Your boiler is the backbone of your home’s central heating system, especially in cold weather. But like any appliance, boilers are susceptible to wear and tear and can experience a range of issues that interrupt heating and hot water supply.
To help you tackle these issues, we've outlined 10 of the most common boiler problems, their possible causes, and steps you can take to address them.
If any of these issues seem complex, JustFix connects you with qualified, local heating engineers who can safely and efficiently repair or service your faulty boiler.
10 common boiler problems and solutions
Understanding the most common combi boiler issues can save you time and help you decide whether you can handle a quick fix or need help from a Gas Safe engineer. Here are ten frequent problems you may encounter with your boiler, along with practical solutions and tips to keep your heating system running smoothly.
1. The pilot light keeps going out
The pilot light is the small, continuously burning flame that ignites your boiler when heat or hot water is needed.
If your pilot light keeps going out, you might face a lack of hot water or heating, and there are a few possible reasons for this.
One common cause is a draught blowing the light out. Another possible reason is a faulty thermocouple—a component that regulates gas flow and ensures safety by detecting temperature changes in the pilot light.
Older boilers with pilot lights are more prone to this issue, as newer combi boilers typically ignite electronically.
What you can do
First, check if other gas appliances in your home are functioning correctly. If not, you may have a gas supply issue, and it’s essential to contact your gas supplier.
If your other gas appliances work, consult your boiler manual and follow the instructions to reignite the pilot light safely. If the problem persists, it could be a sign of a faulty thermocouple, and a qualified heating engineer can diagnose and repair the issue.
2. The boiler is making noises
Boilers can make various noises that may indicate underlying issues. Gurgling, whistling, or banging sounds are often due to trapped air in the heating system, low boiler pressure, or a failing pump.
A noisy boiler can sometimes indicate frozen condensate pipes or a buildup of mineral deposits. The type and location of the noise can give clues about the problem, but unusual sounds should never be ignored.
To better understand these sounds, check out our comprehensive guide to boiler noises.
What you can do
Bleeding your radiators can help release trapped air that may be causing the gurgling sound. If you need more help, read our step-by-step guide on how to bleed your radiators.
For banging or vibrating noises, inspect your boiler’s connectors and settings, but if the noise doesn’t go away, it’s wise to contact a local engineer.
Unusual noises can sometimes signal a more serious internal issue that may lead to a boiler breakdown if not addressed promptly.
3. No heating or hot water
When your boiler fails to provide heating or hot water, it could be caused by various issues, including the boiler's pressure, a faulty diverter valve, or an issue with the boiler’s thermostat.
This problem is especially common in older boilers that may not regulate pressure as effectively as modern models. However, even new boilers can experience such issues due to unexpected component failure.
What you can do
Start by checking the pressure gauge on your boiler to see if the reading is within the recommended range (usually between 1 and 2 bars). Verify your thermostat settings as well, and make sure the power supply is active.
For persistent issues, it’s best to consult a gas engineer who can inspect the boiler’s internal components and make any necessary repairs.
Alternatively, if your heating is working but you have no hot water, see our full guide on what to do.
4. Boiler leak
A leaking boiler can indicate a serious issue, as even a small drip could lead to significant damage over time. Common causes include a faulty pump seal, a broken pressure relief valve, or internal corrosion.
If you see water pooling around the boiler, it’s critical to act quickly, as leaks can damage internal components and reduce the boiler's lifespan.
Learn more about the potential causes of a leaking boiler in our full guide.
What you can do
Turn off the water supply to your boiler to prevent further leakage.
While it’s essential to address a leak promptly, you should never attempt a DIY repair on a leaking boiler, as this could void your warranty and pose safety risks.
Contact a Gas Safe registered heating engineer through JustFix to repair the leak and ensure your boiler operates safely.
5. Low boiler pressure
Boiler pressure that’s too low can prevent hot water circulation, leaving your radiators cold and impacting your home’s heating system.
