F33 on a Toshiba R32 Estia 1-Series: Flowing quantity failure
Short answer
On a Toshiba heat pump, F33 means: Flowing quantity failure. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Flowing quantity failure.
Part involved: circulation pump, flow switch/sensor, strainer, water pipework.
When it shows: TC >= 68C in heat pump heating/DHW (not defrost), or flow detected when built-in pump starts.
Likely causes:
- No or little water flow.
- Flow sensor defect.
- Flow sensor and low pressure sensor connectors swapped.
- Flow from external pump.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: no.
Manual reset: Cause must be fixed by an engineer; hardware faults reappear until repaired.
What you can check
- Note the check code shown on the remote controller and the outdoor/hydro model numbers before contacting an engineer.
- Check the system pressure gauge on the hydro unit / heating system shows the normal fill pressure the installer set (the manuals ask for at least about 1 bar); if it is low, report it to the engineer. Check the filling loop is closed.
- Check radiator/underfloor zone valves and thermostats are calling for heat and have not all been turned off.
What the engineer will check
- Follow manufacturer's check-code flowchart.
- No or little water flow.
- Flow sensor defect.
- Flow sensor and low pressure sensor connectors swapped.
- Flow from external pump.
Who to ask for: Heat pump / heating engineer (hydronic).
Certification: Heat pump installer competence (e.g. MCS-installer staff); no F-gas needed unless refrigerant work follows.
What you might notice
Sources
- Air to Water Heat Pump Service Manual - Wall Mounted Type (File No. AE0-2101W) ↗ · AE0-2101W · page p.114 (printed page; PDF page +1) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026