UF on a Worcester Bosch Greenstar Plus Hybrid: Safety device to protect against compressor overcurrent: compressor blocked
Short answer
On a Worcester Bosch heat pump, UF means: Safety device to protect against compressor overcurrent: compressor blocked. 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: Safety device to protect against compressor overcurrent: compressor blocked.
Part involved: external unit PCB / refrigerant circuit.
When it shows: Safety device to protect against compressor overcurrent: compressor blocked.
Likely causes:
- Overcurrent within 30 s of compressor start: shut-off valves closed; low supply voltage; wiring/plug/phase fault; compressor faulty; power board faulty; DIP switches wrong.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: Codes read via outdoor unit LEDs or service tool 7-716-161-051; SW1-2 DIP switch cancels fault displays (engineer).
What you can check
- Read and note the full FW200/hybrid manager fault code shown on the controller and pass it to your installer.
- Check the heat pump isolator and consumer-unit breaker(s) are switched on; if a breaker has tripped more than once, leave it off and call an engineer.
- Check the outdoor unit is not blocked by leaves, snow, ice or other debris (do not open the casing).
What the engineer will check
- Overcurrent within 30 s of compressor start: shut-off valves closed; low supply voltage; wiring/plug/phase fault; compressor faulty; power board faulty; DIP switches wrong.
Who to ask for: F-gas refrigeration engineer / heat pump installer.
Certification: F-gas certification (Category I) required for refrigerant circuit work; qualified electrician for electrical work.
What you might notice
Sources
- Installation and Maintenance Instructions Greenstar Plus Hybrid ↗ · 6 720 803 687 (2012/11) · page 61; 67 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026