Low boiler pressure can result from a water leak, recent radiator bleeding, or a failing pressure relief valve.
The pressure gauge should ideally read between 1 and 2 bars; if it’s below this level, your boiler may struggle to heat water efficiently.
What you can do
Check the system for any leaks, as this could explain the pressure drop. If no visible leaks are present, you can carefully re-pressurise the boiler using the filling loop (following the instructions in your boiler manual).
If re-pressurising doesn’t work, contact a qualified heating engineer through JustFix to assess the system and repair any internal faults that may be causing the low pressure.
6. Radiators are cold
Cold radiators can indicate trapped air, a sludge buildup, or a faulty pump. If your radiators are only warm at the bottom, it’s likely due to sludge or air buildup in your central heating system.
If your radiator is warm at the top but cold at the bottom, it’s a sign that something is obstructing the flow of hot water in the radiator’s lower sections. This can reduce heating efficiency, leading to increased energy costs.
If your radiator is fully cold, it indicates a potential issue with the boiler, thermostat, or central heating system that requires attention.
What you can do
Start by bleeding your radiators to release any trapped air. If they’re still cold, your system may need a power flush, which a professional should do to remove sludge buildup.
An accredited heating engineer can safely flush your system and restore optimal heating performance in your home.
7. Boiler is kettling
Kettling occurs when limescale or sludge accumulates in your boiler’s heat exchanger, restricting water flow and causing a “kettling” sound.
This is especially common in areas with hard water, as mineral deposits can build up more quickly, leading to higher heating costs and potential internal damage.
Find out if you live in a hard water area and how to prevent limescale with our comprehensive guides.
What you can do
If you hear a kettling noise, it’s best to contact a Gas Safe registered engineer to perform a professional system flush.
This will clear out sludge or limescale deposits, improving efficiency and preventing long-term damage.
8. The boiler is not responding to the thermostat
A faulty thermostat can lead to inconsistent heating and an unresponsive boiler. This can result from outdated thermostat settings, dead batteries, or a wiring issue.
Some thermostats can lose calibration over time, which may prevent them from correctly regulating the temperature.
What you can do
Double-check the thermostat settings and replace the batteries if it’s wireless. Ensure the thermostat is in an accessible, accurate location—away from heat sources or cold drafts that could throw off its readings.
If the thermostat is still not working, consider upgrading to a modern, programmable thermostat. A heating and gas engineer can help with installation and calibration.
9. Frozen condensate pipe
A frozen condensate pipe can block the condensate’s flow to an external drain, leading to boiler shutdown. This is a common issue in freezing temperatures, particularly with condensing boilers that produce acidic condensate.
A frozen pipe can also cause unusual noises or trigger a fault code on the boiler display.
What you can do
Use warm water, a hot water bottle, or a warm cloth to thaw the pipe carefully—never use boiling water, as it can damage the pipe. Our guide on thawing a frozen condensate pipe provides detailed steps.
10. The boiler keeps switching off
Low pressure, thermostat issues, or a blocked heat exchanger can cause frequent shut-offs.
When your boiler keeps turning off, it can affect the entire heating system and may indicate a deeper problem with one or more internal components.
What you can do
Check the pressure and thermostat as suggested in issues #5 and #8. If adjusting the thermostat and re-pressurising doesn’t work, there could be a blockage or another underlying fault that requires professional attention.
A JustFix gas engineer can diagnose and repair the issue, ensuring your heating system runs smoothly.
You can also see our full guide on what to do if your boiler won't turn on.
Still having boiler problems?
Dealing with boiler problems can be frustrating and time-consuming. If you need a reliable fix, JustFix can connect you to local, qualified heating engineers for all types of boiler repairs and annual servicing.
Simply fill in a few details on the JustFix app, and you’ll be matched with a Gas Safe registered engineer who can resolve your boiler problems quickly, safely, and affordably.
Whether you need boiler servicing in Barnet or next-day boiler repair in Woking, our network of qualified professionals can get your boiler up and running again in no time.
