Why is your gas boiler not working? Well, in our experience as Gas Safe registered engineers, it’s almost always down to one of a handful of common faults, and most are quick to diagnose once you know what to look for.
A boiler that won’t fire up, won’t heat your radiators, or has stopped providing hot water is never convenient, but working through a few checks first can often save you an unnecessary call out, or at least help you describe the problem clearly when you do need one.
Below, we’ve covered the most common reasons a gas boiler stops working, what you can safely check yourself, and when it’s time to call in a professional.
Check for a Gas Leak First
Before troubleshooting anything else, it’s worth ruling out a gas safety issue. If you can smell gas, hear hissing near a gas pipe, or your carbon monoxide alarm has activated, stop what you’re doing straight away. Turn off the gas supply at the meter if you can do so safely, open windows and doors, avoid using any electrical switches or naked flames, leave the property, and call the National Gas Emergency Service on 0800 111 999.
This is rare, but it’s always the first thing to rule out. Once you’re confident there’s no gas leak or carbon monoxide risk, the checks below cover the far more common reasons your boiler has stopped working.
The Most Common Reasons a Gas Boiler Stops Working
In our experience, the vast majority of “my boiler isn’t working” call outs come down to one of the following.
1. Low Boiler Pressure
Most combi boilers need to be kept at a pressure of between 1 and 1.5 bar when the heating is off. If the gauge on the front of your boiler reads below 1 bar, it will often refuse to fire up or will cut out shortly after starting. You can usually top this up yourself using the filling loop, following your boiler’s instruction manual. If the pressure keeps dropping after topping it up, there may be a leak somewhere in the system, and it’s worth getting an engineer to take a look.
2. A Frozen Condensate Pipe
Every condensing boiler has a condensate pipe, which carries waste water away from the boiler and usually runs outside to a drain. In cold weather this pipe can freeze, causing the boiler to lock out as a safety measure. If you’ve had a cold snap and your boiler has suddenly stopped working, this is one of the first things to check, and a frozen pipe can often be thawed by pouring warm, not boiling, water along its length. It isn’t something you’ll need to worry about in the middle of summer, but it’s worth keeping in mind once the colder months come round again.
3. Thermostat or Programmer Settings
It sounds obvious, but a surprising number of “boiler not working” call outs come down to the thermostat being set below room temperature, or the programmer running to a schedule you’d forgotten about. Check the thermostat is set a few degrees above the current room temperature, and that the programmer or timer is switched on for the time of day. Most homes are comfortable somewhere between 18°C and 21°C, and turning the dial higher won’t make the house heat up any faster, it will simply mean the heating stays on for longer once that temperature is reached.
4. A Power Cut or Tripped Fuse
If you’ve had a power cut recently, this can reset your boiler’s timer or programmer, meaning it’s no longer following the schedule you expect. Check your instruction manual for how to reset the clock and re-set your usual heating times. It’s also worth checking your fuse box for a tripped switch. Flick it back up gently, but if it won’t stay up or trips again straight away, this points to an electrical fault rather than something to keep resetting yourself.
5. Ignition Lockout (No Flame Detected)
Boilers are designed to lock themselves out if they try to ignite and fail to detect a flame, usually after three or four attempts. This is a safety feature rather than a fault in itself, but it does mean the boiler needs a look to establish why ignition is failing. Common causes include a low gas supply, a blocked flue, a faulty ignition electrode, or a frozen condensate pipe as above. Most boilers will display a fault code when this happens, which we’ve covered in more detail below.
6. A Problem With the Gas Supply
If other gas appliances in your home, such as your hob or gas fire, have also stopped working, the issue is likely with your gas supply rather than the boiler itself. In this case, contact your gas supplier or the National Gas Emergency Service rather than a heating engineer.
7. An Ageing Boiler or Worn Components
Most gas boilers last somewhere between ten and fifteen years with regular servicing. If yours is approaching or past this age and you’re finding yourself calling an engineer out more often, it may be more cost effective in the long run to consider a boiler installation rather than continuing to repair an ageing appliance. As a Worcester Bosch Accredited Installer, we can advise honestly on whether a repair or replacement makes more sense for your situation.
Boiler Displaying an Error Code?
Most modern boilers, including Worcester Bosch models, display a fault code on the front panel rather than simply cutting out silently. As a Worcester Bosch Accredited Installer, these are some of the codes we’re asked about most often:
- Codes starting with EA usually mean the boiler hasn’t detected a flame during ignition. This is often linked to a blocked flue, low gas pressure, a faulty ignition electrode, or a frozen condensate pipe.
- Codes starting with H are maintenance reminders rather than faults. The boiler will keep running, but it’s telling you a service is due.
