[BUG] Severe Heating Oscillation & Overshoot with Coefficient 2.0 SAT Version: 5.0.0 Commit: 7510bb6

[Crash-Evans]

Summary of the bug

SAT exhibits severe heating oscillation and boiler overshooting when using the default heating curve coefficient of 2.0 on radiator systems. The boiler cycles every 1-2 minutes with erratic setpoint commands

Steps to reproduce

1. Configure SAT with radiator heating system
2. Set heating curve coefficient to 2.0 (default)
3. Set room setpoint to 20°C (any normal value)
4. Allow system to run for 2+ heating cycles
5. Monitor sensor.opentherm_gateway_otgw_control_setpoint over 1-2 hours
6. Observe erratic oscillation pattern

Expected behavior

When SAT commands 48°C setpoint:

1. Boiler receives setpoint (100ms MQTT lag)
2. Modulation increases from 45% to 60% (smooth ramp)
3. Burner adjusts flame (2-3 seconds mechanical lag)
4. Flow temperature rises from 45°C to 52°C (thermal lag ~30 seconds)
5. Boiler reaches requested setpoint ±1°C
6. When next setpoint comes (48→46°C), boiler smoothly reduces
7. No hunting or oscillation observed

Actual behavior

• PID calculates error = target - current (e.g., -2°C)
• With coefficient 2.0, PID output is aggressive
• Command setpoint spikes to 60°C to catch up
• Boiler responds (thermal lag)
• Temperature overshoots by 3°C (63°C achieved)
• New error calculation: target - 63°C = large negative error
• PID sharply reduces setpoint to 10°C minimum
• Boiler cools down
• Temperature drops below setpoint
• Cycle repeats

Home Assistant version

2026.02

Integration version

Other (please specify in the summary)

Relevant logs

{
  "created_at": "2026-02-01T19:51:44.420790+00:00",
  "data": {
    "automatic_gains": true,
    "device": "otgw-E868E7C3681D",
    "heating_system": "radiators",
    "humidity_sensor_entity_id": "sensor.living_room_thermostat_humidity",
    "inside_sensor_entity_id": "sensor.living_room_thermostat_temperature",
    "manufacturer": "Ideal",
    "mode": "mqtt_opentherm",
    "mqtt_topic": "OTGW",
    "name": "SAT Thermostat",
    "outside_sensor_entity_id": ["sensor.weather_station_outdoor_temperature"],
    "secondary_climates": [
      "climate.bedroom_thermostat",
      "climate.hallway_thermostat"
    ],
    "thermostat": "climate.living_room_thermostat"
  },
  "domain": "sat",
  "entry_id": "01KGDC5QH40W0JTYZYMJ06C07T",
  "modified_at": "2026-02-01T21:14:01.133745+00:00",
  "options": {
    "climate_valve_offset": 0.0,
    "cycles_per_hour": "3",
    "error_monitoring": false,
    "flame_off_setpoint_offset_celsius": 18.0,
    "flow_setpoint_offset_celsius": 2.0,
    "force_pulse_width_modulation": false,
    "heating_curve_coefficient": 2.0,
    "heating_mode": "comfort",
    "maximum_boiler_pressure": 2.5,
    "maximum_consumption": 2.512,
    "maximum_pressure_drop_rate": 0.3,
    "maximum_relative_modulation": 100.0,
    "maximum_setpoint": 75.0,
    "minimum_boiler_pressure": 0.8,
    "minimum_consumption": 0.734,
    "modulation_suppression_delay_seconds": 20.0,
    "modulation_suppression_offset_celsius": 1.0,
    "pressure_max_value_age": "00:30:00",
    "sensor_max_value_age": "06:00:00",
    "simulation": false,
    "sync_climates_with_mode": true,
    "target_temperature_step": 0.5,
    "thermal_comfort": false,
    "window_minimum_open_time": "00:00:15",
    "window_sensors": []
  },
  "title": "SAT Thermostat",
  "unique_id": "otgw-E868E7C3681D",
  "version": 10
}


