Struggling with leaks and damp spots? Check out our guide on how to fix a pinhole leak in a radiator. With step-by-step instructions, tips and prices.

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A damp patch under the radiator, or a drip you can't quite trace, is usually the first sign of a radiator leak.

Left alone, it can damage flooring, cause rust to spread, and leave your heating system losing pressure.

The good news is that most radiator leaks - including pinhole leaks - can be diagnosed and often temporarily fixed yourself, though it's worth knowing when a proper repair or replacement is the safer call.

What causes a pinhole leak in a radiator?

Pinhole leaks form when rust and corrosion eat through the radiator's metal from the inside out.

This is usually driven by sludge - a build-up of rust particles and debris that settles inside an unmaintained central heating system over time.

If the bottom of your radiator feels noticeably cooler than the top, that's often a sign of sludge build-up, which is worth addressing alongside any leak repair.

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Radiators failing to heat properly, leaking, or making unusual noises could mean it's time for repair. Find radiator repair services with Checkatrade to get this essential part of your central heating system running smoothly again.

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Can you fix a radiator leak yourself?

In most cases, yes. Small pinhole leaks, valve leaks and bleed valve leaks are all realistic DIY jobs.

However, if the radiator is heavily corroded, has a hole larger than pinhole-size, or keeps leaking after a repair, replacement is usually the more sensible option rather than repeated patching.

How to fix a pinhole leak in a radiator

Find the leak

This isn't always obvious - check the floor beneath the radiator for damp patches, or dry the radiator fully and watch for where moisture reappears.

Turn off the water supply

Plus, you'll need to drain the radiator.

Clean and dry the area around the leak

Thoroughly - epoxy putty won't bond properly to a wet or dusty surface.

Apply epoxy putty

Directly over the pinhole and smooth it into place.

Let it cure fully before refilling the radiator and switching the water supply back on.

An alternative (or additional) option is a leak sealer added to your central heating system, which circulates through the pipework and radiators to seal small leaks from the inside.

Important: Leak sealer works like a temporary plaster rather than a permanent fix, and it's only suitable for minor leaks. If you're topping up your boiler pressure regularly, or the leak returns, that points to a bigger problem that sealer alone won't solve - it's time to call a plumber.

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How to fix a leaking radiator valve

Valve leaks are just as common as leaks in the radiator body itself, and the fix is usually straightforward:

1. Turn off the water supply and drain the radiator

2. Unscrew the union nut with a spanner

3. Open the bleed valve over a bucket to let any remaining water drain

4. Wrap PTFE tape around the valve tail - around ten wraps is typical

5. Retighten the union nut with the spanner

6. Open the bleed valve, then turn the water supply back on and refill

7. Check for leaks before closing the bleed valve again

How much does it cost to repair a leaking water pipe?

A leaking pipe can cost £220–£440 to repair, or less if you catch it early. Find out what affects the price, when to DIY, and how to get a quote from a local plumber.

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Radiator leaking from the top

A leak from the top of a radiator is almost always down to the bleed valve rather than the radiator body itself:

1. Confirm the bleed valve is the source

2. Push a cotton bud gently into the bleed valve opening - if it comes away wet, you've found the leak

3. Turn the bleed key clockwise to tighten the valve screw

4. This should stop the leak; if it doesn't, the valve itself may need replacing

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How to fix a leaking bathroom or towel radiator

Towel radiators leak in largely the same places as standard radiators, so isolate the source first:

• Valves - follow the valve leak steps above

• Spindles - tighten the gland nut with a spanner, or wrap tape around the spindle

• Pipe joints - tighten the joint or wrap it with PTFE tape

• The radiator itself - follow the pinhole leak steps above

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When a hole is too big to repair

Small pinhole leaks can be temporarily sealed with epoxy putty or leak sealer, but medium and large holes generally can't be.

If your radiator is significantly corroded, or the hole is beyond pinhole-size, replacement is the realistic option rather than a repeated series of temporary fixes.

If your radiator needs replacing rather than repairing, a plumber can advise on the best size and type for the room, and handle removal of the old unit safely.

Filling holes around radiator pipes

If you've disturbed the wall around your radiator pipes during a repair or replacement, gaps left behind are worth sealing to stop draughts and keep pests out:

• Small holes: use standard filler, then sand flat and paint over once dry

• Medium holes: steel wool packed in and sealed with caulk works well

• Larger holes: a lath screen, metal sheeting, or cement gives a more permanent fix

When to call a professional

DIY pinhole and valve repairs are a reasonable first step, but if the leak keeps coming back, your radiator is badly corroded, or you're regularly repressurising your boiler to compensate, it's worth bringing in a plumber rather than continuing to patch the same fault.

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Checklist before you start

Radiator leak checklist

Before you fix a radiator leak....

• Dry the radiator to locate the leak

• Turn off the water supply

• Have towels and a bucket ready

• Clean and dry the area fully

• Check whether it's a valve, bleed valve or body leak

• Note if the leak keeps returning

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