Common problems guide

The most common Biasi Advance 25C problems

The faults most likely to send a Biasi Advance 25C into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

34 documented codes
6 most common
6 DIY-safe checks
0 engineer needed

The 6 most common faults

01
Er 01 High DIY-safe

Your boiler has tried to light several times but failed, so it has shut itself down for safety.

What to try first

Check if other gas appliances, like your hob, are working to ensure fuel is reaching the houseEnsure your gas meter hasn't run out of credit or been turned offPress and hold the 'Reset' button for five seconds to see if the boiler restarts

Est. cost
£100-280
Parts
Ignition electrode, Gas valve, Flame sensing probe
Full guide for Er 01
02
Er 02 High DIY-safe

Your boiler has switched itself off because it has detected that the water inside has become or is becoming too hot.

What to try first

Ensure all radiator valves are fully open to allow water to circulateCheck that the boiler pressure is between 1.0 and 1.5 bar on the gaugePress and hold the 'Reset' button for five seconds to restart the system

Est. cost
£100-280
Parts
Overheat Thermostat, Central Heating Pump, Main Heat Exchanger
Full guide for Er 02
03
Er 04 High DIY-safe

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

What to try first

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

Est. cost
£100-280
Parts
Circulating Pump, Water Pressure Switch, Flow Temperature Sensor
Full guide for Er 04
04
Er 14 High DIY-safe

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

What to try first

Check the pressure gauge and top it up to 1.5 bar if it is lowEnsure all radiator valves and isolation valves under the boiler are fully openCheck for any visible leaks around the pipework or radiators

Est. cost
£120-£350
Parts
Circulation Pump, Primary Thermistor (NTC Sensor), Flow Switch
Full guide for Er 14
05
An 11 High DIY-safe

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

What to try first

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

Est. cost
£90-280
Parts
Ignition Electrode, Flame Sensing Probe, Gas Valve
Full guide for An 11
06
Er 13 High DIY-safe

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

What to try first

Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barGently bleed air from your radiators using a radiator key

Est. cost
£120-£350
Parts
Circulation Pump, Main Heat Exchanger, Return Temperature Sensor
Full guide for Er 13

on the Biasi Advance 25C

Ignition electrodeGas valveFlame sensing probePrinted Circuit Board (PCB)Overheat ThermostatCentral Heating Pump

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

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See the full 34-code list for the Biasi Advance 25C