What is causing a leaking boiler?

Published on December 8, 2021

Gas Safe Plumber

Boiler repair: what’s causing a leaking boiler?

If you’re reading this then your boiler is probably leaking (or you suspect it is), and no doubt you’re worried about the prospect of living without heating and hot water while it’s being repaired. In this blog, we look at what might be causing your leaking boiler, how to deal with it, and the steps you can take to prevent it happening again.

How do I know if my boiler is leaking?

The most obvious sign that your boiler is leaking is a puddle of water underneath it. In this case, it’s clear that something is wrong, but there might be other reasons you suspect there is a problem with your boiler:

  • a sudden change in boiler pressure
  • stains, mould, or damp on the walls or ceiling near your boiler
  • signs of corrosion on the pipes or outer casing

If you have a modern boiler, it might also have a display panel that shows an error code when something is wrong – take a look in your manual for help decoding it.

Though you’ll be keen to get to the bottom of the problem quickly, you should never attempt to remove the outer casing of the boiler yourself. Leave it to the professionals, who are trained in finding their way around a boiler safely and efficiently.

What’s causing my leaking boiler?

There are several reasons your boiler might be leaking, and we’ll cover the most common here.

Boiler pressure

The pressure in your boiler should be between 1 and 2 (or within the ‘green range’). You can check this on the gauge on the front of your boiler. If the pressure is too high then the pressure release valve (PRV) will start to drain off the excess water. It is possible to reset the pressure yourself by ‘bleeding’ your radiators to release the build-up of air.

Badly fitted pipework

It’s often the case with a leaking combi boiler that a pipe hasn’t been fitted correctly. If your boiler was installed recently then this is the most likely cause. Most reputable engineers will happily come back to tighten up any loose fitting pipework and rectify the problem.


Corroded pipework and general system wear and tear are to be expected in old boilers. If your boiler is over ten years old and has started leaking water then it’s probably time to replace it. Corrosion of a single part is possible to repair, but anything more and you will probably need to replace the whole boiler.

Faulty and broken seals

A faulty or broken seal is often the cause of a leaking boiler, particularly in older systems which have suffered decay over time. Just like corroded pipework, if the problem is isolated to one part then it may be easy to replace. If the problem is more widespread, it could be a sign that it’s time your boiler was replaced.

Faulty heat exchanger

In less expensive boilers the heat exchanger is prone to fail, which can cause a leak. It’s an essential part of the system and without it your boiler won’t be able to transfer heat generated from burning gas to heat cold water. In the majority of cases, replacing the heat exchanger wouldn’t make financial sense – the part alone is expensive and can only be fitted by a Gas Safe engineer.

What to do if you suspect a leak

A leaking boiler isn’t dangerous but it does need looking at as a priority to prevent any further damage – corrosion, rust, or an electrical malfunction are all possible.

If you can see water leaking from your system, then try to contain it as much as possible. This might be as simple as using a bowl to catch the dripping water, but if this is not enough you may need to turn off the water supply and switch off your heating.

Unless it’s as obvious as bleeding your radiators, then the problems we’ve covered above all need a Gas Safe engineer. Never attempt to fix a boiler leak yourself, it could put you, your family ,and anyone else in your property and nearby at risk. Once you’ve contained the leak, call an engineer to look at the problem and sit back while the experts do their job.

How to prevent a leaking boiler

The best way to prevent a leaking boiler is to have it regularly checked for faults. An annual service can identify minor issues before they become bigger problems.

Maintaining your boiler is much more cost effective than paying for it to be repaired when something goes wrong. At RJ Martindale we know that servicing your boiler annually will extend its life and cut down on the cost of repair bills if it does ever need fixing. That’s why we include an annual service as standard in all our Home Care Plans.

There are four levels of cover to choose from – annual, essential, premium, and advanced, for complete peace of mind should anything go wrong, including a leaking boiler.

Cover starts from just £6.50 a month for our annual care plan, which includes a yearly service and carbon monoxide test. This plan gives our customers an affordable way to spread the cost of an annual service (£78) over 12 months.

Why choose RJ Martindale?

We are a family company in Bolton with a reputation for customer care and outstanding service, which is why we have over 180 five star reviews on Google.

We recognise that our customers don’t just want an engineer experienced in boiler repair and replacement, they want someone who is going to look after their home. We make it a priority to be cleaner, neater, and more efficient than anyone else.

As the summer months turn to autumn, you’ll start to notice a return to frosty mornings and cold nights, and if you haven’t fixed your leaking boiler, then you might find it doesn’t work when you come to use it. Don’t put off getting it fixed – contact our friendly team today and we will diagnose the problem and help you get back up and running quickly.

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