What to do if your boiler is leaking water

28 September 2023 | Celia Topping

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A leaking boiler could be a sign of a serious problem – so it’s best to act quickly.

Don’t try to fix anything inside your boiler yourself. Even if you can see where the leak is coming from, you should call in a professional heating engineer.

And that’s where we can help. If you don’t have boiler cover, we can set you up with our most comprehensive plan and repair your existing leak. With Home Recover, you’ll get the repair for free if you’re an OVO customer, or £79 if you get your energy elsewhere¹.

How to find out if your boiler is leaking water

Modern boilers use a pressurised system that’s sealed, so water can’t escape. But even if you don’t see any leaking, you might notice a loss in pressure that makes your boiler cut out. If you top it up and it loses pressure again quickly, it’s likely you have a leak.

Is a leaking boiler dangerous?

Boiler leaks can be minor, or they can be a sign of something more serious. Without knowing the cause of the leak, it can be hard to tell if it’s dangerous. But either way, your boiler will need immediate attention.

Your boiler contains electrical parts, gas, and hot water. So again, don’t open it up yourself. The best thing to do is switch it off and call a heating engineer to come and take a look.

Why your boiler is leaking water

1. Badly installed or damaged joints

One of the main causes is an issue with the pipework underneath. You can check this by feeling for any wetness around the pipes, as small leaks might not always be obvious.

Small pipe leaks are surprisingly common in newer boilers, and can be tricky to spot when they’re first installed. Leaks can happen from expansion and contraction that make mechanical fittings loose over time – or they can occur from accidental damage (like banging the hoover against a radiator pipe).

In older boilers, most water leaks come from pipe joints. These can be easily repaired with replacements which a professional should fit for you.

If it doesn’t look like the leak is coming from the joints, your pipes might have corroded. You could get a short-term repair. But if it’s out of warranty, it’s probably best to replace your boiler sooner rather than later, or ask a heating engineer to take a look.

It’s recommended to review what you can resolve yourself (such as tightening up compression fittings at the radiator) – but working on your gas appliance will require a qualified engineer.

We know this can be expensive. So we’ve written a helpful guide that explains the different types of boilers, and how to choose the right one for your home.

2. Too much pressure

For most boilers, the needle on the pressure gauge should stay between 1 and 2 bar.

If the needle is way over 2, then the boiler pressure is too high. This means there’s too much water in the boiler, and the pressure release valve (PRV) will let some of the excess out. This will be the leak.

Pressure gauge diagram showing when pressure is too low or too high

How to fix high boiler pressure

It’s usually fixed by bleeding the radiators. But first, check if the filling loop tap is firmly closed (so the handle is across the body of the valve). This is the silver, flexible pipe under your boiler – with 1 or 2 taps.

Then, you can watch OVO heating engineer Rich Laniyan talk you through how to bleed your radiators.

3. Corrosion and general wear and tear

Boilers don’t last forever. The mix of water and bits of metal in the system can eventually wear the pipes and cylinders, so they become fragile and break. This is called corrosion.

Some parts can be replaced easily, but over time, this wear and tear might mean you need a new boiler.

4. Faulty heat exchanger

The heat exchanger is one of the most important parts of your boiler. It’s common for them to fail in old boilers, and even in newer ones.

If the heat exchanger is the problem, you’ll need to call out a qualified engineer. It can be expensive to repair or replace, so it’s probably a good time to think about getting a new boiler.

5. Leaks from seals on internal parts

Water always runs through your boiler, so the seals on the joints inside can sometimes rot. High pressure can also cause joints to leak.

Fixing a basic boiler leak yourself

Boilers can be really dangerous if you don’t have the right experience. So in most cases, it’s best to call an expert.

But you could attempt to repair a very basic boiler leak – as long as you’re feeling confident. If you can see dripping from a joint on one of the pipes underneath your boiler, dry the area and double-check that’s where the leak is coming from. If it is, then tighten the fitting and see if it helps.

Sealants might also help repair a smaller leak, although they can be tricky to apply. Plus, they’re not really a long-term solution. So it’s probably best to call a Gas Safe engineer to come and fix it.

How to avoid a boiler leak

Getting regular boiler check-ups is the best way to prevent problems. With our boiler cover plans, you get a yearly service. Plus access to Gas Safe engineers, unlimited callouts, and a 24/7 emergency helpline. All you have to do is pick the plan that works for you1.

What to do if your boiler is leaking oil

This is only relevant if you use heating oil in your boiler. If the smell of oil is stronger than usual, or if you spot stains or pools of oil, you could have a leak.

Close the tap or valve on the oil tank straight away, and open the windows to clear any fumes. Put a bucket under the leak to catch the oil, but don’t wash the oil away. Call out a heating engineer straight away. If anyone feels sick or dizzy, get out of the house as soon as you can.

Get boiler, plumbing, heating, or electrics repair with Home Recover

At OVO, we want to be there for you in an emergency – whether you’ve got cover or not.

If something goes wrong with your boiler, plumbing, or electrics, we’ve got you. With Home Recover, we’ll fix it for free for OVO customers (or £79 if you get your energy elsewhere) when you take out our Complete cover plan1.

Our experienced, independent network of engineers is already trusted by over 200,000 UK homes2. And with our 24/7 emergency helpline, we’ll help you get up and running again as soon as possible.

Sources and references:

¹ Exclusions, eligibility criteria, cancellation fees, and terms and conditions apply.

² OVO Energy and CORGI HomePlan are part of the OVO family, and as a group serviced 215,927 boilers in 2022.