Why Is My Boiler Leaking Water?

Your boiler is leaking water. Here are some quick checks you can do:

DIY Checks You Can Do

Turn off the boiler
Switch it off immediately to prevent further damage.

Check where it's leaking
Is water coming from the bottom, pipes, or pressure relief valve? The location helps identify the problem.

Check boiler pressure
If the pressure gauge shows above 2.5–3 bar, the pressure is too high.

Look for obvious damage
Check for corroded pipes, loose connections, or damaged seals around the boiler.

Put towels down
Protect your floor and catch dripping water.

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Common Causes of Boiler Leaks

Common Causes of Boiler Leaks

Pressure Too High
If system pressure is too high (above 2.5 bar), the pressure relief valve releases water to prevent damage. This is a safety feature.

What to check: Look at the pressure gauge. Normal is 1–1.5 bar when cold.
What causes it: Overfilling when repressurising, or a faulty expansion vessel.
What to do: If pressure is high, you may need to bleed a radiator to reduce it. If it keeps rising, call an engineer.

Pressure Relief Valve Faulty
Signs: Water dripping from the copper pipe outside.
Causes: Valve stuck open or debris.
Fix: Valve needs replacing by an engineer.

Pump Seal Failure
Signs: Water leaking from the pump area.
Causes: Age, wear, or pump running dry.
Fix: Seal or pump replacement needed.

Corroded Pipes or Heat Exchanger
Signs: Drips or puddles under boiler, rust stains.
Causes: Age, sludge in system, or aggressive water chemistry.
Fix: Depending on severity, repair or boiler replacement.

Loose Connections
Signs: Water at pipe joints or fittings.
Fix: Often just needs tightening, but may need new washers or seals.

Is a Leaking Boiler Dangerous?

Water leaks themselves aren’t usually immediately dangerous, but:

Electrical risk – Water and electrics don’t mix. Turn the boiler off at the fuse box if water is near electrical components.
Property damage – Ongoing leaks damage floors, ceilings, and belongings.
Boiler damage – Running a leaking boiler can cause additional damage and more expensive repairs.
Low pressure problems – Leaks cause pressure loss, so the boiler won’t fire properly.

What to Do About a Leaking Boiler

Turn it off – Switch off at boiler controls and fuse box if needed.
Isolate water supply – If the leak is severe, turn off water at the filling loop or mains stopcock.
Catch water – Use towels, buckets, or trays to protect property.
Take photos – Useful for engineers and insurance if needed.
Don’t use it – Don’t turn the boiler back on until repaired.
Call an engineer – Get professional diagnosis and repair.

Can I Fix a Leaking Boiler Myself?

Generally no. Boiler repairs require a Gas Safe registered engineer. Even if it seems like just a loose connection, boilers are complex and working incorrectly can be dangerous.

The only DIY action: If pressure is too high, you can bleed a radiator to reduce it.

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