Water is leaking from my boiler – what can I do?


“Why is my boiler leaking?” – if you’re asking this question, it’s likely your boiler needs attention fast – before puddles form on your floor and upholstery gets damp!

Boiler leaking water

Gas boilers leak for many reasons, so we’ll explore all the possibilities below. This will help you decide whether to dig out your toolkit or phone a professional for help.

6 reasons your boiler might be leaking water

Here are 6 of the most common reasons your boiler might be dripping water:

  1. Low boiler pressure – If this is the case, you’ll need to top up the pressure to try and correct it.
  2. Blocked pressure relief valve – This may be blocked, stopping it from closing correctly. The result is that water can leak out.
  3. Damaged heat exchange – This crucial part of the boiler heats your water. So, if it leaks when the central heating system is on it could indicate a fault or breakage.
  4. Poorly sealed joints – The pipes connecting to the boiler may be poorly sealed, damaged or come loose over time. This can cause your boiler to leak water from the connecting pipes at the bottom of the boiler. This is a common fault if you have recently installed a new boiler.
  5. Automatic air vent is leaking water – If water is leaking from the top of your boiler, there’s a good chance it’s due to an auto-air vent that’s stuck – and begins releasing water and air.
  6. Entropy! – Your boiler may be getting old, and several parts may need to be fixed (including the bits mentioned above). For example, micro-particles carried by water corrode your system over time, dissolving rubber seals and pipework until they leak.

What do I do if my boiler is leaking?

Don’t panic. Several solutions will help you to fix a leaking boiler, whether it’s a simple tweak or time to call the engineer. The solution offered below is one of the most common processes you can follow to help stop a boiler leak.

Try following these steps:

  1. Turn off the electricity – Before doing anything, it’s wise to turn off the electricity supply. You don’t want to get a nasty shock, or damage the electrical components in the boiler.
  2. What’s the pressure gauge saying? – Boilers are fitted with a pressure gauge – this is the first point of investigation. If your dial is turned up to red, there’s a good chance your pressure release valve is letting off steam (and possibly water, too).
  3. Check the filling loop, and its keys and levers – These can be stuck on ‘open’, letting water leak into the system. The filling loop is usually a silver, bendy pipe with a coloured valve or tap connecting to the boiler.boiler leaking water from relief valve
  4. Bleed radiators – If these keys/levers are not stuck open, you will need to bleed the radiators. Before you do this, you must let the system cool down so that it doesn’t spray out hot water.
  5. Switch the boiler back on and check pressure – After this, you’ll need to switch the boiler back on and watch the pressure gauge. If it goes straight back into the red, you’ve got a problem. You will need to call boiler repair services to investigate further.

How can you tell if your boiler is leaking water?

The answer’s not as obvious as you think. You may see water dripping out of your boiler (more or less dramatically), but this isn’t always the case at first.

For example, your boiler may cut out due to low pressure, or fail to heat water properly. In this situation, it loses pressure quickly, even after a top-up. Equally, your boiler display may show an error code which indicates that something is broken or faulty.

If this happens, then investigate the area around your boiler for visual clues. Warped wooden surfaces and stained wallpaper near piping may indicate a leak. You may also see small puddles forming or liquid trickle down connecting pipes.

Where is my boiler leakage coming from?

Boilers can leak from several places, indicating that other parts might be broken or faulty. Here are several common sources to check:

Boiler leaking water from the bottom – This is a typical place to find a leak…but it could happen for numerous reasons. For example:

  • A faulty heating pump
  • A blocked or broken pressure release valve,
  • A corroded heat exchanger
  • An auto-air vent fault

Condensate pipe leaking

This is often a plastic pipe leading outside of your home. If you have a condensing boiler, it allows the condensation to exit the boiler system. This can leak due to a broken heat exchanger, which allows hot water into the line – sometimes from the mains water supply – thus eroding the seals. To fix this, you’ll need to get a new heat exchanger.

Combi boiler overflow pipe leak

This is another pipe that can be found outside your house. It can leak if there’s high boiler pressure, or if the valve isn’t closed correctly. A heating engineer can check and fix this problem.

Boiler flue leaking water

This is a short exhaust pipe that leads outside your home. You might have the boiler flue installed at the incorrect angle (or installed poorly). In that case, condensation can build up inside and eventually leak water.

Boiler leaking from the top

This can be a sign of a faulty auto-air vent that needs to be fixed.

Is a boiler leaking water dangerous?

boiler leaking water when heating on

Potentially. It’s a problem that can worsen and cause several problems. Leaking water could short your electrics, damage upholstery and surfaces, or even break the internal workings of your boiler.

However, it could explode or start a fire in severe cases, so you must get it fixed as soon as possible to prevent the worst from happening.

Can you use a leaky boiler?

It’s not advisable. While your boiler may still function, continued use will only worsen the leak. If you don’t know the cause, you could be encouraging a dangerous leak to escalate or make your boiler unsafe to use.

Can you fix a leaky boiler yourself?

Modest repairs are easy enough to do, but be careful with the inner workings of your boiler. That’s best left to the experts for your own safety.

Here are two small fixes you can do yourself:

  1. Tighten the fittings on loose joints – you can often fix leaky pipe joints with a good spanner. This may be needed after a new boiler installation, where there are naturally some initial imbalances in the system.
  2. Apply boiler additives – this is a chemical solution which is added to your boiler system, which finds micro-leaks and blocks them up. Naturally, this fends off the problem for a while, but doesn’t provide a lasting solution or fix the root of the problem.

Beyond these minor fixes, and resetting the pressure, it’s best to get professional help.

Can you fix a leaky boiler yourself

Boiler error codes that indicate a water leak, and what they mean

Your boiler display will sometimes show error codes when water leakage is detected. Here are some of the codes to watch out for across the most common boiler types and brands:

On Worcester Bosch boilers

Codes you might see:

  • A1 – the air pump is jammed or dry
  • CE207 – water pressure too low
  • H07 – water pressure extremely low

Boilers where you will likely see these codes: Nearly all Worcester boilers can display these codes.

On Vaillant boilers

Codes you might see:

  • F24 – not enough water in the boiler
  • F22 – too little water pressure
  • F73 – water sensor signal in a low range
  • F13 – issue with heating flow thermistor
  • S41 – water pressure too high (above 2.8 bar)
  • S53 – insufficient flow through the boiler

Boilers where you are likely to see these codes: Vaillant boilers tend to show these codes on their ‘Eco’ models, for example, the EcoMax Pro, EcoTEC Pro & EcoTEC Plus.

BAXI boilers

Codes you might see:

  • E78 – minimum gas valve current,
  • H02-H06 – indicates a temporary fault, including a water leak,
  • 117 – water pressure too high
  • 118 – water pressure too low
  • 125 – circulation fault in the system

Boilers where you are likely to see these codes: generally on the Baxi 200 or 400 Combi boilers.

In Conclusion

If your boiler leaks water, it’s a fault you should try to correct quickly. And when the minor fixes don’t work, you should always contact a gas-safe registered engineer to examine your boiler thoroughly. Getting an annual boiler service is another way to detect these faults before they escalate.

That way, you’ll prevent further damages, and have your hot water systems up and running as soon as possible.

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