Boiler Fault Guide
Worcester Bosch Boiler Fault Codes: EA, E9, D5, 227 and More
Worcester Bosch boiler fault codes describe conditions detected by a particular boiler or control; match the full display and model to its manual before choosing a safe check or arranging diagnosis. If you smell gas: leave, call the National Gas Emergency Service on 0800 111 999.
This guide covers domestic natural-gas boilers, with model-specific examples below. A code does not establish which component has failed. Start with boiler fault codes explained for the wider meaning of display messages.
Call with your postcode, the boiler make and any fault code showing.
- Gas Safe registered: 648977
- Phone line open 24/7
- Same-day appointments available
Before Checking a Code: Gas Smells, CO Alarms and Unsafe Boilers
Stop troubleshooting if you smell gas, hear a CO alarm or suspect carbon monoxide exposure.
- Gas smell: avoid flames and electrical switches. Open doors or windows and turn off gas at the meter only if safe, without delaying leaving. Call 0800 111 999 from a safe place.
- CO alarm or suspected exposure: get outside into fresh air. For suspected symptoms, contact NHS 111, or 999 if serious, without delaying medical help for a gas call. Report an alarm to the gas emergency service. Carbon monoxide has no smell.
Do not re-enter until advised. Never open the boiler casing, work on gas components or bypass safety devices. A fault code cannot establish that an appliance is safe.
Identify the Worcester Model and Record the Whole Display
Record the full model, every displayed character and whether the message appears on the boiler or a separate control.
Find the model
use appliance paperwork or an externally accessible label.
Identify the control
record its model separately.
Photograph the display
capture alternating screens, numbers and written messages.
Match the instructions
check the full model and applicable manual edition.
For example, the Greenstar i System user instructions show EA with accompanying number 227: record both. “30CDi” alone may not identify the correct manual. Never remove casing to find identification details.
Worcester Boiler Fault Codes at a Glance: Match the Model First
Use the entry matching your model and complete display; similar-looking codes can describe different conditions.
These are selected examples, not a complete list. Record the display and consult the matched owner instructions. Internal investigation belongs to an engineer; none of these conditions proves a particular part needs replacement.
Verify: check against the manufacturer's manual
Persistent faults need assessment; see Worcester Bosch boiler repairs.
EA/227, Greenstar Si Compact ErP
expected flame signal not established after ignition. Source: Worcester manual 6720813278, fault table.
EA/229, Greenstar Si Compact ErP
flame-detection signal lost during operation. Source: 6720813278, fault table.
E9/224, Greenstar Si Compact ErP
temperature-limiter condition. Source: 6720813278, fault table.
Fd, Greenstar CDi Classic System
unintended reset. Source: 6720815727, Table 5.
Fd/231, Greenstar i System
power interruption during lockout. Source: 6720806945, section 8.1.2.
A21, Comfort I RF control
radio-link problem. Source: 6720810964, 2017/02, sections 6–7.
A21/1001, Sense I control
configuration issue. Source: 6720648748, section 6.2.
A28, Comfort I RF control
pairing-state message within this control’s instructions. Source: 6720810964, sections 6–7.
D5, Greenstar FS 30CDi/FS 42CDi Regular
condensate-overflow condition. Source: 8716115216c, page 49.
C6, Greenstar CDi Classic System
fan-speed condition requiring professional assessment. Source: 6720815727, Table 5.
F7, Greenstar CDi Classic System
flame detected while the appliance is off. Source: 6720815727, Table 5.
F7/228, Greenstar Si Compact ErP
flame signal detected before startup. Source: 6720813278, fault table.
Worcester Boiler Fault 227 and EA: What Does the Display Mean?
On the Greenstar Si Compact ErP covered by manual 6720813278, EA/227 means the expected flame signal was not established after ignition.
Condition
the boiler has not detected the expected ionisation, or flame-detection, signal.
Possible causes
supply, ignition and flame-sensing problems need distinguishing.
Diagnosis
the code alone cannot identify a faulty gas valve, electrode or condensate blockage.
Do not transfer this meaning to a Greenstar 4000 from the number alone. Follow its own manual. Gas-pressure testing, electrode cleaning and gas-valve checks are engineer work.
Worcester Fd Codes: Why Fd and Fd 231 Need Different Lookups
Fd differs by range: the CDi Classic System manual describes an unintended reset, while the i System manual describes Fd/231 following power interruption during lockout.
- CDi Classic System, Fd: note whether a reset was pressed accidentally.
- i System, Fd/231: note any earlier code and whether power was interrupted.
The earlier fault may still need investigation. Preserve photographs and the sequence of events; leave fault-history retrieval to the engineer. Repeated resetting or power cycling does not establish that the cause has cleared.
E9 and 224 on a Worcester Boiler: Read the Accompanying Number
E9 needs the model and accompanying number because the Si Compact ErP manual lists distinct temperature-limit and sensor-circuit conditions.
Its E9/224 entry is a temperature-limiter example. That reports a safety condition, rather than proving low pressure, pump failure or sludge. Other E9 entries require their own lookup; standalone 224 on another range also needs separate confirmation.
Record the full display. Do not manipulate pumps, test sensors, vent internal components or bypass a limiter. A persistent fault needs professional assessment.
