Boiler leaking water? Here's what to do
If your boiler is leaking water, switch it off and run the safe checks below first. If it still needs fixing, call 0333 772 6247 and we'll book a Gas Safe registered engineer. One-off repair visits run Monday to Friday, 09:00 to 17:00, with a £95 call-out fee. It's a service plan, not insurance.
A leaking boiler is worrying, but you're in the right place. Switch it off and isolate it at its service valves, then get a Gas Safe registered engineer to look at it, because water inside the casing sits close to live electrics. First, run three quick checks: if you can smell gas, call 0800 111 999; if water is near sockets or cables, turn the power off; and if the pressure gauge is dropping, note the reading before you do anything else.
Is a leaking boiler an emergency?
Treat a leaking boiler as urgent and turn it off straight away. It's not usually a 999 gas emergency on its own, but a slow leak can damage the unit and reach live electrics, so stop using it and get it looked at promptly. The exception is gas: if you smell gas or your carbon monoxide alarm sounds, treat that as an emergency and follow the steps below.
What should I do if I smell gas or suspect carbon monoxide?
If you can smell gas, hear hissing near the boiler or pipework, or your carbon monoxide alarm is going off, stop and treat it as an emergency. Do not touch any electrical switches. Open the doors and windows, turn the gas off at the meter control valve only if it is safe to reach, leave the property and call the National Gas Emergency Service on 0800 111 999. If anyone feels unwell, with headaches, dizziness or nausea, get into fresh air and seek urgent medical help on 999 or NHS 111. Only go back inside once you have been told it is safe.
What to do first when your boiler is leaking
- Turn the boiler off using the switch or the programmer, so it stops heating water while it is leaking.
- Catch the water in a bowl or bucket and use towels to soak up any pooling, keeping it away from sockets and cables.
- Turn off the filling loop if it has been left open, as a loop left connected can keep raising the pressure and force water out.
- If water is near any electrics, switch the power off at the consumer unit before you go near the leak.
- Isolate the water to the boiler at its service valves only if you can reach them safely and know which they are.
- Do not open the boiler casing or touch any internal or gas parts. That's always a job for a Gas Safe registered engineer.
Why is my boiler leaking water?
Most boiler leaks come down to a handful of causes: a corroded or worn internal part, a seal or joint that has failed, or too much pressure in the system pushing water out through a safety valve. Age and limescale make leaks more likely over time. Where the water is coming from is the best clue to what is wrong, so it's worth a look before you call. Left unaddressed, a leak can corrode components, trip electrics and cause damp or mould, so a small drip is cheaper to fix now than after it has spread.
Where is the boiler leaking from?
Use the guide below to work out the likely cause from where you can see the water. It's a starting point, not a repair instruction: the fix itself is for a registered engineer.
Common boiler leaks by location
| Where the water appears | Likely cause | What to do |
|---|---|---|
| From the bottom of the boiler | A failed internal seal, a corroded heat exchanger or a leaking pump | Turn the boiler off and book a registered engineer, as it's inside the casing. |
| From a pipe or valve joint nearby | A loose or worn joint, or a weeping radiator or service valve | Catch the water and book a repair; the joint can be resealed or replaced. |
| From a pipe outside an external wall (the discharge pipe) | The pressure relief valve releasing water because system pressure is too high | Have the pressure and the valve checked rather than capping the pipe. |
| Only when pressure is high, with the gauge dropping afterwards | A faulty pressure relief valve or a waterlogged expansion vessel | Note the pressure reading, then book an engineer. |
When does a leaking boiler need an engineer?
Any leak from inside the boiler casing needs a Gas Safe registered engineer, because working on a gas appliance without registration is unsafe and against the law. If the safe checks above haven't stopped a leak, call us on 0333 772 6247 and we'll arrange a one-off repair. You don't need a cover plan to book one. One-off repair visits run Monday to Friday, 09:00 to 17:00, with a £95 call-out fee covering the visit and diagnosis. Any parts and labour to fix the leak are quoted separately, and one-off repairs carry no workmanship guarantee.
If you would rather have your boiler looked after going forward, Smart Plan lets you build your own cover and pick only the modules you want. The boiler and central heating module includes parts and labour up to £500 if your boiler is under 7 years old, or up to £200 if it is 7 years or older, per 12-month period. It is monthly rolling, though once you use a service a 12-month agreement period begins, and call-outs under a plan run Monday to Friday, 08:00 to 18:00. It's a service plan, not insurance.
Still leaking? Talk to us
If the safe checks haven't stopped the leak, call 0333 772 6247 and we'll arrange a Gas Safe registered engineer. One-off repair visits run Monday to Friday, 09:00 to 17:00, with a £95 call-out fee. Or build a cover plan so the next breakdown may be covered, with call-outs Monday to Friday, 08:00 to 18:00 under your plan.
Leaking boiler: common questions
Is a leaking boiler an emergency?
Treat it as urgent rather than a 999 emergency: switch the boiler off straight away and book an engineer, because a slow leak can spread, damage the unit and reach live electrics. The exception is gas. If you smell gas or your carbon monoxide alarm sounds, call 0800 111 999, and if anyone feels unwell, with headaches, dizziness or nausea, get fresh air and seek urgent medical help.
Can I still use my boiler if it is leaking?
No, you should switch it off and stop using it until an engineer has checked it. Running a leaking boiler can worsen the damage and let water reach live electrics. Catch the water, keep it away from sockets, and book a Gas Safe registered engineer to find and fix the cause.
Why is my boiler leaking from the bottom?
A leak from the bottom of the boiler usually points to a failed internal seal, a corroded heat exchanger or a leaking pump, all of which sit inside the casing. Turn the boiler off and book a Gas Safe registered engineer, as this isn't a safe DIY fix.
Is there a call-out fee to fix a leaking boiler?
Yes. A £95 call-out fee applies to a one-off repair, covering the engineer's visit and diagnosis of the leak. Any parts and labour to put it right are quoted and charged separately. One-off repairs are not covered by a workmanship guarantee.
What hours do you carry out repairs?
One-off repair visits run Monday to Friday, 09:00 to 17:00. Call us on 0333 772 6247 during those hours and we'll arrange a Gas Safe registered engineer. If you have a Smart Plan cover plan, call-outs run Monday to Friday, 08:00 to 18:00.
Who pays to fix a leaking boiler if I am renting?
In a rented home the landlord is usually responsible for the boiler and its repairs, so report the leak to your landlord or letting agent straight away. They must keep the boiler maintained and arrange a Gas Safe registered engineer. Our gas safety guide explains the responsibilities in more detail.
What should I do if I smell gas?
Stop and treat it as an emergency. Do not touch electrical switches, open the doors and windows, turn the gas off at the meter control valve only if it is safe to reach, leave the property and call the National Gas Emergency Service on 0800 111 999. Return only when told it is safe.
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2nd Floor, Melrose House
42 Dingwall Road
Croydon
CR0 2NE