# Diagnostics reference

> Look up heat-pump readings, controller restart reasons, device events and log behavior.

Source: https://serin-labs.com/controller/diagnostics.html
Last updated: 2026-10-27

## Heat-pump diagnostics

Available readings depend on the indoor unit.

Scroll sideways to read all columns.

| Firmware | Where to find diagnostics | Reported data |
| --- | --- | --- |
| HomeKit-compatible | Controller web interface | Compressor frequency, outside temperature, runtime hours, error codes, sub mode, and stage information. |
| ESPHome | Home Assistant, after adding Diagnostics through the generator | Nine sensors: compressor frequency, outside temperature, input power, energy use, runtime hours, heat-pump connection uptime, stage, sub mode, and auto sub mode. |
| Matter-compatible | Controller web interface | Compressor frequency, outdoor temperature, runtime, and error codes; these do not appear in Google Home, Alexa, or SmartThings. |

Outside temperature comes from the outdoor unit. Stage and sub modes describe its operating state. ESPHome diagnostic entities are enabled for history graphs when added through the generator.

On HomeKit-compatible and Matter-compatible firmware, **Heat Pump · CN105** shows "Error code E" followed by the indoor unit's code. Include it with [Copy Diagnostics](https://serin-labs.com/controller/support-info.html#diagnostics) in a support request.

For error codes or missing data, follow [CN105 troubleshooting](https://serin-labs.com/troubleshooting.html#cn105).

## Restart reasons and counters

On HomeKit-compatible and Matter-compatible firmware, **About** shows Wi-Fi Drops and Pump Link Drops since the last restart. Boots and Crashes count since the last factory reset.

**Last Reset** shows why the controller last started:

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| Value | What it means |
| --- | --- |
| `POWER_ON` | Power was switched on or restored. |
| `SW_RESTART` | The controller restarted itself: after an update, a pairing or Wi-Fi reset, or · **Restart Device** · . |
| `BROWNOUT` | The supply voltage dropped too low. Check the power source and the cable connections. |
| `PANIC` · , · `TASK_WDT` · , · `INT_WDT` · , · `WDT` | The firmware crashed and restarted. Include the diagnostics text in a support request. |

## Device events

On HomeKit-compatible and Matter-compatible firmware, **About** > **Device Events** retains 24 events through restarts, newest first. Select **Refresh** to load new ones. Before the clock is set, timestamps show `boot #N` and time since startup.

Scroll sideways to read all columns.

| Event | What happened |
| --- | --- |
| `BOOT` | The controller started. The reason follows in parentheses, using the · **Last Reset** · values above. |
| `CRASH` | The controller restarted after a crash. |
| `SAFE_MODE` | Repeated crashes started · [safe mode](https://serin-labs.com/controller/recovery.html#safe-mode) · . |
| `OTA` | A firmware update was installed. |
| `CN105_LOST` | The indoor unit stopped answering over the CN105 cable. |
| `CN105_OK` | The indoor unit answered again. |
| `CN105_ERROR` | The indoor unit reported an error code. |
| `RECOVERY_AP` | The backup setup network opened. |
| `HK_RESET` | App pairing was reset. |
| `WIFI_CREDS` | The saved Wi-Fi network changed. · `(erased)` · means it was erased. |

Repeated `CN105_LOST` events point to the cable or connector; see [CN105 troubleshooting](https://serin-labs.com/troubleshooting.html#cn105).

## Live log behavior

**Diagnostics · Logs** keeps the last 200 lines while the page is open. Closing it stops capture. **Debug** returns to **Info** after a restart.

## Capture evidence while the problem happens

Follow [Collect diagnostics for support](https://serin-labs.com/controller/support-info.html). Include error codes as displayed; this manual does not translate Mitsubishi service codes.