In This Guide
Intro
Worcester Bosch boilers are among the most reliable on the UK market, but like any boiler they develop faults. Sometimes that shows as a clear symptom: no hot water, radiators staying cold, pressure dropping, or a leak. Other times the boiler puts a code on its display and locks out. This page helps with both.
Start with the common problems section if you have a symptom but no code, or jump to the fault-code directory if your boiler is showing one. Either way you will find what is likely behind it, what you can safely check, and when it needs a Gas Safe engineer. 0800 Homefix repairs Worcester Bosch boilers across London and the South East seven days a week, 365 days a year.
Common Worcester Boiler Problems
Not every fault shows a code. If your Worcester Bosch boiler is misbehaving but the display is not showing a letter-and-number code, use the symptoms below to find the likely cause before you call anyone.
|
Symptom |
Likely cause |
Where to go |
|
No hot water or heating |
Low pressure, a diverter valve fault, or a locked-out fault code |
Check the pressure gauge first; if a code is showing, see the directory below |
|
Radiators cold while the boiler runs |
Circulation pump, trapped air, or sludge in the system |
Central heating pump not working and boiler on but no heat to radiators |
|
Losing pressure or topping up often |
A leak in the system, or a failed expansion vessel or pressure-relief valve |
Needs an engineer to trace; do not keep repressurising indefinitely |
|
Water leaking from the boiler |
Varies by source; a leaking boiler should not be run |
Turn the boiler off and call a Gas Safe engineer |
|
Banging, gurgling or kettling noises |
Limescale or sludge on the heat exchanger |
Often resolved by a power flush; see the repair section below |
|
Boiler locks out or shows a code |
A specific fault the boiler has detected |
Find the code in the directory below |
|
Boiler will not fire or ignite |
Gas supply, ignition, or a frozen condensate pipe in winter |
See the EA and ignition entries in the directory below |
Directory: Worcester Bosch Fault Codes
|
Code |
What it means |
Full guide (link the anchor text, not the URL) |
|
A1 |
Pump fault — stuck, dry or airlocked circulation; can also be the flow temperature sensor |
|
|
A7 |
Hot water NTC sensor fault affecting the hot water temperature reading |
|
|
B7 |
Gas valve coil fault |
|
|
C1 |
The fan has stopped running |
|
|
C4 |
Fan or flue fault |
|
|
C6 |
Fan fault — the fan is not running correctly, affecting safe flue operation |
|
|
C7 |
Fan fault — the fan is not running or is running at the wrong speed, so the boiler cannot ignite safely |
|
|
D1 |
Return temperature sensor fault, or return temperature too high |
|
|
E5 |
Flow temperature sensor fault (measures water leaving the boiler) |
|
|
E6 |
Domestic hot water temperature sensor fault or disconnection |
|
|
E9 |
Overheat safety lockout (flow sensor / overheat) |
|
|
EA |
Flame detection failure — boiler locks out after failing to confirm ignition (includes the EA 227 no-ignition variant) |
|
|
F0 |
Internal fault — typically the PCB, ignition leads or pressure sensor |
|
|
F7 |
False flame detection — boiler senses a flame when none should be present |
|
|
H11 |
Software or firmware fault in the control unit (a maintenance code) |
How To Use Your Fault Code
Note the code exactly as it appears, including any letters, then find it in the directory above. As a general rule, a single reset is worth trying once: turn the boiler off at the power for a few seconds and back on. If the code clears and does not return, it was likely a one-off. If it comes straight back, or the code is a lockout, that is the boiler telling you the fault is still present and needs diagnosing rather than repeated resetting.
Anything involving gas, ignition, the flue or a persistent lockout is a Gas Safe job by law, not a homeowner fix.
When To Call 0800 Homefix
If your Worcester Bosch boiler keeps returning a fault code, or the code points to a gas, ignition or sensor fault, our Gas Safe registered engineers diagnose and repair it across London and the South East. See our boiler repair service for what is covered, and our rates for how pricing works: you pay for the first hour of labour in advance, with any further work quoted and agreed before it begins. We guarantee our labour for 12 months, and the manufacturer guarantees the parts for 12 months.
Helpful Resources
Spotted Any of These Warning Signs?
Our leak detection specialists cover London and the South East using acoustic detection, thermal imaging and moisture meters — no unnecessary damage, full written report, available 7 days a week.
Editorial note: This article is intended as a general homeowner guide. All plumbing work on supply pipes should be carried out by a qualified, WaterSafe-registered plumber. If you suspect a gas leak, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
