Biasi ActivA 18S Fault codes & diagnostics

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

System Natural Gas 18 kW 2009 onwards Discontinued
GC Number 41-583-11

Replaced by: Advance Plus 7 System

Download the Biasi ActivA 18S 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 →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 13 High 1 Medium 1 Low
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
41-583-11 ActivA 18S 2009–present
Just want the most common Biasi ActivA 18S faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 16 documented codes

Tap any card for details

E01

Your boiler has failed to light, likely because the fuel supply is interrupted or the ignition system cannot spark safely.

High DIY-safe £120-£350

What to check first

  1. Check if your gas supply is turned on at the meter
  2. If you have a prepaid gas meter, ensure it has sufficient credit
  3. Press and hold the 'Reset' button for five seconds
  4. Check if other gas appliances in your home, like a hob, are working

Parts commonly replaced

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

Related codes

Full explanation for E01
Er

Your boiler has gone into a 'lockout' mode because it has detected a problem and has shut down as a safety precaution.

High DIY-safe £100-350

What to check first

  1. Locate the selector knob on the front of the boiler control panel.
  2. Turn the knob to the 'Reset' position and hold it for a few seconds.
  3. Return the knob to its original position and wait to see if the boiler restarts.

Parts commonly replaced

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

Related codes

Full explanation for Er
Er01

Your boiler has failed to light the flame, which means it cannot provide any heating or hot water for your home.

High DIY-safe £100-£350

What to check first

  1. Check if your gas supply is turned on and other gas appliances are working
  2. Press and hold the Reset button for 2 to 3 seconds.
  3. Ensure your pre-paid gas meter has credit, if applicable.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB (Control board)

Related codes

Full explanation for Er01
Er02

Your boiler has overheated, prompting a safety switch to shut the system down to prevent damage.

High DIY-safe £100-220

What to check first

  1. Allow the boiler to cool down for at least 20 minutes
  2. Check that your radiator valves are open and not blocked
  3. Turn the selector switch to the 'Reset' position for a few seconds and then back to 'ON'

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger (if scaled)

Related codes

Full explanation for Er02
Er03

Your boiler has detected a general internal error that is preventing it from running safely and requires a professional inspection.

High Engineer only £120-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring harness
  • Internal fuse

Related codes

Full explanation for Er03
Er04

Your boiler has detected that there is not enough water flowing through the system to operate safely.

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 low, use the filling loop underneath the boiler to top it up.
  3. Ensure all radiator valves and isolation valves are fully open.
  4. Reset the boiler by turning the selector switch to the 'R' position for a few seconds.

Parts commonly replaced

  • Circulating pump
  • Primary water pressure switch
  • Flow temperature sensor (NTC)

Related codes

Full explanation for Er04
Er05

Your boiler has stopped working because the fan that removes waste gases cannot be properly controlled or monitored by the system.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • Main PCB
  • Wiring harness

Related codes

Full explanation for Er05
Er06

Your boiler has stopped working because a sensor that monitors the water temperature for your radiators has likely failed.

High Engineer only £90-160

Parts commonly replaced

  • Central heating NTC temperature probe
  • Wiring harness

Related codes

Full explanation for Er06
Er07

Your boiler is having trouble measuring the temperature of your hot water, which means it cannot heat it correctly.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Temperature Probe (NTC)
  • Wiring harness

Related codes

Full explanation for Er07
Er08

Your boiler is having trouble communicating with an outdoor sensor used to monitor the weather, but it should still be able to provide heating and hot water.

Low DIY-safe £90-160

What to check first

  1. Check if an external temperature sensor is actually installed on an outside wall.
  2. Inspect the sensor for any obvious physical damage or loose wiring.
  3. Restart the boiler by turning the selector knob to the 'Reset' position for five seconds.

Parts commonly replaced

  • External Temperature Probe (NTC)
  • Wiring harness

Related codes

Full explanation for Er08
Er09

Your boiler has detected that a sensor monitoring the temperature of exhaust gases is not working correctly, causing the system to shut down for safety.

High Engineer only £120-£200

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Sensor Wiring Loom
  • Main Circuit Board (PCB)

Related codes

Full explanation for Er09
Er10

Your boiler has shut down because it has detected that the exhaust gases are becoming dangerously hot, which usually indicates a blockage or a heat exchange problem.

Emergency Engineer only £120-350

Parts commonly replaced

  • Flue NTC sensor
  • Primary Heat Exchanger
  • Main PCB

Related codes

Full explanation for Er10
Er11

Your boiler detects a flame when it shouldn't be there, causing the system to shut down safely until the issue is resolved.

High Engineer only £120-300

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Printed Circuit Board (PCB)
  • Gas valve

Related codes

Full explanation for Er11
Er14

Your boiler has detected that water isn't moving through the system properly, causing it to overheat and lock itself for protection.

High DIY-safe £180-450

What to check first

  1. Check the pressure gauge is between 1.0 and 1.5 bar; top up using the filling loop if it is too low.
  2. Ensure all radiator valves and internal isolation valves are fully open.
  3. Wait 15 minutes for the safety timer to expire and then press ‘Reset’.

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger
  • Primary Flow NTC Sensor

Related codes

Full explanation for Er14
Li01

Your boiler has shut down because it grew too hot while trying to heat your water, usually due to poor water flow through the system.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar
  3. Reset the boiler by turning the control knob to 'R' for five seconds

Parts commonly replaced

  • Diverter valve actuator
  • Secondary heat exchanger
  • NTC temperature sensor

Related codes

Full explanation for Li01
lock-out

Your boiler has switched itself off because it has detected that it is getting too hot or there is a problem with the exhaust gases.

High DIY-safe £120-250

What to check first

  1. Check that your radiator valves are open and not turned off.
  2. Ensure there are no blockages around the external flue pipe.
  3. Press the 'Reset' button on the front of the boiler control panel once.

Parts commonly replaced

  • Safety Thermostat (Overheat Stat)
  • Flue Temperature Probe
  • Central Heating Pump

Related codes

Full explanation for lock-out