Worcester Bosch is one of the most trusted boiler brands in the UK — but even the best boilers can throw up a fault code when something goes wrong. Understanding what these codes mean can save you an expensive call-out and help you fix the problem with the right spare part.
At Boiler Spares Ltd, we stock genuine and compatible Worcester Bosch parts for every common fault. Below is a complete guide to Worcester fault codes, what they mean, and which part you need to fix them.
EA — Ignition Lockout
What it means: The boiler tried to ignite but failed after multiple attempts.
Common causes:
- Blocked or faulty ignition electrode
- Gas supply issue
- Blocked burner
- Faulty gas valve
How to fix it: Check the gas supply and reset the boiler. If the fault returns, the ignition electrode is the most likely culprit. We stock electrodes for all Greenstar and Si/RI models.
A1 — Low Water Pressure
What it means: System pressure has dropped below 0.6 bar.
Common causes:
- Leak in the heating system
- Faulty pressure sensor
- Recently bled radiators
How to fix it: Re-pressurise via the filling loop. If pressure keeps dropping, replace the pressure sensor or check for leaks.
CE — Fan Fault
What it means: The boiler fan is not running at the correct speed or has failed.
Common causes:
- Faulty fan motor
- Blocked flue
- PCB not sending power to the fan
How to fix it: Check the flue for blockages first. If clear, the fan or PCB may need replacing.
D1 — Sensor Fault (Overheating)
What it means: The boiler has overheated and shut down for safety.
Common causes:
- Faulty NTC thermistor
- Pump failure (water not circulating)
- Sludge or blockage in the system
How to fix it: Check the pump is running. If the pump is fine, replace the NTC thermistor or overheat thermostat.
F0 — Internal Error / PCB Fault
What it means: The boiler’s printed circuit board (PCB) has detected an internal fault.
Common causes:
- PCB failure
- Wiring issue
- Intermittent electrical fault
How to fix it: Try resetting the boiler. If the fault persists, the PCB will need replacing. This should only be done by a Gas Safe engineer.
F7 — Flame Loss
What it means: The boiler lit but lost the flame during operation.
Common causes:
- Dirty or worn flame sensor
- Electrode gap incorrect
- Condensate blockage
How to fix it: Clean the flame sensor and electrodes. If the fault continues, replace the ignition electrode kit.
C6 — Pump Fault / Running Dry
What it means: The pump is running but the boiler is not detecting water flow.
Common causes:
- Airlock in the system
- Pump failure
- Blocked heat exchanger
How to fix it: Bleed all radiators and re-pressurise. If the pump is hot but silent, replace the circulation pump. We stock Grundfos and compatible Worcester pumps.
E9 — Water Pressure Sensor Fault
What it means: The pressure sensor is giving an incorrect reading.
Common causes:
- Faulty pressure sensor
- Wiring fault
- PCB issue
How to fix it: Replace the pressure sensor. This is a common failure on older Greenstar models.
A8 — Water Pressure Too High
What it means: System pressure is above 2.7 bar.
Common causes:
- Overfilled system
- Faulty expansion vessel
- Pressure relief valve stuck open
How to fix it: Release pressure via a radiator bleed valve. If it keeps happening, replace the expansion vessel or safety valve.
E5 — Primary Flow Sensor Fault
What it means: The boiler can’t read the temperature of the water leaving the heat exchanger.
Common causes:
- Faulty NTC thermistor on the flow pipe
- Wiring issue
- Scale buildup on the sensor
How to fix it: Replace the flow thermistor. These are inexpensive and straightforward to fit.
Quick Reference Table
Table
| Fault Code | Meaning | Likely Part Needed |
| EA | Ignition lockout | Ignition electrode |
| A1 | Low pressure | Pressure sensor |
| CE | Fan fault | Fan or PCB |
| D1 | Overheating | Thermistor, pump, or thermostat |
| F0 | Internal error | PCB |
| F7 | Flame loss | Ignition electrode |
| C6 | Pump fault | Circulation pump |
| E9 | Pressure sensor fault | Pressure sensor |
| A8 | High pressure | Expansion vessel or safety valve |
| E5 | Flow sensor fault | Flow thermistor |
When to Call a Gas Safe Engineer
While many Worcester Bosch faults can be fixed with the right spare part, any work involving the gas valve, burner, or boiler casing must be carried out by a Gas Safe registered engineer. Always isolate the boiler and follow safe working practices.
Shop Worcester Bosch Boiler Spares
At Boiler Spares Ltd, we stock thousands of genuine and compatible Worcester Bosch parts — from ignition electrodes and pumps to, thermistors, and expansion vessels. Based in Huddersfield, we offer fast UK delivery so you can get your heating back on quickly.