Blog25 October 2022

What are the signs of boiler failure?

Few things are more inconvenient than your boiler breaking down unexpectedly. Modern boilers are sturdier and more resilient than they were a few years ago, but even they are not infallible. A single unit will contain dozens of important components that need to work in harmony to efficiently deliver heating and hot water.

Because of this, there is still quite a lot of scope for things to go wrong – and we take a look at some of the more common reasons below:

Age and efficiency

Wear and tear are, quite simply, unavoidable. Boilers are not built to last forever but with the appropriate maintenance, a traditional gas model is designed to offer between 10 and 15 years of dependable service. In some cases, you may get two decades of use if your unit has been looked after properly and the key elements are made from high quality materials.

As time passes, boilers tend to suffer reduced effectiveness even if it is not immediately obvious that the unit itself is faltering. The clearest indicator that Father Time has caught up with your system is that there is no longer any output in the form of heating or hot water. Annual checks can help avoid – or at the very least delay – this scenario but inevitably, a replacement will always be required at some point.

Thermostat faults

Although generally considered a minor problem in terms of being addressed, thermostat malfunctions can have significant consequences for your boiler. A defective thermostat may prevent your boiler from turning on or shutting down properly, leaving you to second-guess whether or not you will actually benefit from an increase in temperature.

Once operational, you may still encounter the issue of your building becoming either too warm or too cold as the device loses its ability to accurately maintain a desired temperature. If your boiler is underperforming, an engineer will typically check the thermostat before anything else.


Leaks are rarely a good sign – and there’s a reason for that. If you notice water seeping through your unit, it’s quite likely that something serious is amiss. There are a number of potential causes of a leak, with unwelcome side effects in each case. Stress cracks or loose joints accentuated by old age often lead to leaks, as do malfunctioning pressure relief valves.

In some cases, a successful repair can be carried out if the origin of the leak is identified early enough.


If your building’s central heating system starts suddenly making a rattling sound, then there’s a good chance that internal components are vibrating against once another. Sometimes, this rattling noise can be attributed to air building up in the pipework but this can normally be fixed fairly easily by bleeding a radiator. If the noise persists despite you taking this step, it may imply that a valve is loose.

An unexplained noise should never be disregarded. At best, it can be annoying, but at worst, there is a possibility that it signifies something dangerous. Limescale build-up and blocked or faulty heat exchangers are also likely to cause your boiler to whistle or clang, so it’s best to contact a professional if you hear something unusual.


Although an extension of the previous point, kettling occurs when an accumulation of limescale creates hot spots inside your system. This is more frequently seen in hard water regions, with limescale attaching itself to components and pipework and allowing the formulation of steam bubbles. Depending on the severity of the issue, these steam bubbles will pop, creating a high-pitched kettling noise.

Generally speaking, you should expect to have to replace either your heat exchanger or the entire boiler system if you find yourself in this situation.

Frozen condensate pipe

This is particularly prevalent during the colder season when your boiler is most needed! The system works by transporting condensate from your boiler to outside but when ambient temperatures are lower, the condensate can freeze and cause a blockage. If the condensate pipe is fitted externally, then you are much more likely to contend with an obstruction that will ultimately cause your boiler to break down.

Low pressure

You can ascertain whether your boiler’s pressure is too low by consulting the built-in pressure gauge. Ideally, this should be set at around 1.5 bar. If your reading is 1 or lower, it is very unlikely that your boiler has been functioning at full capacity.

Low pressure can be caused by a leak, recently bled radiators or a failed internal component, so you can start by looking for visible signs that one of these things have occurred. Under no circumstances should you attempt to disassemble your unit or remove any protective casings. If no leak is discovered, you can try repressurising your boiler.

Despite your best intentions, there are some occasions where pre-emptive measures have been unsuccessful and a temporary boiler is required in the short-term.

As the UK’s leading supplier of electric, gas and oil-fuelled boilers, we are naturally the first port of call for businesses that have been affected by an untimely boiler breakdown. Our expertise had been demonstrated across a range of projects and been a significant contributing factor in us working alongside some of the biggest clients in virtually every industry.