Heat pumps · Error codes · Warmflow
P02aWarmflow · Zeno R290 air source heat pump AS01-R290/AS02-R290/AS03-R290
P02a on a Warmflow Zeno R290 air source heat pump AS01-R290/AS02-R290/AS03-R290: Mix Tube Outlet Water Temp. Sensor Fault
Short answer
On a Warmflow heat pump, P02a means: Mix Tube Outlet Water Temp. Sensor Fault. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Mix Tube Outlet Water Temp. Sensor Fault.
Part involved: temperature sensor/thermistor.
Likely causes:
- The temperature sensor is faulty or disconnected.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Note the exact code shown on the controller (a photo helps) and report it to your installer or the manufacturer's service line.
- Check the heat pump's supply breaker/isolator at the consumer unit is on (do not open any casing).
What the engineer will check
- Test the operation of the heating flow temperature sensor and re-connect/replace if necessary.
Who to ask for: heat pump controls / electrical.
Certification: Competent heat pump engineer; electrical competence for work inside the unit.
What you might notice
Sources
- Warmflow High Efficiency Variable Speed Air Source Heat Pumps A-Series AS01-R290 / AS02-R290 / AS03-R290 - User, Installation & Service Instructions, Guarantee (9009049 Rev D) ↗ · 9009049 Rev D · page 57 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026