Medium
F4 on Heatline Capriz 24

Your boiler is struggling to detect the temperature of the water being heated for your taps, which means it will likely stop providing hot water until the faulty sensor is replaced.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Domestic Hot Water (DHW) sensor fault

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related fault codes

F5View →

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

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 →