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General Boiler info, Troubleshooting

How to diagnose a leaking boiler

Why is my boiler leaking?

If you’ve found water leaking from your boiler, the important thing is not to panic. We’ll help you diagnose the issue, and then show you what needs to be done. We have plenty of advice on boilers: how long they last, when they need replacing, and what you can do to make them last longer.

Diagnosing a leaking boiler

First you need to assess your boiler’s current status. Here’s a list of reasons why there might be a standard or combi boiler leaking problem.

How old is it?

Boilers should last around 10 – 15 years. They need to be serviced every year, and you should look after it properly.

Boilers lose efficiency over time. A 15-year-old boiler will be less efficient than a brand new one. This might mean your energy bills will be higher with an older boiler: up to £315 a year higher, according to the Energy Savings Trust.

When will it need replacing?

There are a few signs to watch out for that your boiler might need replacing. Here are some common ones:

  • Your boiler frequently breaks down or needs repairs
  • It takes a long time for radiators to warm up
  • Low or high hot water pressure
  • Hot water isn’t hot enough
  • The boiler makes strange noises
  • It keeps losing pressure
  • Your heating bills are unexpectedly higher

If any of these are happening in your household, it could be a sign that your boiler's getting on a bit and might need replacing soon.

Check your boiler

If you’ve noticed your standard or combi boiler leaking, the first steps to take are to examine the boiler itself, and all surrounding pipework. If you’re asking ‘why is my boiler leaking?’ You should check for the following:

  • High boiler pressure
  • An error code on your boiler
  • Damp surfaces on or around the boiler
  • Dripping beneath it
  • Corrosion on the pipes

If you’ve taken a good look, and any of these issues are present, then there are steps you can take to help fix a leaking boiler.

How to fix a leaking boiler - Boiler pressure too high

Good boiler pressure needs to be between the 1 and 1.5 bar on the pressure gauge. That’s the happy zone for boilers.

If it’s higher than this, it’s usually due to setting the boiler pressure too high when topping up. The filling loop might not be closed tight enough, which lets more water in. Whatever the reason, when your boiler pressure’s high, the pressure release valve opens and lets some of that pressure escape.

If this is what is happening, you might notice dripping water and residue build-up from the copper pipe leading from your boiler to outside. If it happens a lot, there may be a problem.

It could be the build-up of sludge inside the pipe stopping the pressure release valve from closing properly. This might answer ‘why is my boiler leaking?’ It’s something that’s easily cleaned when the heating engineer services the boiler.

Another way to reduce high boiler pressure is to bleed your radiators. You probably need a radiator key to do this, but some radiators can be bled with a screwdriver. Make sure your central heating is off, and the radiators are cool! The water inside can be hot enough to scald, so always be safe! Read our guide to bleeding radiators for more info.

Error codes

Modern Baxi boilers have a whole range of error codes that will help diagnose the issue ‘why is my boiler leaking?’ An example error code you may see if there’s water leaking from your Baxi boiler is E119. This means there’s a fault with the system water boiler pressure, or water is leaking. You can find the whole list of error codes here, along with more info about what to do about them.

Water leaking from boiler pipes or joints

Take a good look at the pipes going in and out of your boiler, particularly around any joints or fittings. If there’s wetness anywhere, gently dab it dry. Wait a short while, and check to see if it’s wet again.

If it is, you might need to tighten any connectors near the source of the leak. You’ll need a spanner for this. Simply tighten the connector no more than a quarter-turn: over-tightening can damage pipes, particularly older ones. Alternatively, contact a heating engineer to do this for you.

Corrosion in pipes and seals

If tightening the connectors didn’t work, it may be because the seals inside the leaking combi boiler joints are worn, corroded, or have come loose. If that’s the case, you WILL need a heating engineer to take a look and sort this out for you.

Corrosion mostly happens in older boiler systems. Hard water areas are more prone to corrosion, too. It’s a problem because it nearly always happens inside the pipes for a long time before you notice it on the outside. If your leaking boiler and piping is particularly old, we recommend you ask a heating engineer to check if the pipes are corroded.

Can I still use my boiler if it’s leaking?

While a leaking boiler is not usually as dangerous, it’s still a problem that needs fixing. Like most problems, it doesn’t just go away, and will only get worse the longer you leave it.

If you’re asking ‘why is my boiler leaking?’, the best advice is to run through our handy checklists above, and then see if there’s any way you can stop water leaking from your boiler. If you’ve tried everything, it’s time to bring in a heating engineer. Most boiler leaks can be fixed with a home visit. Even if the engineer can’t repair it, they’ll at least give you advice on whether you need to replace your boiler or not.

Either way; act now and stop your combi boiler leaking as soon as possible! Remember, it will only get worse the longer you leave it.

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