High
F.42 on Vaillant ecoTEC exclusive

Your boiler has lost the digital instructions telling it which type of gas it should be using, causing it to stop working for your safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Fault:Codingresistor Gasfamilycodingresistorshortcircuit/interruption(onthePCB) – Gasfamilycodingresistormissing – Thecodingresistordoesnotmatchthegastypeselectionunder D.087 Incorrectcodingresistororincorrectgastypeselected

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →