5206 on a Worcester Bosch Bosch Compress 5800i AW: Alarm: Z1 flow temperature sensor T0 fault
Short answer
On a Worcester Bosch heat pump, 5206 means: Alarm: Z1 flow temperature sensor T0 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: Alarm: Z1 flow temperature sensor T0 fault.
Part involved: flow temperature sensor T0.
When it shows: Alarm: Z1 flow temperature sensor T0 fault.
Likely causes:
- Lead between control unit and flow sensor; faulty sensor.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Clears when cause removed.
Manual reset: Reset/acknowledge via UI 800 fault menu after cause removed.
What you can check
- Read and note the full code (and sub-code) shown on the controller and pass it to your installer.
What the engineer will check
- Restore connection; test sensor against table; replace.
Who to ask for: heat pump installer / electrician.
Certification: Electrical work to BS 7671 by competent person.
What you might notice
Sources
- Installationsanleitung Bedienfeld UI 800 (Luft-Wasser-Wärmepumpe) 6721833375 ↗ · 6721833375 (2023/09) DE, AT, CH, LU · page 21 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026