Common problems guide

The most common Biasi Activ A problems

The faults most likely to send a Biasi Activ A 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.
31 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
03E High DIY-safe

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

What to try first

Check your boiler's pressure gauge on the front panel; it should be between 1 and 1.5 bar.If the pressure is below 1 bar, locate the filling loop (usually a silver braided hose under the boiler).Open the valves to allow water into the system until the gauge reaches 1.5 bar, then securely close the valves.

Est. cost
£90-180
Parts
Central heating pump, Pressure sensor, Flow switch
Full guide for 03E
02
18E High DIY-safe

Your boiler has detected that there is not enough water circulating inside the system to heat your home or provide hot water safely.

What to try first

Check your boiler's pressure gauge on the front panel; if it is below 1.0 bar, your system needs to be repressurised.Locate the filling loop (a silver flexible hose) underneath the boiler and open the valves to let water in until the needle reaches 1.5 bar.Close the filling loop valves tightly and check for any visible leaks around the radiators or pipes.

Est. cost
£90-180
Parts
Central heating pump, Flow switch, Pressure sensor
Full guide for 18E
03
Er 12 High Engineer

Your boiler has stopped working because a sensor that measures the temperature of the water returning to the system is failing to send a signal, causing the boiler to shut down as a precaution.

Est. cost
£120-200
Parts
Return NTC thermistor
Full guide for Er 12
04
04E High Engineer

Your boiler has detected an issue with the internal ventilation system that removes exhaust gases, and it has safely shut itself off to prevent unsafe operation.

Est. cost
£150-300
Parts
Fan assembly, Air pressure switch, PCB
Full guide for 04E
05
05E High Engineer

Your boiler has stopped heating because a temperature sensor is sending incorrect information, meaning the system doesn't know when the water is hot enough.

Est. cost
£120-200
Parts
Central Heating NTC Temperature Sensor
Full guide for 05E
06
09E High Engineer

Your boiler has detected that a sensor responsible for monitoring the temperature of the gases leaving your flue is not providing a correct reading, so it has shut down to ensure safety.

Est. cost
£120-220
Parts
Flue gas NTC sensor, Wiring harness
Full guide for 09E
Parts most often replaced

on the Biasi Activ A

Central heating pumpPressure sensorFlow switchReturn NTC thermistorFan assemblyAir pressure switch

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 31-code list for the Biasi Activ A

Related guides

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