High
AL28 on Pro A28

Your boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the water isn't flowing through the system correctly.

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.

What the manual says

Manufacturer manual

Temperature differential inverted (return sensor temperature higher than thermistors flowsensor temperature)

From this model's manual
Verified against the Pro A28 installation & service manual, page 22.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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.

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