Boiler leaking water — what to do right now
A leaking boiler is never normal. Depending on where it's dripping from it can be a £90 pressure fix or a £600 heat-exchanger job — but leaving it wet will damage the PCB and turn a small repair into a full replacement.
Make it safe — before anything else
Only Gas Safe registered engineers work on gas
It is illegal (and dangerous) for anyone who isn't Gas Safe registered to work on a domestic gas boiler in the UK. Every KJ Plumbers engineer sent to a boiler job is Gas Safe registered — ask for the card on arrival.
Isolate electric first
Water and 230 V don't mix. Turn the boiler off at its fused spur or the consumer unit before touching it. Do not unplug a boiler that is already wet.
Don't chase the leak with towels alone
Catch what you can, but the priority is stopping the water at the stopcock and the heating circuit — otherwise the drip keeps refilling itself.
What Kevin (our AI) will check first
Message Kevin and he'll ask exactly these questions before we send an engineer, so we bring the right parts on the first van.
- Where exactly is it dripping from — bottom of the boiler, pipe joint, or the pressure-relief pipe outside?
- Boiler make, model and rough age (photo of the front badge is perfect).
- Current pressure gauge reading.
- Is the pressure-release copper pipe on the outside wall dripping?
- Any recent work — new radiator, power flush, filling loop left open?
Common causes of a boiler leaking
Over-pressurised system
Filling loop left open pushes pressure past 3 bar; the PRV dumps water outside and sometimes internally. Fix: drain a little water off, close the loop, replace PRV if it now weeps.
Failed pump seal or auto-air-vent
Small drip from the top of the boiler where the pump or AAV sits. Common on boilers 6-10 years old. Replacement part typically £120 – £220 fitted.
Corroded heat exchanger
Weeping from the main body under the burner is bad news — heat exchangers on most combis cost £450 – £700 fitted and often trigger the 'replace vs repair' conversation.
Leaking pipe joint or diverter valve
Compression joint or diverter-valve O-ring perishes and drips. Straightforward fix once the boiler is drained down.
Honest cost band — why we won't quote blind
Typical
£90 – £180 for a re-pressurise, PRV replacement or simple joint fix
Complex
Pump, AAV or diverter-valve seal £180 – £340. Heat-exchanger replacement £450 – £700+.
£50 diagnostic covers a full Gas Safe check with pressure and combustion readings, and a fixed written price before any work goes ahead.
Fixed £50 diagnostic
Flat fee. No hourly meter running.
Fair quote or refund
Transparent pricing — refunded if we don't fix it.
Vetted UK engineers
DBS-checked, insured, real reviews.
AI-triaged in seconds
KJ chats first so the right engineer arrives.
Related emergencies
Boiler losing pressure
Emergency guide
Boiler on but no heating
Emergency guide
No hot water
Emergency guide
See all in the emergency plumbing hub — or the leaks & water damage hub.
Areas we cover for boiler leaking
Same-day across Greater Manchester and Rochdale.
Boiler leaking — FAQs
Dealing with a boiler leaking? Chat with Kevin now
Real triage in seconds. £50 diagnostic visit — refunded if we don't fix it.
Related hubs: emergency plumbing, leaks & water damage, all services.
Chat with Kevin about Boiler leaking