Biasi ActivA 18S Fault codes & diagnostics

12 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

The fault code is already on your display

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.
10 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

Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.

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 12 documented codes

Tap any card for details

E02

Your boiler has likely overheated, causing a safety switch to trip and shut down the system to prevent damage.

High DIY-safe £90-250 Shared across the range

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Wait for the boiler to cool down and press the 'Reset' button

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Thermistors (NTC sensors)

Related codes

Full explanation for E02
E03

Your boiler has detected that the exhaust gases are getting too hot or a safety fuse has tripped to prevent the unit from overheating.

High Engineer only £90-180 Shared across the range

Parts commonly replaced

  • Flue NTC probe
  • Thermal fuse
  • Heat exchanger cleaning

Related codes

Full explanation for E03
E04

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £60-120 Shared across the range

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.
  2. Open the black plastic valves slowly until you hear water entering the system.
  3. Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Water pressure switch
  • Expansion vessel
  • Filling loop valves

Related codes

Full explanation for E04
E05

Your boiler has stopped working because it cannot safely move air or waste gases through the system, usually due to a fan issue.

High Engineer only £180-350 Shared across the range

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Main PCB

Related codes

Full explanation for E05
E06

Your boiler has stopped working because it can no longer accurately measure the temperature of the water inside the system.

High Engineer only £90-160 Shared across the range

Parts commonly replaced

  • Central Heating (CH) NTC Temperature Sensor
  • Wiring Harness

Related codes

Full explanation for E06
E07

Your boiler's hot water sensor has malfunctioned or developed a wiring fault, meaning it cannot accurately measure the temperature of the water coming out of your taps.

Medium Engineer only £90-160 Shared across the range

Parts commonly replaced

  • DHW Temperature Probe (NTC)
  • Wiring Harness

Related codes

Full explanation for E07
E08

Your boiler is struggling to understand how cold it is outside, which can cause your heating to behave unpredictably or stop working efficiently.

Low Engineer only £90-160 Shared across the range

Parts commonly replaced

  • External temperature sensor
  • Sensor wiring harness

Related codes

Full explanation for E08
E09

Your boiler has detected that the exhaust gases are too hot or the sensor that monitors them has failed, causing the system to shut down for safety.

High Engineer only £90-180 Shared across the range

Parts commonly replaced

  • Flue NTC sensor
  • Main heat exchanger (de-scale)
  • Wiring harness

Related codes

Full explanation for E09
E10

Your boiler has detected that the exhaust gases are getting too hot, so it has shut down as a safety precaution to prevent damage.

High Engineer only £90-180 Shared across the range

Parts commonly replaced

  • Flue NTC sensor
  • Main Heat Exchanger cleaning
  • Wiring harness

Related codes

Full explanation for E10
E14

Your boiler is struggling to circulate water properly, which usually means the pump is stuck or there is a blockage in the pipes.

High Engineer only £180-£350 Shared across the range

Parts commonly replaced

  • Circulation Pump
  • Flow Switch
  • Main PCB

Related codes

Full explanation for E14
E15

Your boiler has stopped working because it cannot drain away the waste water it produces, or it is struggling to detect a flame.

High DIY-safe £90-180 Shared across the range

What to check first

  1. Check the white plastic pipe leading from the boiler to the outside for signs of freezing or blockages.
  2. If the external pipe is frozen, gently pour warm (not boiling) water over it to melt the ice.
  3. Reset the boiler using the control knob or reset button once the blockage is cleared.

Parts commonly replaced

  • Condensate trap
  • Flame sensing electrode
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E15
Er99

Your boiler has lost its internal memory or configuration settings and can no longer recognize what model it is.

High Engineer only £180-350 Shared across the range

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • PCB Configuration Key

Related codes

Full explanation for Er99