Common problems guide

The most common Viessmann Vitodens 242-F B2UA problems

The faults most likely to send a Viessmann Vitodens 242-F B2UA 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.
55 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
A2 High DIY-safe

Your boiler has detected that the water pressure in the system has dropped too low to operate safely, causing it to shut down to prevent damage.

What to try first

Locate the internal or external filling loop (braided silver hose) usually found at the bottom of the unit.Open the filling valves slowly until you hear water moving and watch the pressure gauge rise to between 1.0 and 1.5 bar.Close both valves completely and press the reset button on the boiler control panel.

Est. cost
£0-120
Parts
Filling loop valve, Pressure sensor, Expansion vessel
Full guide for A2
02
A8 High DIY-safe

Your boiler has detected that water is struggling to flow through the system properly, which may be due to trapped air or a blockage.

What to try first

Check your boiler pressure gauge and top up the system to 1.5 bar if it is low.Bleed all radiators in your home starting from the bottom floor to ensure no air is trapped in the system.Restart the boiler using the reset button or power cycle it at the fused spur.

Est. cost
£120-250
Parts
Central heating pump, Flow sensor, Plate heat exchanger
Full guide for A8
03
E6 High DIY-safe

Your boiler has stopped working because the water pressure inside your heating system has dropped too low.

What to try first

Locate the external filling loop, usually two silver valves connected by a braided metal hose underneath the boiler.Open both valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves firmly once the correct pressure is reached and reset the boiler.

Est. cost
£80-150
Parts
Pressure relief valve, Expansion vessel, Pressure sensor
Full guide for E6
04
20 High Engineer

Your boiler has stopped working because it can no longer accurately measure the temperature of the water being sent to your radiators.

Est. cost
£120-220
Parts
Flow temperature sensor (NTC), Wiring harness connecting to the sensor
Full guide for 20
05
28 High Engineer

Your boiler has lost connection with its main internal temperature sensor, meaning it cannot accurately monitor the water temperature to heat your home.

Est. cost
£120-£200
Parts
System flow temperature sensor (NTC), Sensor wiring harness
Full guide for 28
06
30 High Engineer

Your boiler has detected a fault with the sensor that measures water temperature, causing the system to shut down for safety.

Est. cost
£140-£250
Parts
Boiler water temperature sensor (NTC), Sensor wiring harness
Full guide for 30
Parts most often replaced

on the Viessmann Vitodens 242-F B2UA

Filling loop valvePressure sensorExpansion vesselCentral heating pumpFlow sensorPlate heat exchanger

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 Viessmann 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 55-code list for the Viessmann Vitodens 242-F B2UA

Related guides

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