A21 on Worcester Controls: Check Which Controller Shows It
A21 depends on the controller: Comfort I RF documentation identifies a radio-link problem, while Sense I lists a configuration issue for A21/1001.
The wireless Comfort I and wired Sense I therefore need different lookups. Comfort I’s A28 message also needs interpreting within its documented pairing context.
Check user-replaceable batteries and portable thermostat positioning only where the owner instructions permit. Do not unpair the control as a general remedy. Wiring, installer settings and component replacement belong to an engineer.
D5 on a Worcester Boiler: Why It Does Not Prove a Frozen Pipe
D5 on the natural-gas Greenstar FS 30CDi and FS 42CDi Regular reports condensate overflow, not proof that an external pipe is frozen.
Collection, pumping or discharge problems need distinguishing. Cold weather is useful context, but cannot identify the cause.
Observe only safely accessible external pipework. Any permitted thawing must use warm, never boiling, water from ground level. Do not use flames, climb ladders, dismantle pipework or access an internal condensate pump or trap.
What Can You Safely Check Before Calling?
Without gas, CO or other warning signs, check only normal user controls and indications described in your instructions.
Check Pressure Against Your Boiler’s Own Instructions
Read the accessible gauge or normal display and compare it with your model’s cold-system instructions; see boiler pressure and safe topping-up.
- Check the reading before assuming water is needed.
- Add water only using the identified filling arrangement and owner procedure.
- Stop if the arrangement is uncertain, pressure repeatedly falls or a leak is visible.
Reset Once Only If the Matched User Manual Allows It
Attempt one reset only if your exact user manual permits it and there are no unsafe-appliance warning signs.
- Record: photograph the original display.
- Check: confirm the permitted user procedure.
- Reset: follow that procedure once.
- Stop: arrange assessment if the fault remains or returns.
There is no universal button sequence or hold time.
- Note whether you have no heating or no hot water, or both.
- Observe the normal power indication and any supplier-reported interruption or meter message.
- Check thermostat demand, schedule and user-replaceable batteries.
- Record unusual sounds or visible leaks without opening anything.
Do not light another appliance to test the gas supply or touch meter equipment, wiring or receiver terminals.
When to Stop Checking and Call a Gas Safe Engineer
Arrange professional diagnosis when a fault persists, returns after one permitted reset or requires internal access.
Stop when:
- The boiler remains locked out.
- A fault returns after resetting.
- Pressure repeatedly falls.
- Water is leaking.
- The manual directs you to an engineer.
Reading a display is different from testing combustion, flame sensing, electrical circuits or gas components. Keep photographs, model details and the sequence of events for professional boiler fault finding and diagnosis. Gas or CO warning signs require the emergency action above before booking.
Boiler repair, servicing and gas work
Arrange Help for a Worcester Boiler Fault in London
Call us 24 hours a day, 7 days a week to discuss a Worcester boiler fault in London.
All Service 4 U’s Gas Safe registered engineers can assess the cause. Our business registration is 648977. Have your full model, complete display, affected function, postcode and attempted checks ready.
Discuss My Worcester Boiler Fault: 020 3740 6785
020 3740 6785
Frequently Asked Questions
What Does EA 229 Mean on a Worcester Boiler?
On the Greenstar Si Compact ErP covered by manual 6720813278, EA/229 reports loss of the flame-detection signal during operation. EA/227 concerns establishing that signal after ignition. Neither identifies the cause by itself. Record the complete display and follow the matched owner instructions or arrange diagnosis.
What Is a Code Plug on a Worcester Boiler?
A code plug is an internal control component, distinct from the fault code displayed on the screen. Its exact role depends on the model’s documentation. A message referring to it does not automatically prove PCB failure. Leave access, testing, configuration and replacement to an engineer.
Why Is the Blue Light Flashing, or the Display Showing a Symbol Instead of a Code?
A flashing light or unfamiliar symbol needs interpreting through the exact model’s display guide. The i System user instructions associate its flashing blue fault light with an alert. Record the colour and pattern, any alternating text, and what the boiler was doing. Do not apply that interpretation across every range.
Where Can I Find the Correct Worcester Fault-Code Manual or PDF?
Use Worcester Bosch’s official manual library and match the full model, manufacturing period and document edition. Your appliance paperwork can help resolve uncertainty. Operating instructions contain owner guidance; installation and servicing manuals contain engineer procedures. Finding a procedure in an engineer manual does not make it a homeowner task.
Is U9 the Same as 9U on a Worcester Display?
Do not assume U9 and 9U are interchangeable. Photograph the display and compare the character order with your model’s manual, including any accompanying number. Search-result spellings cannot confirm a manufacturer code. If the display remains unclear, pass the photograph and model details to an engineer without attempting internal checks.
Does My Worcester Boiler Have a Pilot Light I Can Relight?
Check your model’s operating instructions before assuming it has a standing pilot. A missing flame indication is not an instruction to relight anything. Record any ignition-related display and use the model-specific guidance above. Never use matches or a lighter, remove the casing or touch gas components to attempt relighting.
Still have a question or need urgent assistance? Call 020 3740 6785, tell us what has happened and we will tell you what happens next.