Common problems guide

The most common Biasi Concept 400 20 1 Mfs problems

The faults most likely to send a Biasi Concept 400 20 1 Mfs 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.
38 documented codes
6 most common
4 DIY-safe checks
2 engineer needed

The 6 most common faults

01
Er04 High DIY-safe

Your boiler has detected that the water pressure inside your heating system is too low to operate safely and effectively.

What to try first

Locate the filling loop, which is a silver braided hose under your boiler.Open the small valve or tap attached to the hose until you hear water flowing.Watch the pressure gauge on the front of the boiler until the needle reaches between 1.0 and 1.5 bar.Close the valve tightly to stop the flow.

Est. cost
£80-150
Parts
Filling loop, Pressure sensor, Expansion vessel
Full guide for Er04
02
Er04+ High DIY-safe

Your boiler has detected that there is either not enough water inside the system or that the water is not circulating correctly, which prevents it from heating your home.

What to try first

Check your boiler pressure gauge; if it is below 1 bar, locate the filling loop under the boiler.Open the valves to allow water into the system until the gauge reaches 1.5 bar, then turn the valves off securely.Restart your boiler to see if the error clears.

Est. cost
£100-250
Parts
Central heating pump, Pressure sensor, Flow switch
Full guide for Er04+
03
04E High DIY-safe

Your boiler has detected that water is not circulating correctly through the system, which is preventing it from heating your home or water safely.

What to try first

Check the pressure gauge on the front of the boiler; if it is below 1 bar, locate the filling loop under the boiler.Open the filling loop valves to top up the system pressure until the gauge reads between 1 and 1.5 bar.Close the valves tightly and restart the boiler.

Est. cost
£120-250
Parts
Circulation pump, Flow switch, Pressure sensor
Full guide for 04E
04
18E 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 the boiler pressure gauge on the front display; if it is below 1 bar, your system needs re-pressurizing.Locate the external filling loop (usually two silver taps connected by a flexible hose underneath the boiler).Slowly open the taps to allow water into the system until the gauge reaches 1.5 bar, then turn both taps off tightly.

Est. cost
£80-150
Parts
Central heating pump, Flow switch, Pressure sensor
Full guide for 18E
05
Er01 High Engineer

Your boiler has stopped working because it cannot light the flame required to produce heat or hot water.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, Condensate trap
Full guide for Er01
06
Er02 High Engineer

Your boiler has switched itself off because it has detected an overheating issue, which prevents it from operating until the fault is corrected.

Est. cost
£150-300
Parts
Safety limit thermostat, Primary heat exchanger, Pump (if causing circulation issues)
Full guide for Er02
Parts most often replaced

on the Biasi Concept 400 20 1 Mfs

Filling loopPressure sensorExpansion vesselCentral heating pumpFlow switchCirculation 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
See the full 38-code list for the Biasi Concept 400 20 1 Mfs

Related guides

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