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Boiler leaking water? What to do straight away
Turn the boiler off, contain the water and keep it away from the electrics. Then work out where it’s coming from: a drip from a pipe outside is very different from water inside the casing.
- 1copper pipe outside to check first
- 0times you should take the casing off
- £120repair visit, including VAT
!act straight away
Water around your boiler is something to deal with straight away. Even a small leak can wear parts out and damage the kitchen, and water near the electrics is a real risk.
The good news is that not every drip means the boiler’s failing. Here’s what to do first, and how to tell what kind of leak you’ve got.
What to do right now
Before you work out the cause.
Turn the boiler off
Switch the heating off at the boiler. If water is near the electrics, switch it off at the spur on the wall too, but only if the spur is dry and you’re not standing in water. If it’s wet, or water is coming through a ceiling near lights, switch off at the fuse box and don’t use those lights.
Contain the water
Put a bowl or towels under a small leak and keep an eye on it. If it’s a big leak or water’s coming through a ceiling, turn the water off at the stopcock.
Leave the casing on
Don’t take the cover off to look. Only a Gas Safe registered engineer should open a boiler.
Call an engineer
Worcester’s advice is the same as ours: turn the boiler off and contact a Gas Safe registered engineer.
Know where your stopcock is
The ABI advises knowing where your stopcock is and testing that it works. It’s usually under the kitchen sink.
Where leaks come from
Where the water is tells you a lot.
A copper pipe dripping outside
That’s usually the pressure relief valve’s discharge pipe. The valve lets water out when the pressure gets too high, often from overfilling, a filling loop left open or a failed expansion vessel, or the valve itself can be faulty. Check the gauge.
Water at the bottom of the boiler in a frost
A frozen condensate pipe can back up and push water out at the boiler. Thaw the pipe outside.
Water from inside the casing
That’s a failed seal, the pump, or a corroded or cracked heat exchanger. It’s a job for an engineer, and it often makes the pressure drop too.
Joints and valves on the pipework
Pipework, joints and radiator valves can weep over time. Worcester also says to think about pipes under the floor if pressure keeps dropping.
Finding the leak
Leaks and pressure
They usually go together.
If your boiler’s pressure gauge drops suddenly, water is probably escaping somewhere. Having to top up the pressure more often than normal is an early warning sign, even if you can’t see a leak.
It works the other way too. Pressure that’s too high makes the relief valve open and drip outside.
- Gauge keeps dropping: look for a leak
- Gauge above about 2.5 bar: with the heating off and cold, bleed a radiator until it’s back to 1 to 1.5 bar
- Dripping outside: check the pressure, then book a repair
Pressure check
What should I do next?
- Water near the electricsSwitch off safely
At the fuse box if the spur is wet. Then call us.
- Copper pipe dripping outsideCheck the pressure
Too high opens the valve.
- Water in a frost, gurglingThaw the pipe
Condensate backing up.
- Leak from the boiler itselfBook a repair visit
£120 including VAT, before any parts.
Common questions
Is a leaking boiler dangerous?
It can be. Water can make electrical parts fail and, in the worst case, catch fire. Turn the boiler off, keep water away from the electrics, and call a Gas Safe registered engineer.
Should I turn my boiler off if it’s leaking?
Yes. Turn it off at the boiler. If water is near the electrics, switch off at the spur if it’s dry, or at the fuse box if it isn’t. If it’s a big leak, turn the water off at the stopcock too.
Why is water dripping from a pipe outside my house?
If it’s a copper pipe from the boiler, it’s most likely the pressure relief valve letting water out because the pressure is too high. If you have a hot water cylinder, it could be its safety valve instead. See our unvented cylinder guide.
Can I fix a boiler leak myself?
Not inside the boiler. You can bring high pressure down by bleeding a radiator and thaw a frozen condensate pipe. Anything inside the casing is for a Gas Safe registered engineer.
Why does my boiler keep losing pressure but there’s no leak?
The water may be escaping somewhere you can’t see: the relief valve pipe outside, a radiator valve, or pipework under the floor. A failed expansion vessel can also make the relief valve open.
Is a boiler leak covered by Home Care?
Breakdown repairs to the boiler are covered on the Boiler and Complete plans. Radiators and valves are covered on Complete. Faults that were there before you joined, and damage caused by sludge or scale, aren’t covered.
Related pages
Sources: Worcester Bosch, boiler leaking water; Vaillant, why is my boiler leaking water?; Ideal, my boiler is leaking; Worcester Bosch, losing pressure; ABI, cold weather advice. Checked 2 November 2026.
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