VRC 720 (ID=72000, SW=0122, HW=7703): 12 messages fail with 'invalid position in decode'

[rmeekers]

Setup

• ebusd 26.1.26.1, CP2104 USB serial adapter
• Controller: scanned MF=Vaillant;ID=72000;SW=0122;HW=7703, loaded vaillant/15.720.csv
• Boiler: scanned MF=Vaillant;ID=BAI00;SW=0405;HW=9602, loaded vaillant/08.bai.csv

Problem

12 of 657 messages fail to decode. The controller answers with a single byte where the
definition expects a field at a further position:

720 SFMode     =  (ERR: invalid position for 3115b52406020000007400 / 00)
720 Z1DayTemp  =  (ERR: invalid position for 3115b52406020003000700 / 00)
720 HolidayTemp = (ERR: invalid position for 3115b52406020000000600 / 00)
bai Status     =  (ERR: invalid position for 3108b5110103 / 00)

Full list of affected messages:

circuit	messages
720	HolidayTemp, OpMode, OpModeCooling, OpModeEffect, OpModeVentilation, PrEnergySum, SFMode, Z1DayTemp, Z2DayTemp, Z3DayTemp
bai	Status, Status16

What works

The other 645 messages decode fine, including messages with very similar names on the same
circuits: HwcSFMode (auto), PrEnergySumHc (228), PrEnergySumHwc, Z1OpMode,
Z1SFMode, StorageTemp (42.19), StorageTempDesired, StorageTempMax. So this is
specific to these 12 definitions, not to the circuit or the adapter.

Side effect in Home Assistant

Four of these (HcStorageTempBottom, HcStorageTempTop, HwcStorageTempBottom,
HwcStorageTempTop) publish an empty payload over the MQTT/HA integration. Because an
empty retained publish deletes the retained message, the discovery config stays but the state
topic holds nothing, and every publish raises 'value_json' is undefined in Home Assistant.
Worked around locally with filter-non-name.

Possibly related: #248 (SFMode on VRC 720), #241, #332.

Happy to run further ebusctl commands or provide raw dumps if that helps.

[PiotrSien]

Confirming the same issue on Vaillant ecoTEC Exclusive 25 CS (BAI00, SW=0407, HW=7603), ebusd 26.1.8, Shield C6 Ethernet:

bai Status — all sub-fields stuck at unknown:

Status hcmode — unknown (last updated yesterday, never recovering)
Status press — unknown
Status temp — unknown

bai Status16 — unknown, also incorrectly published with unit_of_measurement: °C and device_class: temperature (should be a status field, not a temperature).

bai Status01 and Status02 — working correctly, confirming the issue is specific to the Status and Status16 definitions, not general connectivity.

This is consistent with what you described: selective decode failure on exactly these messages, while the majority decode fine.