What does the Atag 40 fault code mean?

Your boiler is struggling to accurately read the temperature of the water returning to it, which prevents it from heating your home reliably.

How much does it cost to fix Atag error code 40?

Typical repair cost for the Atag 40 fault is £150-250 including labour.

Return sensor error (e.g. open, short circuit, out of range)

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

7 signs repair isn't worth it anymore.

Break-even maths on monthly cover.

Realistic UK prices for a swap.