Boiler Leaking Water? Common Causes and What to Do

A boiler leaking water should never be ignored. Water and electricity are a dangerous combination, and even a small leak can corrode components, damage your home, and lead to a complete breakdown if left unchecked. This guide explains the most common reasons a boiler leaks water and exactly what you should do.

What to do first if your boiler is leaking

If you can see water leaking from your boiler, take these steps before anything else:

Turn the boiler off at the mains and switch off the central heating.
Turn off the water supply to the boiler using the internal stop tap if the leak is significant.
Mop up standing water and place a container under the leak to protect your flooring.
Do not try to open up the boiler. The inside of a boiler should only ever be worked on by a Gas Safe registered engineer.

Common causes of a boiler leaking water

High boiler pressure: if the pressure is too high, the pressure relief valve opens to let water out, often through a pipe outside. Check the gauge — if it’s in the red, see our guide on boiler pressure that’s too high.
A faulty pressure relief valve: the valve itself can wear out and let water escape even at normal pressure.
Corroded pipes or heat exchanger: over time, internal parts corrode. A leaking heat exchanger is a serious fault and usually means a repair or replacement by an engineer.
Worn pump seals: the seals around the circulating pump degrade with age and can drip.
Loose joints and connections: pipe fittings can loosen over time, particularly after recent work on the system.

Where is the water coming from?

The location of the leak is a useful clue. Water dripping from a pipe outside the property usually points to high pressure or a faulty pressure relief valve. Water pooling underneath the boiler often indicates a failed seal, corroded pipe, or heat exchanger fault. Either way, the internal cause needs a professional diagnosis.

Is a leaking boiler dangerous?

A leaking boiler isn’t usually an immediate danger, but it shouldn’t be left. Water can reach electrical components and cause a short, corrosion accelerates once it starts, and a leak can quickly turn a small repair into a full breakdown. If you ever smell gas as well as seeing a leak, turn off the gas at the meter and call the National Gas Emergency line on 0800 111 999 immediately.

When to call a professional

Almost all boiler leaks need a Gas Safe registered engineer. The one exception is high pressure, which you can often reduce yourself by bleeding a radiator — but if the pressure keeps climbing or water keeps leaking, the underlying fault still needs fixing. Never attempt internal boiler repairs yourself.

Frequently asked questions

Can I still use my boiler if it’s leaking?

No. Turn it off and avoid using it until an engineer has inspected it. Running a leaking boiler risks electrical faults and further damage.

Why is my boiler leaking water from underneath?

A leak underneath usually points to a failed internal seal, a corroded pipe, or a heat exchanger fault — all of which need a Gas Safe engineer.

Why is water coming from the pipe outside my house?

That’s the pressure relief valve discharge pipe. It releases water when boiler pressure is too high or the valve is faulty. Check the pressure gauge first.

Need a boiler engineer in West London?

If your boiler is leaking, don’t wait for it to become a full breakdown. Our Gas Safe registered engineers provide fast, reliable boiler repairs and plumbing and heating services across West London, often fixing the problem in a single visit.

Tel: 020 3561 4415