Sinclair Ontario Heat Pump

Modbus RTU

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Last updated: 03. 2026

The Sinclair S-Therm Ontario (SMH-xxxIRB series) is a DC inverter air-to-water monoblock heat pump that connects to TapHome via Modbus RTU over RS-485. The template provides comprehensive control of heating, cooling, hot water production, floor commissioning, disinfection, and weather-dependent operation. The heat pump uses R32 refrigerant and is available in 1-phase (4–16 kW) and 3-phase (10–16 kW) variants.

The template exposes 38 devices covering temperature sensors, setpoint controls, operation modes, timer functions, and outdoor unit diagnostics with monitoring of 50+ error and protection coils.

Hardware connection

Indoor unit PCB overview

Sinclair Ontario indoor unit PCB layout showing RS-485 connectors CN1-CN4

The indoor unit PCB has 4 RS-485 connectors for Modbus communication:

Connector	Type	Pinout
CN1	RS-485 with 12V (4-pin)	1: +12V, 2: B, 3: A, 4: GND
CN2	RS-485 without 12V (4-pin)	1: B, 2: A
CN3	RS-485 without 12V (3-pin)	B, A
CN4	RS-485 with 12V (4-pin)	1: GND, 2: B, 3: A, 4: +12V

For TapHome: Use connector CN3 (3-pin, RS-485 without 12V) or CN2 (4-pin, RS-485 without 12V) for the BMS connection to TapHome Core:

B → B-/D- on TapHome RS-485
A → A+/D+ on TapHome RS-485

Wired controller RS-485 interface

The wired controller provides two communication interfaces:

Interface	Type	Pinout	Use
1 — BMS	2-wire, AWG24 twisted pair	1: B, 2: A	Connect to BMS/TapHome via RS-232 to RS-485 converter
2 — +12VDC	4-wire, AWG24, 8m max	1: +12VDC, 2: B, 3: A, 4: GND	Equipment communication line (powered by equipment)

Important — Interface 1 outputs RS-485 signals. If connecting through the wired controller BMS port, an RS-232 to RS-485 converter is required. For direct RS-485 connection, use the indoor unit PCB connectors (CN1–CN4) instead.

Technical specifications

Communication: Modbus RTU, RS-485
Baud rate: 9600, no parity, 1 stop bit
Slave ID range: 1–253 (default 1)
Cable: AWG24 twisted pair, Class V
Protocol: Read Multiple Coils (0x01), Read Multiple Registers (0x03), Write Multiple Coils (0x0F), Write Multiple Registers (0x10)

Configuration

Setting the Modbus address

The Modbus Slave ID is configured via the wired controller touchscreen:

Power on the controller, press COMMISSION to access the COMMISSION page
Press FUNCTION to go to the FUNCTION page
Press Next (rightmost button) to navigate to FUNCTION page 4/4 where “Address” is displayed
Select Address and use + / - to set the desired value (range 1–253, default 1)
Press OK to save

Sinclair Ontario wired controller COMMISSION menu for Modbus address setup

Sinclair Ontario address setting screen showing range 1-253

Address 0 and 126 cannot be used. Address 0 is reserved for broadcast (received by all units), and address 126 is reserved.

Communication precautions

Operation modes can only be changed when the unit is OFF
For heating-only units, “Cool” and “Cool+Hot water” settings are ineffective
When the water tank is unavailable, “Hot water”, “Cool+Hot water”, and “Heat+Hot water” modes are ineffective
Parameter modifications with memory function activated work immediately but are memorized after 30 minutes

Device capabilities

Power and operation mode

ON/OFF (H:42) — turns the heat pump on or off. Uses special encoding: 0xAA (170) = ON, 0x55 (85) = OFF. The ON/OFF state is shared across multiple devices (Holiday Mode, Manual Defrost, and Floor Debug check it before allowing changes)
Operation Mode (H:2) — selects Heat, Hot water, Cool+Hot water, Heat+Hot water, or Cool. Modes can only be changed when the unit is OFF. The template warns if a water-related mode is selected but no water tank is available

Temperature setpoints

The template provides separate setpoints for each control scenario:

Water Outlet Temperature Heating Setpoint (H:10) — target water outlet temperature for heating, 20–60°C (high-temp) or 20–55°C (low-temp), default 45°C
Water Outlet Temperature Cooling Setpoint (H:9) — target water outlet temperature for cooling, 7–25°C, default 18°C
Room Temperature Heating Setpoint (H:12) — room temperature target for heating, 18–30°C, default 20°C (active only when Control State is set to T-room)
Room Temperature Cooling Setpoint (H:11) — room temperature target for cooling, 18–30°C, default 24°C (active only when Control State is set to T-room)
Control State (C:17) — switches between water outlet temperature control (T-water out) and room temperature control (T-room). Has a service attribute showing whether a remote room sensor is installed (C:33), and a service action to configure it

