Heating not working? A troubleshooting guide

When your heating system fails, it is more than an inconvenience; it is an urgent problem that impacts comfort and safety, especially during colder months. Many common heating issues can be resolved with simple troubleshooting steps, potentially saving you the cost of an unnecessary engineer call-out. This guide provides clear, actionable steps to diagnose and potentially fix a broken heating system in your home.

Fuse Energy empowers customers with knowledge and control during a heating emergency. While we do not offer repair or maintenance services for existing boilers (we do install the Vaillant ecoTEC Plus model), our 24/7 human customer support is a reliable first point of contact for energy-related queries, helping you navigate stressful situations with clear, authoritative guidance. Click here to switch to Fuse Energy today.

Why your heating is not working: common causes

Understanding why your heating has failed is the first step to getting it back on. Several issues can prevent your central heating from working correctly.

Thermostat or timer issues

Incorrect thermostat or programmer settings are a frequent culprit. Your system might be set to the wrong mode (e.g., summer mode), the timer could be off, or the thermostat might not be calling for heat.

Low boiler pressure

Low boiler pressure is a common cause of heating system failure. For most sealed central heating systems, the pressure gauge should sit around 1 to 1.5 bar when the system is cold. If the needle is below 1 bar, your boiler may stop working or display a fault code to protect itself.

Frozen condensate pipe

Modern condensing boilers produce acidic water called condensate, which drains away through a plastic pipe. In cold weather, this pipe can freeze, especially if it runs outdoors or through an unheated space. A frozen condensate pipe can prevent a condensing boiler from working, causing it to shut down or malfunction.

Pilot light or ignition problems

If your boiler has a pilot light, it might have gone out. For modern boilers, ignition problems can be caused by a fault within the system preventing it from firing up.

Radiator airlocks or valve issues

Trapped air in radiators blocks the even circulation of hot water, reducing heating efficiency and causing cold spots. Radiator valves that are closed or stuck can also prevent heat from reaching specific radiators.

Boiler lockout or fault codes

Boilers are designed to 'lock out' for safety if they detect a fault. This often results in a specific fault code or flashing light on the boiler's display. These codes indicate a problem that needs attention.

No hot water but heating works

If you have heating but no hot water, or vice versa, it often points to an issue with a diverter valve inside your boiler, especially in combi boilers. This valve controls whether hot water goes to your taps or your radiators.

Immediate checks: your step-by-step troubleshooting guide

Before calling a professional, run through these basic checks. Many heating problems can be resolved quickly.

Check your thermostat and programmer

Ensure your thermostat is set to the 'heating' mode and the temperature is higher than your current room temperature. Check your programmer or timer to confirm it is set to 'on' for heating and within the correct time period. A simple adjustment here can often solve the problem.

Verify boiler power and reset

Make sure your boiler is switched on at the mains. Check if any fuses have tripped. If your boiler has a pilot light, ensure it is lit. If not, consult your boiler manual for instructions on how to relight it safely. Many boilers also have a reset button; pressing this can sometimes clear minor faults.

Inspect boiler pressure and top up

Locate the pressure gauge on your boiler. It should typically read between 1 and 1.5 bar when the system is cold. If it is below 1 bar, you will need to repressurise the system using the filling loop or built-in key, following your boiler's instructions. Stop once the pressure is back in the recommended range.

Bleed your radiators

If some of your radiators are cold at the top but warm at the bottom, they likely have trapped air. Bleeding radiators can improve heating efficiency by removing this air, allowing hot water to circulate properly. You will need a radiator key and a cloth. Turn off your heating, wait for the radiators to cool, then open the valve at the top of the radiator until air hisses out, followed by a steady stream of water. Close the valve, then check your boiler pressure and top it up if needed.

Thaw a frozen condensate pipe safely

If your condensing boiler has stopped working during cold weather and you hear gurgling noises, check the external condensate pipe (usually a white plastic pipe exiting your wall) for ice. If it is safe to reach, you can thaw it by pouring warm (not boiling) water over the frozen section or applying a hot water bottle. Once thawed, the boiler should reset itself.

Check your gas or oil supply

Ensure your gas supply is on at the mains. If you have a prepayment meter, check that you have sufficient credit. For oil-fired systems, verify that your oil tank is not empty.

When to call a professional engineer

If basic troubleshooting does not resolve the issue, or if you suspect a more serious problem, it is time to call a professional. All gas boiler work in the UK must be carried out by a Gas Safe registered engineer. It is illegal and dangerous for unqualified individuals to attempt complex repairs.

Understanding boiler fault codes

If your boiler displays a fault code, note it down. While some manuals offer basic troubleshooting for codes, many indicate internal faults that require a Gas Safe registered engineer to diagnose and fix.

Persistent issues after basic checks

If you have gone through all the immediate checks and your heating still is not working, or if the problem recurs frequently (e.g., constant low pressure), professional intervention is necessary.

Gas leaks or safety concerns

If you smell gas, hear a hissing sound near your boiler or gas meter, or notice a yellow/orange flame (instead of blue) from your boiler, turn off your gas supply immediately, open windows, and contact the National Gas Emergency Service on 0800 111 999. Do not attempt to fix it yourself.

Annual boiler servicing and maintenance

Regular boiler maintenance is crucial for efficiency and longevity. An annual service by a Gas Safe registered engineer can identify potential problems before they lead to breakdowns and ensure your boiler operates safely and efficiently.

Preventing future heating problems

Proactive maintenance and understanding your system can help avoid future heating emergencies.

Regular boiler servicing

Schedule an annual service with a Gas Safe registered engineer. This is not only a legal requirement for landlords but also highly recommended for homeowners to keep your system running smoothly and safely.

Understanding your heating system

Familiarise yourself with your boiler manual, thermostat, and programmer. Knowing how your system works can help you quickly identify and address minor issues.

Insulating your home

Good insulation reduces heat loss, making your heating system more efficient and less prone to overworking. This includes loft insulation, cavity wall insulation, and ensuring windows and doors are well-sealed.

A broken heating system is stressful, but Fuse Energy is here to help you manage your home energy. While Fuse Energy does not offer boiler repair or maintenance services for existing boilers, we do offer installations of the Vaillant ecoTEC Plus gas boiler. Our 24/7 human customer support team is available to assist with any energy-related queries you might have during a heating emergency. We can provide guidance and support, helping you understand your energy usage or supply, even if the ultimate fix requires a specialist. The Fuse app gives you control over your energy, allowing you to monitor your usage, manage your account, and access support, empowering you with the information you need to make informed decisions about your home energy. The average UK home uses around 9,500 kWh of gas per year for heating and hot water. Managing this usage effectively starts with a reliable and well-maintained heating system. Click here to switch to Fuse Energy today and take control of your home energy. You can also learn more about our mission to make energy simpler and greener by clicking here.