Worcester Bosch Boiler A7 Error Code

Hot water temperature sensor fault on Worcester Bosch boilers.

Worcester Bosch All Worcester Bosch boiler codes

May need a pro

The NTC thermistor that measures domestic hot water has failed or lost its connection. A corroded or damaged plug, the sensor or the PCB are behind it. The boiler keeps working, but hot water temperature control gets less accurate.

Compatible models

Greenstar CDi Classic ErP combis and HighFlow 440CDi and 550CDi ErP boilers, per their user instructions and the CDi engineer's booklet.

Also shown as

No other codes are listed for this fault.

Difficulty

Try the basic checks, but the usual fix is a technician's job.

How to fix
When to call a pro
Parts
FAQ

Not sure you are reading the code right? See how to read Worcester Bosch boiler codes.

Safety first: never take the casing off a gas boiler. If you smell gas, open windows, don't use light switches, turn the gas off at the meter if you can and call your gas emergency number from outside. A carbon monoxide alarm going off means the same: switch the boiler off, get fresh air and call.

How to fix Worcester Bosch A7

Restart and test the hot water
Power the boiler off at the spur and back on, then run a hot tap. Take care: with a faulty sensor the water can come out hotter or cooler than usual.

When to call a technician

The sensor sits inside the boiler, so book a Gas Safe engineer to replace it.

Parts linked to A7

These are the parts an engineer usually checks for this code. They sit inside the sealed casing, so leave them to a Gas Safe registered engineer.

Frequently asked questions

Which Worcester Bosch models show the A7 code?

Greenstar CDi Classic ErP combis and HighFlow 440CDi and 550CDi ErP boilers, per their user instructions and the CDi engineer's booklet.

Can I fix Worcester Bosch A7 myself?

Only the outside checks above. If they don't clear A7, the fix is inside the boiler and needs a Gas Safe registered engineer.

Other Worcester Bosch boiler codes

Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.

Sources we checked