- Low pressure faults (sometimes shown as a number such as 118, or as H07 on some models) simply mean the system pressure has dropped and needs topping up.
If your boiler is showing a code you don’t recognise, make a note of it before you call. It helps us understand what’s likely wrong before we’ve even arrived, and can sometimes save you a call out for something simple.
Boiler Firing Up But Radiators Staying Cold?
This is slightly different from a boiler that won’t work at all, but it’s one of the most common related questions we’re asked. If your boiler is running but one or more radiators aren’t heating up, the likely culprits are trapped air (bleed the radiator with a radiator key), a build-up of sludge and debris restricting flow, often shown by cold spots at the bottom of the radiator, or a fault with a diverter valve or pump. A power flush can clear years of built-up debris from the system and is often the fix for radiators that heat unevenly or take a long time to warm up, even when the boiler itself is working perfectly.
Quick Checks Before You Call an Engineer
- Check the pressure gauge reads between 1 and 1.5 bar
- Note down any fault code showing on the display
- Check the thermostat is set above room temperature and the programmer is running the schedule you expect
- Check the fuse box for a tripped switch
- Check whether other gas appliances in the home are also affected
- If it’s cold outside, check whether the external condensate pipe has frozen
When to Call a Gas Safe Registered Engineer
Only a Gas Safe registered engineer is legally permitted to work on the inside of a gas boiler, so if the checks above haven’t solved the problem, it’s time to call one in rather than opening up the casing yourself. This is particularly important for anything involving the gas valve, ignition system, or heat exchanger. Our team can repair most boiler faults quickly, and if you’ve been left with no heating or hot water, we treat this as a priority. For central heating faults beyond the boiler itself, such as radiators or the controls, we can look at the whole system rather than just the boiler in isolation.
Preventing Future Breakdowns
Many of the faults above become far less likely with an annual boiler service, which catches small issues like a dirty filter or a failing part before they cause a breakdown. It’s also worth having a look at your boiler controls and thermostat setup, since an outdated or poorly positioned thermostat can cause the kind of “boiler not working” symptoms covered above without there being a fault at all.
If you have a Worcester Bosch boiler, keeping the manufacturer’s ten year guarantee valid (where applicable) means having it fitted by an Accredited Installer, fitting a Greenstar System Filter, registering the boiler within 30 days of installation, and having it serviced annually by a qualified engineer. These conditions are worth checking if you’re ever in a dispute with a manufacturer over a warranty repair.
Frequently Asked Questions
Why has my boiler stopped working but I still have gas and electricity?
This usually points to a fault within the boiler itself rather than a supply issue. Common causes include low water pressure, an ignition lockout, a tripped internal fuse, or a frozen condensate pipe. Check the pressure gauge and any error code on the display first, then call a Gas Safe engineer if the problem doesn’t have an obvious cause.
Why is my boiler pressure fine but it still won’t come on?
If pressure isn’t the issue, the next things to check are the thermostat and programmer settings, followed by the fuse box. If those all look correct, the boiler may be in ignition lockout or have an internal fault such as a failed circuit board, which will need an engineer to diagnose.
Can I reset my boiler myself?
Most boilers have a reset button, and it’s usually safe to press this once if the boiler has locked out. Refer to your instruction manual for the exact location and process. However, if the boiler locks out again shortly after resetting, stop and call an engineer rather than repeatedly resetting it, as this can mask a fault that needs proper attention.
Why is my boiler noisy but not producing heat?
A loud banging or gurgling sound, sometimes called kettling, is usually caused by limescale or sludge restricting water flow through the heat exchanger. This is more common in hard water areas and often improves after a power flush and the addition of a corrosion inhibitor.
How much does it cost to repair a boiler?
This depends entirely on the fault, from a straightforward pressure top up through to replacing a major component like a circuit board or heat exchanger. We’re always happy to take a look and give you an honest, upfront price before any work begins.
Is it worth repairing an old boiler, or should I replace it?
If your boiler is under ten years old and the fault is a common, inexpensive one, repairing is usually the right call. For older boilers, or ones needing repeat call outs, a replacement is often more cost effective over time, particularly given how much more efficient modern condensing boilers are. We can talk you through the real costs of both options.
Get Your Boiler Fixed Today
If you’re still not sure why your gas boiler isn’t working, or you’d rather leave it to a professional from the start, give us a call. We’re Gas Safe registered and a Worcester Bosch Accredited Installer, covering Dorset and Hampshire including Ringwood, Verwood, Ferndown, Wimborne, Bournemouth, Fordingbridge and the New Forest.
Call Max on 07545 198220, or get in touch to book a repair.
