Boiler Leaking Water from Bottom (Causes & Fixes)

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Combi-boilers can spring a leak for a number of reasons and depending on where the leak is, the costs of parts and labour can soon add up.  However, in some circumstances, with a little know-how and adjustments, there may be a more cost-effective solution.

This article will help to identify the reason behind the leak and make suggestions for ways to fix the issue.

Water leaking from underneath the boiler

When water is leaking from under the boiler unit, it is likely that the pipes immediately underneath are causing the issue. Any such leaks should be dealt with urgently as they could develop into a more serious matter.

Over time copper pipework can erode due to the constant use of water and metallic debris running through the system and pipework, resulting in small gaps forming and water leaking through them.

Another common issue is that following installation, the pipework joints leak due to incorrect fitting.  Installers can easily miss potential leak areas during installation; however, any conscientious engineer will usually return, checking for leaks and fixing any issues.

To be certain that the pipework is the issue, undertake a visual check underneath the boiler to confirm the location of the leak.  If the source is the pipework, you will require a qualified gas engineer to fix the issue.  Do not try and make any amendments yourself.

In the meantime, try to contain the leak either by using containers to capture the drips or by wrapping the leaking pipework with cloths.

If your boiler is over ten years old, pipework corrosion can be the beginning or the end of the use of the system.  With every issue, depending on the age of the boiler, it is worth weighing up the costs of repairing versus replacing the unit.

If you need to reset your boiler too often, it may be a sign of a more significant fault, such as a faulty PCB, a central heating pump problem and if your boiler isn’t firing up for central heating or your boiler isn’t igniting, it may be time to consider getting a new boiler quote.

Top causes of a boiler leaking from the bottom 

#1 Cause: High Pressure

 As a boiler heats the water temperature to provide heating around the property via radiators or hot water from taps, the water expands, increasing pressure in the boiler.  Luckily most boilers feature pressure gauges to enable easy identification of the pressure levels inside the unit.

Most combi-boilers when on standby, should typically be around 1 bar of pressure. During use, anything above 2 would highlight an over pressurised boiler. The consequences of high pressure inside the boiler are that the pressure release valve or PRV will release the excess water.  If this doesn’t happen the internal parts will fail.

With this concern, there are steps that can be taken to reduce the pressure on the system.  Firstly, check that the boiler filling loop tap is firmly closed.  To test that the taps are closed, turn the taps in one direction and notice if the pressure increases, if not they are closed, just ensure that the taps are firmly closed.

The next step is to bleed the radiators.  To do this firstly ensure that the system is off and cool. Next, you will require a bleed key to loosen the nut at the end of a radiator.  You may also require a container to collect any water that is released when bleeding the radiators.  If you are nervous, try looking up a video on how to bleed radiators, before you start.

#2 Cause: Corrosion and system wear and tear

Over time water and debris, including limescale can damage and corrode boiler parts and the associated system pipework. An engineer would be required to assess the condition of the boiler and parts from such wear and tear damage.

The recommended approach is to book an annual service of the boiler by a gas safety engineer to monitor the condition of the boiler and its parts. This may also provide notice that parts require replacing before an emergency breakdown is incurred.

As already mentioned, the age of the boiler would direct the best approach, either to fix or replace. Should the unit be more than 10 years old, generally the advice would be to replace the boiler. Often modern units are more energy-efficient and therefore a benefit of replacement is saving on heating bills.

#3 Cause: Leaking or faulty heat exchanger

The suspicion of a faulty heat exchanger would need to be confirmed via inspection by a gas safety engineer as it is not possible to determine visually from outside the unit.

Unfortunately, the heat exchanger is one of the most expensive parts within a boiler and can breakdown or fault over time. Due to the cost, a replacement heat exchanger may not be economically viable and therefore a replacement boiler may be recommended. A safe gas engineer should be able to advise the best approach in this situation.

Related boiler problems:

#4 Cause: Leaks from seals on internal parts

Wear and tear can also occur on the seals internally within the boiler unit, causing leaks.

A visual check can be undertaken by taking off the cover from the boiler and visually inspecting inside for any signs of water. However, if you are not confident with removing the cover, a qualified engineer should monitor this during an annual service.

If anything is noticed, a gas safety engineer should be able to fix small issues with a suitable sealant.

Is your boiler losing power? Or is your boiler pressure too high? If your boiler is old, past its warranty, it may be time for a new boiler replacement.

Preventative measures to avoid issues with a combination boiler

If you are in a hard water area, limescale can be a big issue therefore the use of scale inhibitors can be useful to prevent damage to the boiler. There are also deep cleaning options such as the use of chemical system flushes to provide as-hoc thorough system cleaning to prevent debris build-up that can result in boiler breakdowns.

In addition, regular servicing can monitor the condition of your boiler, highlighting any detrimental changes that may require attention to prevent a breakdown.

Boiler brand faults: 

Boiler leaking from bottom conclusion

Wear and tear issues are likely to occur over time with combination boilers however with regular servicing and maintenance these can be minimised. Unfortunately, boilers tend to have a 10-year life expectancy and following this repair costs can add up, therefore replacement is often deemed more appropriate.

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