Common problems guide

The most common Biasi ActivA 18S problems

The faults most likely to send a Biasi ActivA 18S into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
12 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
E02 High DIY-safe

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

What to try first

Check that all radiator valves are fully open to allow water to circulateEnsure your boiler pressure is between 1.0 and 1.5 bar on the gaugeWait for the boiler to cool down and press the 'Reset' button

Est. cost
£90-250
Parts
Overheat Thermostat, Circulation Pump, Thermistors (NTC sensors)
Full guide for E02
02
E04 High DIY-safe

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

What to try first

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

Est. cost
£60-120
Parts
Water pressure switch, Expansion vessel, Filling loop valves
Full guide for E04
03
E15 High DIY-safe

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

What to try first

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

Est. cost
£90-180
Parts
Condensate trap, Flame sensing electrode, Printed Circuit Board (PCB)
Full guide for E15
04
E03 High Engineer

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

Est. cost
£90-180
Parts
Flue NTC probe, Thermal fuse, Heat exchanger cleaning
Full guide for E03
05
E05 High Engineer

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

Est. cost
£180-350
Parts
Fan assembly, Air pressure switch, Main PCB
Full guide for E05
06
E06 High Engineer

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

Est. cost
£90-160
Parts
Central Heating (CH) NTC Temperature Sensor, Wiring Harness
Full guide for E06
Parts most often replaced

on the Biasi ActivA 18S

Overheat ThermostatCirculation PumpThermistors (NTC sensors)Water pressure switchExpansion vesselFilling loop valves

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Biasi shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 12-code list for the Biasi ActivA 18S

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →