Worcester Bosch 28i RSF Fault codes & diagnostics

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

Combi Natural Gas 28 kW 1997-2005 Discontinued
GC Numbers 47-311-8647-311-8747-311-9047-311-91

Replaced by: Greenstar 28i Junior

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

This boiler uses indicator light combinations

Note which lights are on, off, or flashing and at what speed. Match the combination to the cards below. Do not reset until you have noted the pattern. How to read fault codes →

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

All 4 documented codes

Tap any card for details

LED / flash-pattern codes
Blue indicator light flashing

Your boiler is signalling a general internal fault that has caused it to stop working to ensure your safety.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Air Pressure Switch
  • Fan
Full explanation for Blue indicator light flashing
Digital codes
LOCKOUT

Your boiler has failed to light the flame after several attempts and has safely shut itself down to prevent a gas buildup.

High Engineer only £180-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for LOCKOUT
Off / Off

Your boiler has completely lost power and its display screen is blank, meaning it cannot operate or heat your home.

High DIY-safe £100-£450

What to check first

  1. Check if other appliances are working to rule out a general power cut
  2. Check your home's main consumer unit (fuse box) to see if a circuit has tripped
  3. Check the fused spur switch next to the boiler is turned on and the fuse inside hasn't blown

Parts commonly replaced

  • Internal PCB fuse
  • Printed Circuit Board (PCB)
  • External Fused Spur
Full explanation for Off / Off
On / Off

Your boiler is providing hot water as normal, but there is a communication issue preventing the heating from turning on when you use your thermostat.

Medium DIY-safe £60-250

What to check first

  1. Check that the batteries in your wall thermostat or room programmer haven't run out
  2. Ensure the heating timer is set to 'ON' or 'AUTO' and the thermostat is turned up higher than the current room temperature
  3. Check if any wireless receiver attached to the boiler has a power light or is showing a signal connection

Parts commonly replaced

  • Room Thermostat
  • Wireless Receiver
  • Diverter Valve Actuator
Full explanation for On / Off
Status & diagnostic codes

5 operating states & engineer diagnostics

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

Blue indicator light off Status Your boiler has no power and is completely switched off, meaning you have no heating or hot water until the electrical supply is restored. Blue light on Status Your boiler is operating exactly as it should and there is nothing to worry about. F2 1.25AT Diagnostic Your boiler has stopped working because an internal safety fuse has blown, cutting off the electrical power to the system's control board. Off (No light) Status Your boiler is not receiving electrical power or does not realise you are asking for heating or hot water. Steady on (Burner lit) Status Your boiler is working exactly as it should and is currently burning gas to provide heating or hot water.