Medium Warning
A7 on Worcester Bosch Greenstar CDi Compact

Your boiler has lost the ability to measure the temperature of your hot water properly, which usually means your taps will only run stone cold or may fluctuate wildly in temperature.

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

Hot water NTC sensor defective

What causes this fault?

This fault occurs when the sensor responsible for monitoring your hot water temperature fails to send a reliable signal to the boiler's main control board. The most common reason is that the internal component of the sensor has degraded over time or suffered a short circuit, preventing the boiler from knowing how hot to heat your water. In some cases, the issue is caused by loose or corroded electrical connections between the sensor and the boiler.

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

A8View →B1View →E9View →

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →