Heat pumps · Error codes · Warmflow
B04Warmflow · Zeno G-Series ground source heat pump GS08/GS16/GS03
B04 on a Warmflow Zeno G-Series ground source heat pump GS08/GS16/GS03: Probe B04 fault or disconnected - Heating return
Short answer
On a Warmflow heat pump, B04 means: Probe B04 fault or disconnected - Heating return. 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: Probe B04 fault or disconnected - Heating return.
Part involved: temperature sensor/thermistor.
Likely causes:
- The heating return temperature sensor is faulty or disconnected.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
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 return 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 Ground Source Heat Pumps G-Series GS08 / GS16 - User, Installation & Service Instructions (v6) ↗ · v6 · page 57 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026