U8 on a Daikin Altherma HT: Malfunction of transmission between main and sub remote controls (malfunction of sub remote control)
Short answer
On a Daikin heat pump, U8 means: Malfunction of transmission between main and sub remote controls (malfunction of sub remote control). 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: Malfunction of transmission between main and sub remote controls (malfunction of sub remote control).
Part involved: user interface / room thermostat.
When it shows: Normal transmission does not continue for specified period.
Likely causes:
- Malfunction of transmission between main and sub remote control; Connection between sub remote controls; Defect of remote control PC board.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
What you can check
- Read the full error code shown on the user interface and note it, with the date/time, for your installer.
- Check any room thermostat/controller display is lit and its batteries (if battery-powered) are not flat; check thermostat and schedule settings.
What the engineer will check
- Follow the service-manual troubleshooting flow chart for this code: check malfunction of transmission between main and sub remote control; check connection between sub remote controls; check defect of remote control PC board.
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
What you might notice
Sources
- Service Manual Daikin ALTHERMA HT ERSQ/ERRQ 011-016 AA V1/Y1 + EKHBRD (ESIE09-08C) ↗ · ESIE09-08C · page 219 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026