Worcester Bosch Junior 28i Fault codes & diagnostics

5 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 28 kW 2006-2010 Discontinued

Replaced by: Greenstar 28i Junior

Download the Worcester Bosch Junior 28i manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Just want the most common Worcester Bosch Junior 28i faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 5 documented codes

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265

Your boiler is temporarily limiting its power output because it is producing more heat than your radiators or taps can currently take away.

Low DIY-safe £0-120

What to check first

  1. Ensure all radiator valves (TRVs) are fully open to allow heat to circulate.
  2. Check that the boiler pressure is between 1 and 1.5 bar on the pressure gauge.
  3. Deep-clean any magnetic system filters if you are familiar with the process.

Parts commonly replaced

  • None (often a system settings issue)
  • Central heating pump
  • System filter

Related codes

Full explanation for 265
A1

Your boiler has detected that it is running without enough water inside, which is often caused by a leak or a pump that has jammed or failed.

High DIY-safe £180-350

What to check first

  1. Check the pressure gauge on the boiler and top it up to 1.5 bar using the filling loop
  2. Inspect visible pipework and radiators for any signs of water leaks
  3. Reset the boiler to see if the error clears after repressurising

Parts commonly replaced

  • Central heating pump
  • Pump capacitor
  • Automatic air vent

Related codes

Full explanation for A1
A8

Your boiler has lost its connection to your external room thermostat or heating controls, meaning it doesn't know when to turn on or off.

High Engineer only £90-180

Parts commonly replaced

  • RF Receiver
  • Internal Wiring Harness
  • External Room Thermostat

Related codes

Full explanation for A8
F1

Your boiler has stopped working because an internal safety fuse has failed, cutting off power to the system's control board.

High Engineer only £120-220

Parts commonly replaced

  • Internal PCB fuse
  • Main Control PCB

Related codes

Full explanation for F1
F2

Your boiler has stopped working because an internal electrical fuse has blown, cutting off the power needed for it to operate.

High Engineer only £120-200

Parts commonly replaced

  • Control board fuse
  • Main printed circuit board (PCB)

Related codes

Full explanation for F2
Status & diagnostic codes

9 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

24i Status This code is not actually an error; it is a status indicator showing the boiler is performing a routine performance check ten minutes after ignition. 28i Status This code is not actually an error; it is simply a status display showing the boiler's factory settings and performance rating during its initial startup phase. 200 Status Your boiler is working correctly and is simply indicating that it is currently busy heating your radiators. 203 Status Your boiler is currently in standby mode and is working correctly, simply waiting for you to turn on your heating or hot water. 208 Diagnostic Your boiler has been manually set to a testing mode used by engineers to check emissions and is not currently operating in its normal heating mode. Light on Status Your boiler is operating normally and is currently providing heat to your radiators. rE Status Your boiler is undergoing a restart process, which is often a temporary reaction to a minor internal fault or a manual reset action. T1 Diagnostic Your boiler is currently testing its ability to create a spark to light the burner. T3 Diagnostic Your boiler is checking if the internal pump is moving water correctly and has detected it might be stuck or failing.