caused by sludge in the system. The radiator needs replacing.

How to treat surface rust on a radiator

If the metal's sound, this is a morning's work. The radiator must be cold, so turn the heating off and give it an hour.

1. Protect the area. Lay a dust sheet, and mask the wall, the valves and the floor around the radiator.
2. Brush off the loose rust. A wire brush or coarse abrasive pad will take off flaking enamel and loose rust. You don't need to get back to bright metal; you just want the loose, crumbly stuff gone.
3. Degrease. Wipe it down to get rid of dust and any grease, then let it dry.
4. Apply the rust converter. Spray Rust Halt straight onto the rusty areas. It's a gel, so it clings to the vertical face of the radiator instead of running down onto the floor. Two thin coats work better than one heavy one.
5. Let it convert. The rust turns black in about 20 minutes as it converts to iron phosphate. Leave it to dry.
6. Paint. After 3 hours, paint over the treated areas with a radiator enamel, then give the whole radiator a coat so the finish is even.
7. Let the paint cure before you turn the heating back on. Follow the paint tin for how long.

What about chrome towel rails?

Here we'd rather be straight with you. Rust Halt is for iron and steel, not chrome. When a chrome towel rail rusts, it's because the plating has failed and the steel underneath is exposed. You can treat those exposed spots and touch them in, but you need to mask the chrome around them carefully, and a pitted chrome rail rarely looks perfect again. If it's badly pitted all over, replacing it is often the better answer.

The same goes for aluminium radiators: they don't rust in the same way, and a rust converter isn't the right product for them.

How to stop it coming back

• Touch up chips in the enamel as soon as you see them, before rust gets a hold.
• Run the bathroom extractor fan during and after showers so the towel rail isn't sitting in condensation.
• Get weeping valves fixed early. A drip you can live with today is tomorrow's rust streak.
• If you've had pinhole leaks, ask a heating engineer about flushing the system and adding inhibitor, because the rust is coming from the inside.

Frequently asked questions

Can I use rust converter on a hot radiator?
No. Turn the heating off and let the radiator go cold first. The converter needs time to react, and heat dries it before it's done its job.

Do I need to strip the radiator back to bare metal?
No. Brush off the loose rust and flaking paint, and the rust converter deals with the rust left in the pits.

What paint should I use afterwards?
A radiator enamel, which is made to cope with the heat. Rust Halt converts the rust into a paint-ready surface, so you can paint over it after 3 hours.

Will it work on cast iron radiators?
Yes. Cast iron is iron, so Rust Halt works on it, and the gel works well into the fins and decorative detail on column radiators.