The boiler is an essential part of any modern home. Without it working you can forget about any hot showers to start the day or radiators to keep the house warm in the winter. So, if you discover your boiler’s leaking water, it’s not surprising that it can be alarming and will need urgent attention. 

It’s important to stress that any attempt to work out where the leak is coming from by opening the boiler or trying to fix it, is a job for a professional only. Boilers are extremely complex pieces of machinery that require a Gas Safe engineer to carry out any boiler repairs.

How to tell if your boiler is leaking water

If you’re reading this, it’s likely you’ve already discovered some dreaded signs that your boiler’s leaking. Perhaps there’s a small puddle of water beneath the boiler. There may be drips of water running down the wall that the boiler’s fixed to or from the boiler condensate pipe which passes through the external wall near the boiler.

Sometimes it's not obvious there's a leak at all. You might see signs of mould, damp or staining near the boiler. Warped skirting boards, countertops or any nearby woodwork can also be a tell-tale sign of moisture around the boiler. Don’t worry, we’re going to take you through the steps you need to take if you think your boiler is leaking water.

What to do if you have a boiler leaking water

If you’ve worked out that water is leaking from your boiler, you should follow these steps:

Turn off your heating

If a leak is uncontrollable and in the boiler, the first thing you’ll need to do is locate the power source for your boiler's electricity supply and turn it off. However, most leaks are from within the actual central heating system.

Lots of modern fuse boards have each circuit labelled. The fuse for your boiler is likely to be labelled as something like ‘water heater’. Push it so that it’s pointing down, which means that the power to the boiler has been isolated.

This will remove any chance of water meeting any live components or wiring and reduce the chance of short-circuiting or damage to your home’s heating system.

Switch off the water supply to your boiler

Just as you would with any sign of water leaking from pipes in your home, you’ll need to turn off the water supply. This means finding your stopcock.

The stopcock is a tap or valve, and you’ll usually find it beneath your kitchen sink. Because they’re rarely turned on or off, they can sometimes seize up, making them hard to turn. But with a bit of elbow grease (get a strong neighbour involved if you need to), it should eventually turn.

If you have a combi boiler with a direct water supply, you can simply shut it off by closing the main stop valve.

Get in touch with an engineer

It’s important to stress that any water leak must be looked at and fixed by a Gas Safe registered engineer. 

Book your boiler repair today.

What can cause your boiler to leak water?

Usually, the leaking is coming from the central heating system rather than the boiler, but the most likely causes of water leaking from the boiler are one of the following:

Weak or corroded pipes

Weak or rusting pipes are common causes of boilers leaking water, particularly leaks from the underside of the boiler or from radiator valves.

Over time, all metal water pipes become brittle and gradually degenerate, causing leaks in the pipework to enlarge over time.

If it’s just one part of the heating system which has become corroded, then you'll only really need to have that part replaced to resolve the issue. However, if multiple parts inside the boiler have corroded, it can become an expensive repair and may be more cost-effective to buy a new boiler.

Leaky seals

The leak could potentially be internal, meaning that the seals have begun to fail. This might be due to the water pressure of your boiler being too high but more likely it’s down to a simple case of wear and tear.

Leaks from the boiler are usually quite visible so if you identify this is the source, let the Gas Safe engineer know and they'll investigate when they arrive. Issues like this can be resolved quite quickly and cheaply with new seals. If the corrosion is extensive, however, again it may be time to get a new boiler.

Faulty installation

If your boiler was recently installed, the leak could just be down to poor installation. Occasionally, some joints and pipes aren’t fitted together correctly which would cause a water leak.

This is usually an easy thing to repair, in which case, you just need to get back in touch with the engineer who installed the appliance so that they can repair it under a guarantee.

High pressure

If your boiler pressure is too high, then this could result in water leaking. This is because the boiler needs to let out some of the excess pressure to function properly. Thankfully, this is a quick and easy fix that you should be able to do yourself.

You can tell if your boiler pressure is too high if the pressure gauge is anywhere above 2. The correct pressure of a boiler should be between 1 and 2 (or 15-30 psi) on the pressure gauge.

If you can see that your boiler pressure is too high, you can bleed your radiators using a radiator key which will reduce the pressure. If this doesn’t work, and the pressure is still over 3 bar, then a qualified engineer should relieve the pressure.

Have questions?

To get you answers quickly, we’ve gathered the most frequently asked questions on the internet around boilers leaking water for you here.

About the author

Ian Palmer-Smith

Ian is our go-to expert when it comes to plumbing, boilers and carbon monoxide safety. After 39 years (and counting) of working in operations – he knows quite a bit about appliance maintenance and repairs too. Even during washing machine debates (yes, they happen), his expertise is unmatched. Thankfully, Ian regularly contributes to the blog to share his wisdom – helping us all out when our appliances aren’t working quite as we expect.

Last year, Ian was recognised as a finalist in the Institution of Gas Engineers and Managers’ Gas Leadership Award – a real testament to his authority in the industry. He’s even represented Domestic & General at the House of Commons. There he informed everyone about the importance of carbon monoxide safety and awareness in the home.

Outside of work, Ian is usually occupied taking his sons to various sporting events, watching  football, rugby… and a little more sport.

Explore Ian’s wealth of knowledge on all things gas safety and appliance care now. You can check out some of his insightful articles below.

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