HomeKit climate accessory repeatedly becoming “Unavailable” in Home Assistant (Bedroom 3 only)

I’m hoping someone has seen this before.

My heating is controlled entirely by Home Assistant using the HomeKit Device integration with a tado° V3+ system. I am not using the official Tado integration because of authentication issues, and there are no Tado schedules active.

Everything generally works well except one room.

Problem:
One climate entity (climate.bedroom_3_up) repeatedly becomes Unavailable for a few minutes before reconnecting. It then repeats this throughout the day.

The history looks like this:

  • Heat
  • Unavailable
  • Heat
  • Unavailable
  • Heat
  • Unavailable

(see attached screenshot)

The rest of the HomeKit accessories remain online.

My setup:

  • Home Assistant 2026.7.x
  • HomeKit Device integration
  • tado° V3+ Internet Bridge
  • Wired Ethernet network
  • mDNS enabled
  • Home Assistant Green
  • Bedroom 3 Smart Radiator Thermostat

I’ve already tried:

  • Restarting Home Assistant
  • Restarting the Tado bridge
  • Rebooting networking equipment
  • Removing and re-adding HomeKit
  • Checking Wi-Fi signal (appears OK)
  • Confirmed this is only affecting Bedroom 3

Questions:

  1. Has anyone seen a single HomeKit climate accessory repeatedly become unavailable while the rest remain connected?
  2. Is this usually a HomeKit/mDNS issue, or is it more likely the individual Tado radiator valve?
  3. Are there any Home Assistant logs or HomeKit debug logs that are particularly useful for diagnosing this?

Any ideas would be much appreciated.