Boiler leaking water: what to do
First, check the water is really coming from the boiler. Then check the pressure gauge: high pressure is a common cause you can deal with yourself. Anything inside the boiler is a job for a Gas Safe engineer.
Signs of a leak
Baxi lists these signs: high boiler pressure, an error code, damp surfaces on or around the boiler, dripping underneath it, and corrosion on the pipes.
Where is the water coming from?
| Where | What it usually means | What to do |
|---|---|---|
| A copper pipe through the outside wall, dripping | That's the pressure relief valve's discharge pipe. Worcester Bosch says if it's wet, the pressure relief valve may be faulty. Very high pressure is another cause Ideal lists. | Check the pressure gauge. If it's high, bring it down by bleeding a radiator. If the pipe keeps dripping, call an engineer. |
| The white plastic condensate pipe | This pipe carries water from the boiler to a drain, so water running into the drain is normal. A leak from a joint or a crack isn't. | If it's leaking from the pipe itself, call an engineer. In freezing weather, see our frozen condensate pipe guide. |
| Radiator valves or pipe joints | Worcester Bosch says to start by checking all visible joints, including radiator valves and connections. | Put a container under it and get a plumber or heating engineer to fix it. |
| Inside or underneath the boiler casing | Ideal lists wear in the pipework, joints, seals, pump or heat exchanger. | Don't open the casing. Call a Gas Safe registered engineer. |
| Nowhere visible, but the pressure keeps dropping | Worcester Bosch says to consider leaks in pipework under the floor. | Call an engineer to trace it. |
What you can safely do
- Look carefully at where the water is coming from: the boiler itself, or nearby pipes and radiator valves.
- Check the pressure gauge. Ideal says a reading well above normal, around 2 bar or more, could be causing the leak.
- If the filling loop under the boiler has been left open, close it. Ideal says that's usually why pressure is high.
- If the pressure is high, bleed a radiator to bring it down, as Ideal and Baxi advise.
- Put a towel or container under the drip to protect the floor.
Call a Gas Safe engineer if
- The pressure is normal but the boiler is still leaking. Ideal says that points to wear in the pipework, joints, seals, pump or heat exchanger.
- The pressure keeps rising, which can mean a faulty expansion vessel.
- Water is near any electrical parts. Don't touch the inside of the boiler.
Common questions
Is a leaking boiler dangerous?
Ideal warns that gas, water and electricity are a lethal combination in the wrong hands. Don't open the boiler casing or try to repair it yourself. Get a Gas Safe registered engineer.
Why is my boiler leaking water?
Ideal lists high system pressure, a filling loop left open, a faulty expansion vessel, and wear in pipework, joints, seals, the pump or the heat exchanger.
Can high pressure make a boiler leak?
Yes. Ideal says pressure well above the normal range, around 2 bar or more, can be the cause. A filling loop left open is a common reason for high pressure.
Sources
- Ideal Heating: my boiler is leaking water, what should I do?
- Baxi: how to tell if my boiler is leaking
- Baxi: how to fix high boiler pressure
- Worcester Bosch: boiler pressure FAQ
- Worcester Bosch: the heating system is constantly losing pressure, what should I do?
Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check