Biasi ActivA 25C Fault codes & diagnostics

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

Combi Natural Gas 2009-present
GC Number 47-583-21
Download the Biasi ActivA 25C manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
2 Emergency 13 High 1 Medium 1 Low
Fault codes

All 17 documented codes

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E01

Your boiler has failed to light the gas flame, meaning it has shut itself down for safety and cannot provide heating or hot water.

High DIY-safe £100-£350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Perform a reset by turning the control knob to 'R' for five seconds and then back to the on position.
  3. Verify that your condensate pipe (the plastic pipe leading outside) isn't frozen if it is currently winter.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E01
E23

Your boiler has stopped working because it cannot detect that the gas valve is opening correctly, meaning it is preventing itself from igniting for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Main PCB
  • Wiring harness

Related codes

Full explanation for E23
Er01

Your boiler has stopped working because it cannot light its internal flame, which means you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for Er01
Er02

Your boiler has detected that it is overheating and has automatically shut down to prevent damage or dangerous pressure buildup.

High Engineer only £150-250

Parts commonly replaced

  • Safety limit thermostat
  • NTC sensor
  • System filter
  • Heat exchanger

Related codes

Full explanation for Er02
Er03

Your boiler's internal computer has encountered a critical error and cannot safely operate the heating or hot water systems.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board
  • Wiring harness

Related codes

Full explanation for Er03
Er04

Your boiler has detected that the water pressure inside your heating system is too low to operate safely, or the water is not circulating correctly.

High DIY-safe £90-180

What to check first

  1. Check your external pressure gauge to confirm it reads below 1 bar.
  2. Locate the external filling loop (usually two silver valves with a flexible hose between them).
  3. Open the valves slowly to allow water into the system until the pressure gauge reaches 1.5 bar, then turn the valves off tightly.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Central heating pump

Related codes

Full explanation for Er04
Er05

Your boiler is struggling to clear exhaust fumes safely, so it has turned itself off to prevent carbon monoxide buildup.

High Engineer only £150-300

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Venturi

Related codes

Full explanation for Er05
Er06

Your boiler is unable to measure the water temperature correctly because one of its thermal sensors has likely failed or disconnected.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor

Related codes

Full explanation for Er06
Er07

Your boiler is struggling to accurately measure the temperature of your hot water, which means it has stopped providing hot water to prevent overheating.

Medium Engineer only £120-180

Parts commonly replaced

  • DHW NTC Sensor

Related codes

Full explanation for Er07
Er08

Your boiler is having trouble reading the outside temperature from a weather sensor, which may cause your heating system to run less efficiently.

Low Engineer only £90-160

Parts commonly replaced

  • External temperature sensor
  • Wiring loom

Related codes

Full explanation for Er08
Er09

Your boiler is struggling to clear exhaust gases properly, which has triggered a safety shut-off to prevent blockages or overheating in the flue system.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness
  • Flue seals

Related codes

Full explanation for Er09
Er10

Your boiler has detected that the temperature of the exhaust fumes passing through the flue is higher than it should be, causing the system to stop working as a safety precaution.

Emergency Engineer only £150-250

Parts commonly replaced

  • Flue gas NTC sensor
  • Wiring harness
  • PCB

Related codes

Full explanation for Er10
Er11

Your boiler is detecting a false flame signal when it shouldn't be burning, which prevents it from safely starting up.

High Engineer only £150-300

Parts commonly replaced

  • Flame sensor electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Er11
Er14

Your boiler has detected that the water is not circulating properly through the main heating system, likely due to a blockage or a pump failure.

High Engineer only £150-350

Parts commonly replaced

  • Circulation pump
  • Pressure sensor
  • Heat exchanger

Related codes

Full explanation for Er14
Er14+RESET

Your boiler has stopped working because it has detected a lack of water flow or the water inside has become dangerously hot.

High Engineer only £150-350

Parts commonly replaced

  • Water pump
  • Flow switch
  • High limit thermostat
  • PCB

Related codes

Full explanation for Er14+RESET
Er99

Your boiler has lost its configuration settings or isn't receiving power correctly, meaning it doesn't know which specific model it is supposed to be.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Panel Interface

Related codes

Full explanation for Er99
Li01

Your boiler has shut down because the internal water temperature has become too hot while trying to provide hot water.

High DIY-safe £100-280

What to check first

  1. Check that the radiator valves and the main boiler valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Reset the boiler using the control knob to see if the fault clears

Parts commonly replaced

  • DHW Temperature Sensor (NTC)
  • Plate Heat Exchanger
  • Circulation Pump

Related codes

Full explanation for Li01
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