Grant Aerona P21 fault code
Grant Aerona heat pumps
What it means
DC water pump abnormal
Circulating pump operation fault.
UK models this code applies to
From the Grant service literature we hold (Grant Aerona 290 installation manual DOC0204 Rev 1.8, Table 11-1) — not a scraped list.
Aerona HPR2904 (4 kW)Aerona HPR29065 (6.5 kW)Aerona HPR2909 (9 kW)Aerona HPR29012 (12 kW)Aerona HPR290155 (15.5 kW)
Now the harder half: proving what caused it
P21 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.
Chase this code in the app →