Heat pumps · Error codes · Grant
BOIL IN OPnGrant · Aerona (1st generation)
BOIL IN OPn on a Grant Aerona: HP return sensor open
Short answer
On a Grant heat pump, BOIL IN OPn means: HP return sensor open. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: HP return sensor open.
Part involved: HP return sensor (BTC).
When it shows: Shown on the BTC controller display as 'Item Field' + 'Num Field'.
Likely causes:
- Return sensor open circuit / disconnected wire.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: Not stated.
Manual reset: Not stated.
What you can check
- Note the exact code shown on the controller display and tell your installer or Grant-trained engineer.
- Check the heat pump isolator switch and the consumer-unit breaker/RCD for the heat pump are ON (do not repeatedly reset a tripping breaker).
What the engineer will check
- Check sensor wires for security (common cause: loose/disconnected sensor wire, s13.5).
- Check sensor resistance against Figures 13-4/13-5.
- Replace sensor if faulty.
Who to ask for: Heat pump / heating controls engineer.
What you might notice
Sources
- Grant Aerona Air Source Heat Pump - Air to Water Heat Pump Range - Installation & User Instructions (DOC.87) ↗ · Rev.05 · page 37 (PDF p41) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026