Water dripping from or under your boiler, or from a pipe outside? What to do first, the usual causes and why a leaking boiler needs a Gas Safe engineer.
By AJ, certified Gas Safe engineer and lead plumber at 247 Emergency Plumbers Edinburgh · Checked
A leaking boiler needs a Gas Safe registered engineer. First, catch the water in a bowl, keep it away from electrics and switch the boiler off at its fused spur if water is near the wiring. A drip from a copper pipe outside is often the pressure relief valve releasing water because the pressure is too high.
Smell gas, or a carbon monoxide alarm is sounding? Do not reset the boiler. Open windows, turn off the gas at the meter if it is safe to do so, leave the building and call the free gas emergency line on 0800 111 999. What to do →
What it could be and what to do
Drip from a copper pipe outside You may be able to fix this
Likely cause: The pressure relief valve releasing water because the system pressure is too high, often after a filling loop has been left open.
What to do: Check the pressure gauge and make sure the filling loop taps are fully closed. If it keeps dripping, call an engineer.
Drip under the boiler Engineer needed
Likely cause: A loose or badly fitted pipe joint, or a worn seal.
What to do: Put a bowl underneath and keep water away from electrics. A Gas Safe engineer needs to find and fix the joint or seal.
Water from inside the casing Engineer needed
Likely cause: Worn internal seals, corrosion or a failing heat exchanger. A cracked heat exchanger can mean the boiler needs replacing.
What to do: Switch the boiler off at the fused spur if water is near wiring. Never open the casing. Call a Gas Safe engineer.
Pressure keeps dropping Engineer needed
Likely cause: Water is escaping somewhere in the system, from the boiler, a radiator valve or hidden pipework.
What to do: Note how often you need to top up and look for damp patches. Repeated loss needs an engineer.
Safe checks you can do for most codes
These are the only checks we suggest without an engineer. Never remove the boiler casing.
Pressure: look at the gauge. Most boilers need about 1 to 1.5 bar when cold. If it is low, top up using the filling loop as shown in your manual.
Gas supply: check your cooker or hob works, and that a prepayment meter has credit.
Frozen condensate pipe: in freezing weather, warm the white plastic pipe outside with warm (not boiling) water or a hot-water bottle, only where you can reach it from the ground. How to thaw it safely →
One reset: press reset once, as your manual describes. If the code comes back, stop and call an engineer; repeated resets can lock the boiler out.
Controls: check the programmer, thermostat and any smart controls are calling for heat.
Code still showing? Our Gas Safe engineers can fix it.
Boiler repair labour is £90–£350 in standard hours, plus the callout from £75 (out of hours £100–£180). The price is agreed before work starts. Tell us the make, model and code when you call.
Our emergency line is open 24 hours a day, 7 days a week.
Every boiler is different. Check your boiler’s own manual. This page is general guidance, not a diagnosis.
YOUR QUESTIONS, ANSWERED
Helpful answers before you call.
Is a leaking boiler an emergency?
Treat a steady leak, or any leak near electrics, as urgent: switch the boiler off at the fused spur, catch the water and call 0131 210 0505. A slow drip from the outside relief pipe is usually less urgent.
Why is the pipe outside my boiler dripping?
Usually the pressure relief valve releasing water because the system pressure is too high. Check the gauge and that the filling loop is fully closed.
Can I fix a leaking boiler myself?
No. You can catch the water and switch the boiler off, but never open the casing. Leaks inside the boiler need a Gas Safe registered engineer.
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