Biasi Advance 25S Fault codes & diagnostics

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

Natural Gas 2017-present
GC Number 41-583-33
Download the Biasi Advance 25S 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.
22 High 4 Medium 2 Low
Just want the most common Biasi Advance 25S faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 28 documented codes

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An 11

Your boiler is struggling to light its burner or cannot detect that a flame has been successfully lit, preventing it from heating your water.

High DIY-safe £90-280

What to check first

  1. Check if other gas appliances, like your hob, are working to ensure gas is reaching the property.
  2. Verify that your prepaid gas meter has credit if applicable.
  3. Press and hold the 'Reset' button for five seconds to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Probe
  • Gas Valve

Related codes

Full explanation for An 11
Er 01

Your boiler has temporarily stopped working for safety reasons and needs to be manually reset to get it going again.

High DIY-safe £100-250

What to check first

  1. Locate the reset button on your boiler's control panel.
  2. Press and hold the reset button for approximately 3 to 5 seconds.
  3. Wait to see if the boiler fires up normally; if the error returns, do not keep resetting it.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Er 01
Er 02

Your boiler has temporarily stopped working for safety reasons and needs to be reset.

High DIY-safe £90-200

What to check first

  1. Locate the reset button or turn the mode selector switch to the reset position.
  2. Hold the reset button for 2 to 5 seconds and release it.
  3. Wait to see if the boiler fires up normally; do not repeat this more than three times.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Er 02
Er 03

Your boiler has temporarily stopped working as a safety precaution and needs to be reset.

High DIY-safe £90-250

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Biasi Advance 25C.
  2. Press and hold the reset button for approximately 3 to 5 seconds.
  3. Wait to see if the boiler fires up normally; if the code returns, do not keep resetting it.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for Er 03
Er 04

Your boiler has temporarily stopped working as a safety precaution to prevent potential damage.

High DIY-safe £100-250

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Biasi boiler.
  2. Hold the reset button down for about 2 to 5 seconds and release it.
  3. Wait a moment to see if the boiler fires up normally; if the error returns immediately, do not keep resetting it.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for Er 04
Er 04 +

Your boiler has detected that there is either not enough water in the system or the water isn't moving through the pipes correctly.

High DIY-safe £100-280

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. If the pressure is too low, use the filling loop underneath the boiler to top it up with water.
  3. Ensure all radiator valves and isolation valves under the boiler are fully open.

Parts commonly replaced

  • Circulating Pump
  • Water Pressure Switch
  • Flow Temperature Sensor

Related codes

Full explanation for Er 04 +
Er 05

Your boiler has safely shut itself down due to a general safety lock-out, meaning it has stopped working until the underlying issue is resolved.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for Er 05
Er 05 +

Your boiler has detected an issue with the internal air circulation system, which is preventing it from igniting safely.

High Engineer only £180-300

Parts commonly replaced

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

Related codes

Full explanation for Er 05 +
Er 06

Your boiler has temporarily stopped working for safety reasons and needs to be reset.

High DIY-safe £100-£250

What to check first

  1. Locate the reset button on your boiler control panel.
  2. Press and hold the reset button for about 5 seconds.
  3. Wait to see if the boiler fires up normally; do not repeat this more than twice.

Parts commonly replaced

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

Related codes

Full explanation for Er 06
Er 06 +

Your boiler is struggling to accurately measure its own internal water temperature, so it has shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • Central Heating NTC Sensor

Related codes

Full explanation for Er 06 +
Showing 11–20 of 28
Er 07

Your boiler has temporarily shut itself down for safety reasons and stopped providing heating and hot water.

High Engineer only £90-250

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Ignition electrode

Related codes

Full explanation for Er 07
Er 07 +

Your boiler is struggling to accurately measure the temperature of the hot water it provides, which has caused it to stop heating your water to prevent overheating.

