Buderus 600-28C Fault codes & diagnostics

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

Combi Natural Gas 600 kW 2003 onwards Discontinued
GC Number 47-110-02

Replaced by: Worcester Bosch Greenstar 28i Junior

Download the Buderus 600-28C manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
15 High
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-110-02 Boulter Buderus 600-28C 2003–present
Just want the most common Buderus 600-28C faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 15 documented codes

Tap any card for details

2E

Your boiler has stopped working because the water pressure is too low for it to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) under or near the boiler.
  2. Open the one or two taps on the loop slowly until you hear water flowing.
  3. Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for 2E
3A

Your boiler has stopped working because the main control board is unable to talk to or control the fan.

High Engineer only £280-550

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 3A
3P

Your boiler has stopped working because the fan that clears exhaust gases is not spinning at the correct speed to keep the system safe.

High Engineer only £200-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Venturi tube

Related codes

Full explanation for 3P
3Y

Your boiler has detected that the internal fan is spinning at the wrong speed, which prevents the unit from safely starting the combustion process.

High Engineer only £200-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 3Y
4A

Your boiler has detected that the water inside is getting much too hot, so it has shut down to prevent damage.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Bleed all radiators to remove trapped air
  4. Press the reset button once the boiler has cooled down

Parts commonly replaced

  • Circulating pump
  • Flow temperature thermistor (NTC)
  • Main heat exchanger (de-scaling)

Related codes

Full explanation for 4A
4E

Your boiler's temperature sensors have detected an internal conflict or failure, meaning the system can no longer safely monitor how hot the water is getting.

High Engineer only £120-220

Parts commonly replaced

  • Dual NTC Temperature Sensor
  • Sensor Wiring Harness
  • Main Control Board (PCB)

Related codes

Full explanation for 4E
4P

Your boiler has lost communication with its internal temperature sensors, meaning it cannot monitor water heat safely and has shut down as a precaution.

High Engineer only £120-£240

Parts commonly replaced

  • Bi-sensor (Dual Temperature Sensor)
  • Wiring harness connectors

Related codes

Full explanation for 4P
4Y

Your boiler has detected that a safety temperature sensor has lost its connection or stopped working correctly.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness
  • Safety sensor (Bi-sensor)

Related codes

Full explanation for 4Y
6A

Your boiler is trying to light but cannot detect a flame, so it has shut down for safety.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances in your home (like a hob) are working to ensure gas supply.
  2. Verify that your external gas meter has credit if you use a prepay meter.
  3. Check that the white condensate pipe leaving the boiler isn't frozen if it is winter.
  4. Try resetting the boiler using the reset button on the front panel.

Parts commonly replaced

  • Ionisation Electrode
  • Ignition Lead
  • Gas Valve
  • Condensate Trap

Related codes

Full explanation for 6A
6C

Your boiler thinks there is a flame when there shouldn't be, or the sensor that detects the flame is sending a false signal, causing the system to shut down for safety.

High Engineer only £120-£280

Parts commonly replaced

  • Ionisation electrode
  • Flame sensor lead
  • Control PCB

Related codes

Full explanation for 6C
6P

Your boiler is struggling to ignite because the starting component is staying on longer than it should to try and get the flames going.

High Engineer only £140-£260

Parts commonly replaced

  • Glow igniter
  • Ionisation electrode
  • Gas valve

Related codes

Full explanation for 6P
8Y

Your boiler has paused because a safety switch related to your underfloor heating has detected a problem or has been disconnected.

High DIY-safe £60-140

What to check first

  1. Check if your underfloor heating thermostat is turned down too low or is turned off.
  2. Verify that the underfloor heating pump and manifold wiring centers have power.
  3. Ensure any manual safety limit thermostats on the underfloor pipework haven't been tripped by high temperatures.

Parts commonly replaced

  • Underfloor heating limit thermostat
  • Wiring centre relay
  • External fuse

Related codes

Full explanation for 8Y
CA

Your boiler has detected that the water returning to the unit is much too hot, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1 and 1.5 bar
  3. Restart the boiler to see if the error clears

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Circulation pump
  • Main heat exchanger (flushing)

Related codes

Full explanation for CA
CO

Your boiler has detected an issue with the sensor that monitors water pressure, preventing it from running safely.

High Engineer only £140-£250

Parts commonly replaced

  • Pressure sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for CO
E1

Your boiler's internal computer has encountered a critical error, meaning the system has safely shut down to prevent further damage.

High Engineer only £200-450

Parts commonly replaced

  • UBA Control Unit
  • Wiring harness

Related codes

Full explanation for E1
Status & diagnostic codes

1 operating states & engineer diagnostics

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

2L Diagnostic Your boiler is performing a routine check of its internal pump to ensure everything is working correctly before it starts up.