Should I turn my boiler off if it's leaking?

Yes. Turn it off and isolate the water supply to it if you can, to limit damage, then book a Gas Safe engineer.

Why is water coming out of the pipe outside?

That outside pipe is usually the pressure-relief discharge. Water from it often means system pressure is too high or a valve has failed — an engineer can bleed and re-pressurise it properly. Don't keep topping the pressure up.

Common plumbing problems

Boiler leaking water: what to do and who to call

Guidance built with working UK plumbers · Last updated July 2026

A boiler leaking water should be repaired by a Gas Safe registered engineer — it isn't a DIY fix. The usual causes are system pressure that's too high (pushing water out through the overflow pipe), a corroded or failed internal part, or leaking pipework and fittings around the boiler. You can safely make it safe and do a couple of checks, but the repair is a professional job.

Smell gas? Stop. Leave the property, don't touch any switches, and call the National Gas Emergency line on 0800 111 999. Never open the boiler casing or work on its internal parts — that's Gas Safe only, by law.

Usually amber — make it safe, then get an engineer. The water is mainly a damage risk; the fix waits for a professional. Escalate to red if you smell gas or see scorching.

Do this now (homeowner-safe only)

Rule out gas. Any gas smell → 0800 111 999, leave, no switches.
Turn the boiler off and, if you can, isolate the water supply to it to limit water damage.
Note the details — where it's leaking from and the pressure-gauge reading. This speeds up the engineer's diagnosis.
High pressure? If the gauge is high (often above ~1.5 bar / in the red) and water is coming from the outside overflow pipe, don't keep re-pressurising — an engineer will bleed and reset it.
Book a Gas Safe registered engineer. Don't open the boiler.

Likely causes

Clue	Likely cause
Water from the outside overflow pipe	Pressure too high / pressure-relief valve
Leak from pipes just below the boiler	Loose or failed pipe fittings
Persistent internal leak, dropping pressure	Corroded heat exchanger or internal seal
Boiler keeps losing pressure	Leak somewhere on the sealed system

When to call a professional

Always — the repair itself is a Gas Safe registered engineer's job. Call immediately if you smell gas or see scorch marks. LeakScan helps you understand what's happening and make it safe; it is never a substitute for a Gas Safe engineer.

Questions, answered straight

Can I fix a leaking boiler myself?

No — work inside a boiler must be done by a Gas Safe registered engineer. You can turn it off, isolate the water and note the symptoms, but not repair it.

Is a leaking boiler dangerous?

The water is mainly a damage risk, but it can affect internal electrics. Any gas smell or scorching is an emergency — leave and call 0800 111 999.

Should I turn my boiler off?

Yes — turn it off and isolate its water supply if you can, then book an engineer.

Why is water coming from the pipe outside?

That's usually the pressure-relief discharge — often high pressure or a failed valve. An engineer will correct it; don't keep topping up the pressure.

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