BDR91 Overriding TPI behaviour

There are some circumstances where you may want to override the TPI settings of a BDR91, such as when using one for UFH, or when you have a S-plan configuration with OpenTherm.

This can be done by adding a second binding to the BDR91, the second binding being controlled by Home Assistant. The result is that the relay will be activated whenever either Evohome or Home Assistant enable it - effectively an OR function.

To achieve this you need to know the ids, and their hex equivalent, of the BDR91 and the HGI80/SSM.

The hex equivalent can be found with excel. With the id of the device in A1 (eg 18:136212), this formula in A2 will give you the hex equivalent (4A1414)

=DEC2HEX(BITLSHIFT(LEFT(A1,2),18)+VALUE(RIGHT(A1,6)))

Alternatively, use this python:

device_id = '18:136212' # a.k.a. 4A1414
print(f"{(int(device_id[:2]) << 18) + int(device_id[-6:]):0>6X}")

In the details below, the follow example devices are used:

BDR91 CH Relay 13:197705 (370449)
HGI80/SSM 18:136212 (4A1414)
Generic HGI80/SSM 18:000730 (used for sending but will be replaced by the HGI80/SSM)

The Process

The binding process involves sending a command, waiting for a response, and then sending an acknowledgment. The two strings you need to send are of the form below, where xxxxxx represents the hex device identifier of the HGI80/SSM. Note : The HGI80 won't send out a message as another device. You have to use 18:000730 instead. The examples below will work both on the HGI80 and the SSM.

I --- 18:000730 --:------ 18:136212 1FC9 012 000008xxxxxx001FC9xxxxxx
I --- 18:000730 13:197705 --:------ 1FC9 006 00FFFFxxxxxx

1. Do not clear any BDR91 bindings
2. Prepare the two strings that are required in a text editor you can cut and paste from. For the example devices these would be

I --- 18:000730 --:------ 18:136212 1FC9 012 0000084A1414001FC94A1414
I --- 18:000730 13:197705 --:------ 1FC9 006 00FFFF4A1414

3. Shutdown HA.
4. Connect your HGI80/SSM to a terminal emulator such as putty or the Arduino IDE, and confirm that you are seeing data packets
5. Put BDR91 into binding mode (5 second press till red led flashes)
6. Send the first of the two strings (I --- 18:000730 --:------ 18:136212 1FC9 012 0000084A1414001FC94A1414)
7. Wait for the BDR91 to return a W response (W --- 13:197705 18:136212 --:------ 1FC9 006 003EF0370449)
8. Send second string (I --- 18:000730 13:197705 --:------ 1FC9 006 00FFFF4A1414)
9. BDR91 should now be bound to the HGI80/SSM as well as the Evohome controller - led should have stopped flashing.

This is a sample packet log showing the process.

+ 11:10:22.860 -> 000  I --- 18:136212 --:------ 18:136212 1FC9 012 0B00084A14140B1FC94A1414
  11:10:23.747 -> 053  I --- 01:185426 --:------ 01:185426 0008 002 F906
+ 11:10:23.840 -> 062  W --- 13:197705 18:136212 --:------ 1FC9 006 003EF0370449
  11:10:24.119 -> 062  W --- 13:197705 18:136212 --:------ 1FC9 006 003EF0370449
  11:10:29.163 -> 053  I --- 04:003202 --:------ 01:185426 2309 003 0405DC
  11:10:29.163 -> 052  I --- 04:003202 --:------ 01:185426 12B0 003 040000
  11:10:31.068 -> 052  I --- 04:003202 --:------ 01:185426 12B0 003 040000
+ 11:10:38.987 -> 000  I --- 18:136212 13:197705 --:------ 1FC9 006 0BFFFF4A1414
  11:10:39.316 -> 062  I --- 10:048456 --:------ 10:048456 1FD4 003 002ED9
  11:11:15.940 -> 061  I --- 04:026298 --:------ 01:185426 3150 002 0600
  11:11:18.313 -> 053 RQ --- 01:185426 10:048456 --:------ 3EF0 001 00
  11:11:18.360 -> 061 RP --- 10:048456 01:185426 --:------ 3EF0 009 000010000000020A64

At this stage it is possible to test by sending either of these two strings:

On:
I --- 18:000730 --:------ 18:136212 0008 002 00C8

Off:
I --- 18:000730 --:------ 18:136212 0008 002 0000

It is worth noting that for some strange reason the green led does not always follow the relay state initially - it seems to take a few cycles for it to behave.

Service call

From within HA, use ramses_cc.send_packet to control the BDR91. For example, to enable the CH valve:

- alias: Enable CH Valve
  description: ''
  trigger:
  - platform: numeric_state
    entity_id: sensor.f9_relay_demand
    above: 5
  condition: []
  action:
  - service: ramses_cc.send_packet
    data:
      device_id: "18:000730"
      verb: I
      code: '0008'
      payload: '00C8'
  mode: single

Note for the service calls you must use the HGI80/SSM internal id (18:000730) for the destination. It will not work if you use any other id.

Keep Alive

One issue you may find is that the BDR91 thinks it has lost connection with the HGI80/SSM if you only activate it occasionally, in which case you should implement an automation that fires periodically:

- alias: CH Watchdog
  description: ''
  trigger:
  - platform: time_pattern
    minutes: /10
  condition: []
  action:
  - if:
    - condition: numeric_state
      entity_id: sensor.f9_relay_demand
      above: 5
    then:
    - service: ramses_cc.send_packet
      data:
        device_id: "18:000730"
        verb: I
        code: '0008'
        payload: '00C8'
    else:
    - service: ramses_cc.send_packet
      data:
        device_id: "18:000730"
        verb: I
        code: '0008'
        payload: '0000'
  mode: single