Boiler leaking water — what to do right now
A leaking boiler is never something to leave. Water and electrics in the same casing means the PCB is on borrowed time, and a slow leak will rot the heat exchanger from the outside in.
Where the water is coming from tells you almost everything about the cost — so it is worth two minutes with a torch before you pick up the phone.
Try this first — free
Checks you can safely do yourself
Turn the boiler off and isolate the water
Switch the boiler off at the fused spur and close the isolation valves under the unit. Do not keep running it and hope.
Work out where the water is coming from
Under the pipework at the bottom means a joint or valve. From the casing seam means an internal component. From the condensate pipe means a blocked or split trap.
Check the pressure gauge
If pressure is also dropping, the leak is on the sealed side. If pressure is fine, you are likely looking at a mains or condensate leak instead.
Photograph it
Send us a photo on WhatsApp and we will normally tell you what it is and what it costs before we set off.
Never remove the boiler casing or touch gas components yourself — that's illegal as well as dangerous. Anything behind the front cover is Gas Safe work.
If that didn't fix it
What it usually turns out to be
Loose or corroded pipe joint
Cheapest outcome. Remake the joint and the leak is gone.
£120 – £180
Split or blocked condensate trap
Common on boilers 6+ years old, often mistaken for something serious.
£130 – £220
Pump head or auto air vent seal
Weeping seals drip onto the casing. Straightforward part swap.
£160 – £300
Failed diverter valve cartridge
Often leaks and gives you lukewarm hot water at the same time.
£220 – £380
Corroded heat exchanger
Terminal on most boilers. Cost of the part plus labour rarely makes sense past 8 years.
£500+ or replace
Prices inc VAT and include our £99 diagnostic. We confirm the price before any work starts — no surprises on the invoice.
Straight talk
When we'd tell you to replace instead
- Water has been sitting on the PCB or wiring loom
- The leak is from the main heat exchanger casting
- The boiler is 10+ years old and this is not the first leak
- The model is obsolete and the part has to be sourced second-hand
Active leak plus electrics is a same-day priority job. Call us and we will get you on today's list.
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Frequently asked questions
Is a leaking boiler dangerous?
Water alone is not a gas risk, but water reaching the electrics can be. If it is dripping onto the PCB, turn it off at the spur and get an engineer out.
Can I use my boiler if it is leaking?
Only briefly, and only if the leak is external pipework rather than the boiler itself. A leak from inside the case should be shut down.
Will my insurance cover it?
Home emergency cover usually does. Standard buildings insurance usually covers water damage but not the boiler repair itself.
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