F.9997 on a Glow-worm GeniaAir: Communication between the indoor unit and outdoor unit is not possible due to the different versions of the bus protocol
Short answer
On a Glow-worm heat pump, F.9997 means: Communication between the indoor unit and outdoor unit is not possible due to the different versions of the bus protocol. 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: Communication between the indoor unit and outdoor unit is not possible due to the different versions of the bus protocol.
Part involved: Communication between the indoor unit and outdoor unit is not possible due to th.
Likely causes:
- Replacement/spare part case for the control PCB or outdoor unit.
- Glow-worm trade page: Communication between indoor and outdoor unit not possible due to incorrect communication protocol Incorrect appliance interface, fault in the wiring or connection between the heat pump and heat pump interface, incorrect connection of Ebus components to communication connection between indoor and outdoor units.
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: no - the fault remains displayed until the cause is eliminated.
Manual reset: yes - after the cause is eliminated, press the reset button (indoor unit) or reset via the system control; if it recurs after several resets contact customer service.
What you can check
- Note the full code and text shown on the display (and the date/time it appeared). Check the heat pump supply breaker/isolator (and back-up heater breaker, if separate) at the consumer unit is on; if a breaker has tripped more than once, leave it off and call an engineer - do not open any casing. Glow-worm's MiPro Sense operating instructions say always contact your competent person in the event of a fault message; until they arrive you may select a limp-home (back-up heater) setting on the control, which is expensive to run.
What the engineer will check
- Ensure that the unit pairing is correct.
Who to ask for: Heat pump/controls installer familiar with Vaillant eBUS controls.
Certification: MCS installer certification; Vaillant product training recommended.
What you might notice
Sources
- GeniaAir Appliance Interface installation and maintenance instructions ↗ · 8000043014_01 · page HPIM 7 8000043014_01 p.34 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026