L2 on a Grant heat pump: Outdoor temperature sensor error

What it means

The manual says: Outdoor temperature sensor error.

Part involved: additional outdoor temperature sensor (terminal PCB).

When it shows: Detected by heat pump/controller PCB; error reset type printed as 'Auto'.

Likely causes:

• Outdoor temperature sensor (terminal PCB) faulty.

Is it safe?

The heat pump keeps running with some functions stopped.

Resetting itself: Auto: resets automatically once conditions return to normal (if the heat pump has stopped it may need a manual reset).

Manual reset: Engineer: press - and + on the remote controller together for 3 s, or press Reset SW on the Terminal PCB.

What you can check

• Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
• Grant advises homeowners NOT to reset Aerona3 fault codes themselves - leave the reset to the engineer.

What the engineer will check

• Check the resistance by tester; replace if faulty.

Who to ask for: Grant-trained (G1) heat pump engineer.

What you might notice

• Insufficient heating (house not warm enough)

What owners and engineers report

17 owner and engineer reports mention this.

• Insufficient heating (house not warm enough) on the Aerona³ R32: 17 reports

Sources

• Grant Aerona³ Air to Water High Efficiency Heat Pump Range - Installation and Servicing Instructions (UK DOC 0136) ↗ · Rev 2.4 · page 57 (DOC 0154: 56) · Reviewed 23 September 2026
• Grant UK Aerona³ Air to Water High Efficiency Heat Pump Range - Installation and Servicing Instructions (UK DOC 0109) ↗ · Rev 1.1 · page 56 (IRL DOC 0001: s11.4-11.5, printed pp55-57) · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026