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7 Reasons Why Your Boiler is Leaking Water

Anyone who’s had to deal with a leaking boiler before will know how frustrating this problem can be, and unfortunately, there can be a wide number of reasons for why your boiler is actually leaking in the first place. We’ve covered some of the most likely reasons here.

The three most commonly installed boilers in homes in the UK are the Combination Boiler, System Boiler, and a Regular Heat Only Boiler. Unfortunately, regardless of the type of boiler you have in your home, leaking or dripping boiler is a common occurrence and something you’ll want to address as soon as possible.

If your boiler is leaking water, the first thing to do is turn off the water supply. The leaking water could cause corrosion or even cause electrical parts to malfunction, so this should be your first priority.

At the same time, you’ll want to empty the remaining water in the boiler system. Refer to the boiler manual to understand what might be causing the water leak.

Why is my boiler leaking?

Here are six possible likely reasons that your boiler may be leaking.

1. There is a leak from the bi-thermal heat exchanger between the heating and hot water bodies

2. The expansion tank has failed. Watch the boiler as the water heats. If the leak starts after the boiler burner has run for a while, then you most likely have a faulty expansion tank.

3. It is possible that the boiler safety valve is faulty. A build-up of limescale and calcite in the tank and pipes, will increase the water pressure in the tank, and cause leaks.

4. The pressure relief valve setting may be incorrect (the normal pressure setting is 1.5 bar). Excess pressure causes the valve to open. Once this happens, you will have to replace the valve.

5. Corrosion of the pipes, boiler tank, or valves will weaken the metal and cause the water to leak. Minor repairs can resolve the problem, but if the corrosion is widespread, you may need to have the tank replaced or buy a new boiler.

6. Poor installation, in particular bad soldering along with the copper fittings, will cause the water to drip. If you have inherited a badly installed boiler system, re-installation may be the best solution.

7. A leak from seals on internal parts could cause a leaking boiler, especially if these seals are old and corroded.

What should I do if my boiler is leaking?

It may not be easy to diagnose the actual source of the water leak from the boiler system. Left unattended a dripping boiler can result in mildew and fungus, and damage the structure of your home. Call a Gas Safe Registered Engineer to carry out a full inspection and any repairs.

You should always use a heating engineer to repair your boiler – don’ try to mess around with it yourself if you are not qualified.


Important: Boilers are among the most expensive items you have in your home. Regular annual by a qualified technician will save you the cost of expensive boiler system repairs later on.