Why is my boiler leaking?

Is your boiler leaking water?

If you’re reading this, chances are that you have a leaking boiler. The cause could be anything from corroded pipes to excessively high pressure or loose joints. It can happen if your boiler was only installed recently, although a good Gas Safe engineer will come back to check their installation isn’t leaking.

It’s important to note that even a tiny trickle of a leak can lead to corrosion, rust or cause damage to electrical parts, so it’s vital that you spot the leak and do something about it right away.

While you’re finding out the cause of the leak, to prevent any more water leaking you should take the following steps:

• Turn off your water supply to the boiler (or if you don’t have or can’t see an isolation valve, at the mains)
• Switch off the heating
• Mop up the water
• Call a Gas Safe registered engineer

Never attempt to repair the fault yourself – you could endanger yourself and the other members of your household. Always contact a Gas Safe registered engineer to do repair work on your boiler and any other gas appliances.

Why is my boiler leaking water?

There are several reasons why you’ve spotted your boiler dripping water and you can work out what’s going on by pinpointing the exact source of the droplets.

If you don’t know where any of the following parts of your boiler are, check out our guide to how boilers work for the information you need.

My boiler is leaking water from the bottom

If your boiler is dripping water from the bottom, it could be a sign that the pipes inside your boiler have corroded. This could be a distinct possibility if your boiler is old; it’s caused by the oxygen in the water reacting with the metal of the pipes, which creates oxides or rust. The structure of a corroded pipe or tank can start to weaken over time, which could result in water leaking.

What should I do?

Call your Gas Safe registered engineer immediately; they are likely to respond quickly to calls such as: ‘water coming out of the boiler’. If the corrosion is contained in a single pipe or valve and hasn’t spread to other parts of your boiler, you might be able to get just that isolated part of the boiler replaced. If it’s more widespread, unfortunately, it’s likely cheaper to scrap your boiler and buy a new one.

When you call out your Gas Safe registered engineer, they will be able to open up the boiler, assess the situation and give you some clear advice on what to do.

While you wait for the engineer, stick a bowl, bucket or an old towel underneath the leak to stop it from doing any damage.

My pressure relief valve (PRV) is leaking

This is a simple but common issue. If your boiler’s pressure relief valve is leaking, it’s most likely that your boiler’s pressure is too high and needs to be lowered.

Your boiler’s pressure gauge (the dial underneath it that looks like a speedometer) should be somewhere between 1 and 2 bar. If the pressure rises above 2 bar, your boiler’s relief valve may start leaking water in an effort to avoid your boiler rupturing.

What should I do?

Thankfully, this is one of the boiler problems you can fix yourself. To lower your boiler pressure:

• Ensure the filling loop tap on your boiler is closed – if it’s been left slightly open, it will constantly be refilling the system and causing high pressure.
• Make sure your pressure gauge is showing it’s between 1 and 2 bar.

Bleed your radiators

• Get a radiator key (you can get them for your type of radiator from a DIY shop) and a small bucket
• Use the key to loosen the nut on the end of the radiator
• Wait until all the trapped air has escaped out of the valve and catch any water spills in the bucket
• Tighten the nut

Check out our guide to how to bleed your radiators for the full rundown.

Water is leaking from the pipes

If your gas boiler is recently been installed and is leaking water around the pipe fittings, it could be a sign of an installation fault. Don’t worry, this doesn’t necessarily mean the gas engineer you hired was a cowboy. Small water leaks are common in new boiler installations and are often hard to spot during the actual installation. This is why many Gas Safe registered engineers return a few days later to check everything’s working correctly.

What should I do?

Call your engineer to return to your home and fix the leak. In the unlikely event that you previously hired an unregistered engineer to install your boiler, call a registered one and get them to come and fix the leak.

Can I use my boiler if it’s leaking?

No. If you find or suspect a leak, or you see that the boiler pressure has dropped significantly in a short space of time, it’s probably a leak. Stop using your boiler, switch off your water supply at the mains along with the central heating, and contact a Gas Safe registered engineer.

How can I prevent my boiler from leaking?

1. An annual service

The best way to prevent your boiler from leaking water is by arranging an annual boiler service. This keeps your system in optimum health all year round – any minor issues can be dealt with by a trained professional before they turn into anything more significant – this means you can potentially avoid any serious problems for the life of your boiler.

2. Do a powerflush

A powerflush is a way of flushing your heating system with a cleansing chemical, removing any built-up limescale and debris. This could help to reduce the risk of corrosion.

View our detailed guide to carrying out a powerflush for more information.

3. Get a magnetic filter fitted

A longer term solution is to get a magnetic filter installed in your central heating system. The magnetic filter removes debris from your entire system before it has a chance to build up and affect your boiler.

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Leaking boiler FAQs

Is it normal for a boiler to leak water?

No. You will need to call a Gas Safe registered engineer straight away if you see water leaking from your boiler – it could be a sign of a major fault that could cost you a new boiler. The exception is if your pressure relief valve is leaking because there’s too much pressure, you can lower the pressure yourself.

Can I use my boiler if it’s leaking?

No. If you find or suspect a leak, or you see that the boiler pressure has dropped significantly in a short space of time, it’s probably a leak. Stop using your boiler, switch off your water supply at the mains along with the central heating, and contact a Gas Safe registered engineer.

Why is my boiler dripping water from the bottom?

No. If you find or suspect a leak, or you see that the boiler pressure has dropped significantly in a short space of time, it’s probably a leak. Stop using your boiler, switch off your water supply at the mains along with the central heating, and contact a Gas Safe registered engineer.

If your boiler is dripping water from the bottom, it could be a sign that the pipes inside your boiler have corroded. This could be a distinct possibility if your boiler is old, so call a Gas Safe registered engineer immediately.