Common Causes of Boiler Breakdowns and How to Avoid Them

Boilers break down when you least expect them to, and usually during the colder months when you’re most dependent on them. Boilers can stop working for any number of reasons, so it’s important to use them regularly and schedule annual servicing.

Before you start shopping for a new boiler when one stops working, look for some simple explanations – is a valve closed? Is the gas on? Has a fuse blown? Is the thermostat set up wrong? Try to locate the source of the problem before trying to fix it.

Here are some of the most common causes of boiler breakdowns:

Age of boiler

Boilers over ten years old are more at risk of breaking down. Rust and corrosion build up and spread over time, and when combined with regular stress on pipes and components, can lead to multiple leaks and failures. Leaking is usually due to the corrosion of an internal component, and should always be handled by a gas-safe engineer.

Dirt and debris also accumulate and restrict water from flowing efficiently, or can stop the boiler working altogether. To ensure your boilers live long and healthy lives, it is imperative that you schedule regular servicing.

·         Symptoms: Leaking, strange noises, regular failures.

·         How to fix: If a boiler is completely worn out, it needs replacing.

·         How to prevent: Regular servicing and maintenance.

Common Causes of Boiler Breakdowns - testing boiler

Frozen external pipes

The plastic condensate pipe that transports acidic water away from a boiler to the outside of the property can freeze in cold weather and stop the boiler from working. Inactivity during warm months, and the strain of going from one temperature extreme to the other can make this worse.

·         Symptoms: No hot water or heating, gurgling sounds from the boiler.

·         How to fix: Pour hot (not boiling) water over the pipes until they thaw. Hot water bottles can be used on sections of pipe that require heat for longer periods.

·         How to prevent: Cover and insulate your external pipes, or put the heating on at around 13 degrees during winter if nobody’s home. This may seem like a waste of money, but it will save you from the far worse consequences of a burst pipe.

Common Causes of Boiler Breakdowns - frozen pipes

Faulty diverter valve

On combi boilers, the diverter valve opens and closes depending on whether your tenants require central heating or hot water. If you’ve attempted to fix the diverter but the heating still isn’t working properly, there may be a build-up of sludge in the radiators, which an engineer can chemically flush out.

·         Symptoms: Getting hot water but not heating, getting heating but not hot water, or only getting hot water when the heating is on.

·         How to fix: Call a gas-safe registered engineer to fix or replace the valve.

·         How to prevent: Schedule regular maintenance.

Common Causes of Boiler Breakdowns - dirty valves

Damaged pump or pump seal

 Many issues can occur with a boiler pump, including leaking, airlock, gathered sludge, and jammed propellers. Pumps should last at least 15 years, but can wear out faster if used excessively. Make sure the boiler pressure isn’t too high, as this could be the cause of leaking.

·         Symptoms: Poor heat output, only some radiators working, unusual noises from boiler, no noises at all, leaking, failure to start.

·         How to fix: Some small fixes may be handled yourself, but if you’re uncertain it’s always best to call out an engineer.

·         How to prevent: Schedule regular maintenance.

Common Causes of Boiler Breakdowns - damaged pump

Low water pressure

 A boiler usually has low water pressure if there is a leak in the system, or if a radiator has recently been bled. Check the pressure gauge; if the needle is below 1, your heating won’t function properly.

If the boiler pressure changes sporadically, it may have a leak, or a faulty pressure relief valve. If so, this will need replacing.

·         Symptoms: Heating does not function properly.

·         How to fix: If you are aware of a leak, call out an engineer. Otherwise, repressurise the boiler.

·         How to prevent: Regular servicing to avoid leaks and maintain valves.

Common Causes of Boiler Breakdowns - low water pressure

Thermostat malfunctions

If the thermostat can’t communicate efficiently (for example, if it is set to the wrong time and date), the boiler may not switch on when it is expected to. Basically, if the thermostat doesn’t work, neither will the heating. The boiler won’t be able to detect the temperature of the water and will shut itself off to prevent overheating or assume it is already at the required temperature.

·         Symptoms: Heating not coming on at all/when expected.

·         How to fix: Replace batteries, check the right time and date are set. Clean and/or adjust the thermostat. If it still doesn’t work, you may need to replace it.

·         How to prevent: Regularly clean the thermostat and replace batteries.

Common Causes of Boiler Breakdowns - thermostat


Most common in areas of hard water, limescale build-up restricts the flow of water and causes water to overheat and boil. This is known as kettling.Kettling will shorten the life of a boiler as it is forced to work harder and therefore costs more to run.

·         Symptoms: Sound similar to a boiling kettle.

·         How to fix: Call an engineer to powerflush the system.

·         How to prevent: Invest in water softeners and scale reducers, installed by a gas-safe engineer.

Common Causes of Boiler Breakdowns - limescale

Thermocouple malfunction

 If your boiler is quite old and the pilot light keeps going out, there is a chance that the thermocouple (gas valve safety device) is faulty. Debris may have built up around the pilot, preventing the thermocouple from sensing a flame.

·         Symptoms: Pilot light won’t stay lit/error code.

·         How to fix: You can adjust and clean this yourself, but if this doesn’t fix the issue, then the thermocouple needs replacing.

·         How to prevent: Clean and maintain the thermocouple.

Common Causes of Boiler Breakdowns - malfunction

As you may have seen, the prevention for many of the common causes of boiler breakdown is to schedule an annual servicing. Put simply, it’s best to pay for an engineer to prevent boiler issues than to pay for an engineer and replacement parts once damage has occurred. If you are experiencing boiler breakdown, try to identify the issue and see if there is a simple solution. Regardless, if you don’t feel comfortable attempting the fix yourself, it is always safer to call out an engineer.

 0800 Repair Gas repair and service boilers in Durham and the North East. If a boiler is in need of fixing, mending, or overhauling, call them today on 0800 114 3485.