IDM Heatpump Documentation
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Known Limitations

Device Compatibility

  • Navigator 10 has direct maintainer hardware confirmation. Navigator 2.0 and Navigator Pro are expected from the typed register model but still need complete diagnostics across current firmware variants.
  • Older IDM controllers without Navigator firmware are not supported
  • Modbus register mapping may vary slightly between firmware versions

Modbus TCP

  • Only Modbus TCP is supported (no serial Modbus RTU)
  • Port and Slave ID must be configured correctly
  • Some controller/firmware combinations tolerate only limited parallel Modbus clients. If timeouts correlate with another automation system, test with that client stopped or increase the polling interval

Write Frequency

  • Some Modbus registers are backed by EEPROM storage on the controller and tolerate only limited write cycles over the hardware lifetime.
  • The integration logs a warning when the same register address is written more than once within 5 seconds, which helps catch runaway automation loops.
  • For the raw write_register service, users must acknowledge the risk explicitly. No automatic hard-block prevents frequent EEPROM writes — treat unknown addresses with care.

Single Device per Configuration Entry

  • Multiple IDM heat pumps are supported. Each connection must have a unique host, port, and slave-ID combination.
  • For multiple heat pumps on the same bus: use separate Slave IDs and create a separate entry for each

Read-only Access to Certain Registers

  • Some registers are read-only (e.g., energy meters, temperature sensors)
  • Attempting to write to read-only registers may return a Modbus error
  • The write_register service deliberately permits an explicitly acknowledged custom address, but still validates datatype and numeric encoding. It cannot infer safe ranges, EEPROM behavior or semantics for unknown addresses — for experienced users only

Zone Modules

  • A maximum of 10 zone modules with up to 8 configurable rooms each is supported. Six rooms is the current Navigator 10 default; only configure physically present rooms.

Model and Firmware Evidence

  • Navigator 10 has direct maintainer hardware coverage.
  • Navigator 2.0 and Navigator Pro remain dependent on complete community diagnostics across firmware variants.
  • A responding probe address alone may not prove an optional feature exists; unavailable sentinels are considered where hardware evidence exists.
  • See Stability & Release Readiness for the current blockers before removing the beta label.
  • Zone module configuration is adjustable via options after initial setup
  • Rooms without a physical sensor may return -1.0 as a value (marked as unavailable)

Scheduled Updates Rather Than HA Push Updates

  • Home Assistant state is updated through scheduled Modbus and optional web refreshes. The integration does not currently expose unsolicited controller events as immediate Home Assistant push updates.
  • Changes made elsewhere become visible after the relevant refresh interval.

Firmware Version

  • The current firmware version is read as a diagnostic sensor (firmware_version)
  • Firmware updates directly from Home Assistant are not possible
  • Updates are done via the myIDM cloud portal or via a USB stick using the controller display's service menu, which your heating installer or iDM service operates at the controller's installer level.
  • The three local interfaces exposed by the controller (Modbus TCP 502, Navigator HTTP 80, Navigator 10 WebSocket 61220) do not carry any firmware-update endpoint. All candidate WebSocket controllers (firmware, update, upgrade, software, usb, upload, maintenance, system.update, system.firmware, system.software, system.usb) respond with provided controller [...] is not supported!. See Navigator Protocol Analysis for the full verified controller catalog.

Heat-sink Sensors Without Plate Heat Exchanger

The heat-sink block (return/flow temperature, flow rate, charging-pump signal) only exists on plants with a plate heat exchanger (Trennwärmetauscher). Without one, the controller reports the not-present sentinel (-1.0) for the whole block and the entities correctly show unavailable.

The flow-rate register (heat_sink_flow_rate, address 1072) is listed as UCHAR in the older revisions of the official IDM doc (Navigator 2.0 up to rev 12, Navigator 10 rev 0); newer revisions corrected it to FLOAT, matching the word-swapped FLOAT32 that field readings (discussion #516) proved the controller serves. Before integration 0.23.0-b8 (idm-heatpump-api 2.14.4) the UCHAR decode read one byte of the float's low word, which produced a spurious 0.0 L/min on plants without a plate heat exchanger and jumping, far-too-high values on plants with a live flow signal. The register is now read as a float: real flow values display correctly, not-present plants report unavailable, and when the web supplement serves a flowmeter value it fills in for the not-present register automatically. On plants without a plate heat exchanger and without a web flowmeter row, simply disable the entity — nothing is wrong with the heat pump.

Deliberately Not Implemented

  • Web-only does not replace all Modbus capabilities: Navigator 10/Pro supports selected writes, climate/water-heater cards and KNX data from web snapshots. Power registers for calculated COP, GLT forwarding and one-shot DHW boost still require Modbus. Navigator 2.0 HTTP is primarily a read-only supplement, with a separately supported clock action. See Protocol capabilities.
  • Global force_update: Not enabled by default. External time-series systems should use recorder/InfluxDB configuration or selected helper sensors to avoid unnecessary Home Assistant database load.
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