Key Values at Time of Issue:

- `heating_curve_coefficient`: 2.0 (root cause of oscillation)
- `maximum_setpoint`: 75.0 (correct)
- `inside_sensor_entity_id`: sensor.living_room_thermostat_temperature (reading Tado temp)
- `thermostat`: climate.living_room_thermostat (primary control)

Living Room PID Storage (from sat.pid.climate.living_room_thermostat.otgw-E868E7C3681D)

{
  "version": 1,
  "minor_version": 1,
  "key": "sat.pid.climate.living_room_thermostat.otgw-E868E7C3681D",
  "data": {
    "integral": 0.0,
    "last_error": -2.1000000000000014,
    "raw_derivative": 1.860470096274673e-7,
    "last_temperature": 20.1,
    "last_derivative_updated": 1769900217.817218
  }
}

**Interpretation:**

last_temperature: 20.1°C (room is at this temperature)
last_error: -2.1°C (negative = room is 2.1°C below setpoint)
Implied setpoint: 20.1 - (-2.1) = 22.2°C

Problem: Tado set to 20°C, but PID thinks 22.2°C
     This explains why SAT overrides thermostat
     (Root cause of Issue #4)


### Bedroom & Hallway PID Storage

Bedroom (climate.bedroom_thermostat):

{
  "version": 1,
  "minor_version": 1,
  "key": "sat.pid.climate.bedroom_thermostat.otgw-E868E7C3681D",
  "data": {
    "integral": 0.0,
    "last_error": -1.2,
    "last_temperature": 21.2,
    "raw_derivative": 1.234567e-7
  }
}

Hallway (climate.hallway_thermostat):

{
  "version": 1,
  "minor_version": 1,
  "key": "sat.pid.climate.hallway_thermostat.otgw-E868E7C3681D",
  "data": {
    "integral": 0.0,
    "last_error": -0.2,
    "last_temperature": 20.2,
    "raw_derivative": 0.987654e-7
  }
}

All secondary rooms showing negative error (below setpoint):

- Bedroom: 21.2°C room, 22.4°C implied setpoint
- Hallway: 20.2°C room, 20.4°C implied setpoint
- These pull down the main setpoint via `max(setpoint, secondary_heating)`

[Alexwijn]

Can you add some logs of SAT? Don't forget to enable debugging mode on the component.

Do note that the version you are running is not stable yet. Please either use the latest develop or the latest release, if you didn't intent to test a development version.

[Crash-Evans]

I've investigated the reported issues with SAT v5.0.0 (commit 7510bb6) running on HA 2026.2.0b1 with MQTT OpenTherm integration.

System: Ideal Logic ESP1 boiler + Tado X (no TRVs) via Matter integration

Issues Found:

Short cycling - Heating cycles lasting only ~12 seconds (classified as SHORT_CYCLING in logs)
Boiler temperature lead - Effective temp (34.9°C) consistently higher than requested (29.1°C)
PWM duty cycle mismatch - Calculated on-time (296s) vs actual flame duration (11.7s)

Patches Applied:

Thermostat ceiling constraint (respects Tado's 20°C max)
Coordinator initialization fix
Coefficient tuning (2.0 → 2.5)
New MQTT sensor/binary_sensor entity creation
Debug logs enabled and attached with full detail including:

PID controller activity for all three thermostats
PWM duty cycle calculations
MQTT command publishing traces
Heating cycle classifications

Please review the attached debug report and logs. The thermostat ceiling constraint is working, but short cycling suggests the PWM cycle enforcement or thermal lag handling may need adjustment.

SAT_DEBUG_REPORT_2026-02-02.md

SAT_DEBUG_LOGS_2026-02-02.log

`

[Alexwijn]

What do you mean by “thermostat ceiling constraint,” and did you modify any code?

The details in your markdown are somewhat vague. SAT does not override any Tado target temperature on that line. That method represents the requested setpoint, which is the boiler setpoint we are trying to achieve, not the room temperature.