TRM132M exposes pump-related information through Modbus registers, but no single value proves which pump is energized, whether pressure is present, and whether the active pump is healthy. Read the output-state masks and circuit-status data together.
Read MP1 Pump Outputs as a Word
Read address 320 with Modbus function code FC3. The returned Word is a bit mask representing the outputs of the MP1 expansion module. FC2 is not interchangeable: the evidence reports all-zero FC2 responses because this status is exposed as a register value rather than as Modbus discrete inputs.
A captured value of 0001 0101 was interpreted as the makeup pump active and both heating and domestic-hot-water circuits operating on pump 2. Do not reuse that interpretation until the installed register map or OPC template confirms which MP1 output corresponds to each bit; the evidence does not establish the complete bit-to-output order.
Correlate Output Commands with Pressure Inputs
Read address 288 as another Word bit mask. Only five bits were reported as used in the examined controller. A captured value of 0001 1000 indicated active signals on inputs C4 and C5, identified as the pump-fault sensor inputs associated with circuit pressure.
Treat these inputs as pressure or fault-feedback indications, not direct identification of the running pump. A commanded MP1 output plus the expected C4 or C5 feedback supports an operational assessment, but the available evidence does not define the input polarity, response delay, or a rule that independently proves pump health.
Determine Circuit and Backup-Pump State
| Data | Address | Type or access | Supported use |
|---|---|---|---|
| MP1 output states | 320 | Word via FC3 | Decode the expansion-module output bit mask |
| Input states | 288 | Word via FC3 | Check C4 and C5 pressure/fault feedback |
| Heating circuit mode | 128..135 | String | Read the current heating-circuit mode |
| DHW circuit mode | 166..173 | String | Read the current domestic-hot-water circuit mode |
| DHW backup-pump parameter | 346 | Enum | Meaning of a zero value is not confirmed by the evidence |
The controller's own output states are available under the OPC template path corresponding to operational parameters, output devices, and state. The evidence does not provide their direct Modbus addresses, so obtain those mappings from the applicable register map or OPC polling template instead of inferring them from address 320.
Verification Procedure
- Read address 320 with FC3 and preserve the complete Word before extracting bits.
- Map each asserted bit to an MP1 output using the register map or OPC template for the installed configuration.
- Read address 288 and correlate C4 and C5 feedback with the commanded heating and DHW pump outputs.
- Read heating mode from 128..135 and DHW mode from 166..173 to identify the circuit operating state.
- Read the controller's own output-state items through the documented mapping to determine whether a backup-pump output is active. Do not use address 346 alone until its Enum values are defined.
- Verify failure handling by comparing the commanded primary or backup output with the corresponding pressure feedback. The evidence does not identify a dedicated register that conclusively reports backup-pump failure.
FAQ
Which Modbus register shows TRM132M pump outputs?
Read address 320 with FC3. It returns a Word whose bits represent MP1 expansion-module output states; confirm the bit-to-output mapping before assigning pump names.
Why does FC2 return zeros for the TRM132M output state?
The observed output state is exposed at address 320 as a register Word, so read it with FC3. FC2 queries the discrete-input data model and returned zeros in the documented case.
How can Modbus detect that a backup pump has failed?
Correlate the documented backup-pump output state with C4 or C5 pressure/fault feedback from address 288. No dedicated backup-pump-failure register or confirmed interpretation of address 346 is established by the available evidence.