Smell gas?
Open windows, don't touch electrical switches, leave the property and call 0800 111 999 (National Gas Emergency Service, free 24/7).
Common Boiler Problems & Troubleshooting Steps
No hot water or heating
Before calling an engineer, check:
- • Thermostat: Is it set above room temperature? Try turning it up a few degrees.
- • Timer/programmer: Is it set to the right time and on the correct schedule?
- • Boiler pressure: Check the gauge. It should read between 1 and 1.5 bar. If it's below 1, repressure using the filling loop.
- • Power supply: Has the boiler's fuse or circuit breaker tripped? Check your fuse box.
- • Gas supply: Are other gas appliances working (cooker, gas fire)? If nothing works, check your prepayment meter hasn't run out.
Still not working? Book a repair and I'll diagnose the fault.
Boiler losing pressure
If your pressure gauge is below 1 bar:
- • Repressure: Find the filling loop. It's usually a silver braided hose or a small tap underneath the boiler (check your manual if you're not sure). Open it slowly until the gauge reads 1-1.5 bar, then close it.
- • Check for leaks: Look under radiators, around valves, and under the boiler for any drips.
- • Recently bled radiators? Bleeding radiators releases pressure. Repressure after bleeding.
If the pressure keeps dropping after repressuring, there's likely a leak somewhere in the system that needs professional repair. Book a repair.
Boiler showing an error code
Most boilers display error codes when something's wrong:
- • Try a reset: Hold the reset button for 5-10 seconds. Some faults are temporary and a reset clears them.
- • Check your manual: The error code meaning is listed in your boiler manual (most are also available online, just search your boiler model + error code).
- • Persistent code? If the error keeps coming back after a reset, it needs professional diagnosis.
Don't keep resetting a boiler that keeps faulting, it could make the problem worse. Book a repair and I'll find the root cause.
Strange noises (banging, kettling, gurgling)
Different noises mean different things:
- • Banging/kettling: Usually caused by limescale buildup or sludge in the heat exchanger. Needs a powerflush or repair.
- • Gurgling: Air trapped in the system. Try bleeding your radiators, starting with the one furthest from the boiler.
- • Humming: Could be the pump running too fast. Adjusting pump speed may fix it, but this needs an engineer.
Noisy boilers rarely fix themselves. Book a repair before it gets worse.
Frozen condensate pipe (winter)
In cold weather, the condensate pipe (white plastic pipe running outside) can freeze:
- • Pour warm water (not boiling) over the frozen section of the external pipe
- • Reset the boiler once the pipe has thawed
- • Insulate the pipe to prevent it happening again. Pipe lagging from any DIY shop works
If you can't find the pipe or it keeps freezing, I can reroute it to prevent future issues. Book a visit.
Common Boiler Error Codes by Brand
Here are the most common error codes I see on callouts. If your boiler is showing one of these, try a reset first (hold the reset button for 5-10 seconds). If the code comes back, it needs professional diagnosis.
Worcester Bosch (Greenstar range)
EA 227: Ignition failure. The boiler has tried to light and failed. Can be caused by a faulty gas valve, blocked burner, or electrode issue. Try resetting once. If it returns, book a repair.
EA 229: Flame lost during operation. The boiler lit but the flame went out. Often a gas supply issue or faulty flame sensor. Do not keep resetting repeatedly.
D5: Low water pressure detected. Check your pressure gauge. If it's below 1 bar, repressure using the filling loop. If it keeps dropping, there's likely a leak.
E9: Safety temperature limit reached. The boiler has overheated. Can be caused by a pump failure, sludge buildup, or blocked heat exchanger. Needs professional diagnosis.
A1: No hot water from a combi boiler. Usually a diverter valve issue. Needs an engineer.
Vaillant (ecoTEC range)
F28: Ignition failure. The most common Vaillant fault. Can be gas supply, ignition lead, electrode, or gas valve. Reset once. If it persists, do not keep trying.
F75: Pressure sensor fault. The boiler cannot detect a pressure change when the pump starts. Often caused by a faulty pump or pressure sensor. Common on older ecoTEC models.
F22: Low water pressure. The boiler has detected pressure below the minimum. Repressure using the filling loop. If it drops again within a few days, there's a leak somewhere.
F27: False flame detection. The boiler thinks it can see a flame when there isn't one. Usually a faulty flame sensor or PCB issue. Needs an engineer.
F29: Flame extinguished during operation. Similar to F28 but happens mid-cycle. Often a flue or gas supply issue.
Ideal (Logic, Vogue, Esprit range)
L2 (or F2): Ignition lockout. The boiler failed to ignite after multiple attempts. Gas valve, electrode, or burner issue. Reset once and monitor.
L1 (or F1): Low water pressure. Pressure has dropped below 0.5 bar. Repressure via the filling loop to between 1 and 1.5 bar.
L5: False flame. The PCB is detecting a flame signal when the boiler should be off. Usually a PCB fault. Needs professional diagnosis.
L8: Return thermistor fault. The sensor reading the return water temperature has failed. Needs replacement.
LC: Pump fault or no circulation. The boiler is firing but water isn't moving through the system. Could be a seized pump, airlocked system, or blockage.
Baxi / Main
E133: Ignition fault. Gas supply issue, faulty electrode, or gas valve problem. The most common Baxi error code. Reset once.
E119: Low water pressure. Repressure the system. If it keeps dropping, check for leaks at radiator valves, connections, and under the boiler.
E125: Circulation fault. No flow detected. Could be a pump failure, airlock, or system blockage. Often accompanied by banging or gurgling noises.
E110: Overheating. The boiler has hit its safety temperature limit. Can be sludge in the heat exchanger, pump issues, or a blocked system. Do not reset repeatedly.
E160: Fan fault. The fan isn't running at the correct speed. Needs professional diagnosis, usually a fan or PCB replacement.
Viessmann (Vitodens range)
F4: Ignition failure. Similar causes to other brands, gas supply, electrode, or valve. Reset once via the OK button.
F5: Flame lost during operation. Flue issue, gas pressure drop, or faulty flame detector.
F2: Burner lockout. The boiler has locked out for safety. Needs a reset and investigation if recurring.
B1 or 0C: Low pressure warning. Repressure the system. Viessmann boilers often show a bar graph rather than a numeric code for pressure issues.
Glow-worm (Energy, Easicom range)
F1: Low pressure. Repressure to 1-1.5 bar.
F4: Ignition failure. Gas supply, electrode, or valve issue.
F9: Fan speed fault. The fan isn't reaching the required RPM. Needs professional diagnosis.
F22: Dry fire. The boiler has fired without sufficient water flow. Potentially dangerous. Do not reset. Call an engineer.
Alpha (E-Tec, InTec range)
E10: Low pressure. Repressure the system.
E20 or E28: Ignition failure. Reset once. Persistent faults usually mean a gas valve or electrode issue.
E40 or E41: Flue blockage or fan fault. The boiler cannot verify safe flue gas discharge. Do not attempt to fix yourself.
If your error code isn't listed here, check your boiler manual or search online for your specific model and code. If the error keeps returning after a reset, don't keep trying. Book a repair and I'll diagnose the root cause.
When to Call a Gas Engineer
If the checks above haven't solved the problem, it needs professional diagnosis. I'll find the fault, explain what's wrong, and give you the cost to fix it before starting any work. No surprises.
I cover Haverhill, Saffron Walden, Linton and Newmarket. Book a repair online or send me a message.