Medium Engineer only £120-180

Parts commonly replaced

  • DHW NTC thermistor sensor

Related codes

Full explanation for Er 07 +
Er 08

Your boiler has safely shut itself down due to a recurring internal safety lock-out.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Electrode assembly
  • Gas valve

Related codes

Full explanation for Er 08
Er 08 +

Your boiler is struggling because it has lost the signal from an outdoor thermometer that helps it adjust your heating based on the weather.

Medium Engineer only £120-220

Parts commonly replaced

  • External NTC temperature sensor
  • Wiring harness

Related codes

Full explanation for Er 08 +
Er 09

Your boiler has safely shut itself down due to a general lockout fault that requires a professional engineer to diagnose and reset.

High Engineer only £100-250

Parts commonly replaced

  • Main PCB
  • Ignition Lead
  • Gas Valve

Related codes

Full explanation for Er 09
Er 09 +

Your boiler has detected an issue with the sensor that monitors the exhaust gas temperature, causing it to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flue gas NTC sensor
  • Wiring harness

Related codes

Full explanation for Er 09 +
Er 10

Your boiler has safely shut down and locked itself to prevent potential risks, meaning you currently have no heating or hot water.

High Engineer only £150-300

Parts commonly replaced

  • PCB
  • Gas valve
  • Ignition electrode

Related codes

Full explanation for Er 10
Er 12

Your boiler has sensed a problem with the internal sensor that monitors the temperature of the water returning from your radiators.

Medium Engineer only £90-160

Parts commonly replaced

  • Central heating return NTC thermistor
  • Wiring harness

Related codes

Full explanation for Er 12
Er 12 +

Your boiler has sensed a problem with the internal sensor that monitors the temperature of the water returning from your radiators.

Medium Engineer only £90-160

Parts commonly replaced

  • Central heating return NTC thermistor
  • Wiring harness

Related codes

Full explanation for Er 12 +
Er 13

Your boiler has detected that the water is getting too hot too quickly because it isn't circulating through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Gently bleed air from your radiators using a radiator key

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Return Temperature Sensor

Related codes

Full explanation for Er 13
Showing 21–28 of 28
Er 13 +

Your boiler has detected that the water is getting too hot too quickly because it isn't circulating through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Gently bleed air from your radiators using a radiator key

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Return Temperature Sensor

Related codes

Full explanation for Er 13 +
Er 14

Your boiler has safely shut itself down due to a safety lock-out, meaning it needs to be manually reset or checked by a professional before it will work again.

High DIY-safe £90-250

What to check first

  1. Locate the reset button or dial on your Biasi boiler control panel.
  2. Press and hold the reset button for about 3 to 5 seconds.
  3. Wait to see if the boiler fires up normally; if the code returns, do not keep resetting it.

Parts commonly replaced

  • PCB
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for Er 14
Er 14 +

Your boiler has detected that water is not flowing properly through the system fast enough, so it has safely shut down to prevent overheating.

High Engineer only £150-350

Parts commonly replaced

  • Circulating pump
  • Flow sensor
  • Automatic bypass valve

Related codes

Full explanation for Er 14 +
Er 19

Your boiler is having trouble measuring the temperature of the cold water coming in, which may affect how well it heats your hot water.

Low Engineer only £90-160

Parts commonly replaced

  • DHW inlet temperature probe
  • Connecting wiring harness

Related codes

Full explanation for Er 19
Er 19 +

Your boiler is having trouble measuring the temperature of the cold water coming in, which may affect how well it heats your hot water.

Low Engineer only £90-160

Parts commonly replaced

  • DHW inlet temperature probe
  • Connecting wiring harness

Related codes

Full explanation for Er 19 +
Er 25

Your boiler has temporarily stopped working for safety reasons and needs a professional to investigate the underlying cause.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for Er 25
Er 69

Your boiler has shut down because it has detected an electrical connection issue or an internal wiring conflict within its control system.

High Engineer only £100-£250

Parts commonly replaced

  • Main PCB
  • Wiring harness
  • External sensor

Related codes

Full explanation for Er 69
Li 01

Your boiler has completely stopped working and locked itself out as a safety precaution.

High Engineer only £100-250

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • PCB

Related codes

Full explanation for Li 01
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