Temperature monitoring

The template reads 9 temperature sensors from the heat pump, all using ÷10 conversion from raw register values:

Outdoor Temperature (H:118) — ambient outdoor air temperature
Water Outlet Temperature (H:125) — water leaving the plate heat exchanger
Water Inlet Temperature (H:127) — water entering the plate heat exchanger
Gas Pipe Temperature (H:130) — refrigerant vapor line temperature
Liquid Pipe Temperature (H:131) — refrigerant liquid pipe temperature
Discharge Pressure (H:124) — compressor discharge pressure as saturated temperature equivalent
Optional Water Sensor (H:126) — optional water temperature sensor reading
Remote Room Temperature (H:129) — remote room sensor reading (warns if remote sensor is not available)
Hot Water Tank (H:128) — current water tank temperature with setpoint control (H:13, range 40–80°C)

Hot water tank

Hot Water Tank reads the current tank temperature (H:128, ÷10) and controls the desired temperature (H:13, range 40–80°C, default 50°C). The ReadScript monitors whether a water tank is installed (C:29) and checks for sensor errors (C:156).

Six service attributes provide additional monitoring:

Water Tank Heater State, Tank Heater Logic, Other Thermal Logic
Delta-T hot water (2–8°C), Cool+Hot Water Priority, Heat+Hot Water Priority

Four service actions allow configuration of tank heater logic, hot water differential, and mode priorities.

Temperature differentials

Three thermostat devices control hysteresis bands:

Delta-T Cooling (H:29) — cooling temperature differential, 2–10°C, default 5°C
Delta-T Heating (H:30) — heating temperature differential, 2–10°C, default 10°C
Delta-T Room Temperature (H:32) — room temperature differential, 1–5°C, default 2°C

Weather-dependent operation

Weather-Dependent Operation (C:22) enables automatic adjustment of setpoints based on outdoor temperature. When enabled, heating and cooling setpoints are recalculated according to weather curves.

Six service attributes display the current curve parameters:

AT-Heat / AT-Cool — ambient temperature lower/upper bounds
RT-Heat / RT-Cool — room temperature lower/upper bounds
WT-Heat / WT-Cool — water temperature lower/upper bounds

Timers and scheduling

Weekly Timer (C:8) — enables/disables weekly timer schedule
Clock Timer (C:9) — enables/disables clock timer function
Temperature Timer (C:10) — enables/disables temperature-based timer function

Comfort and energy features

Quiet Mode (C:21) — reduces running noise via automatic compressor and fan speed control. Available in cooling, heating, and water heating modes
Fast Hot Water (C:18) — runs heat pump + water tank e-heater simultaneously for faster hot water production
Solar Heater (C:16) — enables solar heater priority for energy conservation. Warns if solar is not available. Has a service attribute and action for configuring solar availability (C:31)
Holiday Mode (C:34) — keeps indoor/water temperature in range to prevent freezing. Only for heating. Requires system OFF to enable
Emergency Mode (C:26) — enables emergency heating via e-heater only when outdoor unit fails

E-heater and auxiliary configuration

Optional E-Heater (H:3) — configures auxiliary electric heater count: 1 set, 2 sets, or Off
E-Heater Activation Temperature (H:14) — outdoor temperature threshold for e-heater activation, -20 to 18°C, default -15°C

Thermostat

Thermostat Configuration (H:39) — configures external thermostat connection type: Without, Air, or Air+Hot water
Thermostat State (H:132) — reads external thermostat demand: Cool, Heat, or Off

Floor commissioning

Floor Commissioning (C:25) manages the floor preheating process for initial floor heating system use. The system must be turned OFF before enabling.

Four service attributes monitor the commissioning process:

Floor Debug Segments (1–10 sections), Period 1 Temperature (25–35°C)
Delta-T of Segment (2–10°C), Segment Time (12–72 hours)

Six service actions control the process: Enable, Start, Stop, and individual parameter configuration.

Disinfection

Disinfection (H:135 read / C:23 write) manages the water system disinfection cycle with status reporting: Off, Running, Done, or Failed. A service attribute shows the disinfection temperature setpoint (H:4, range 40–70°C, default 70°C), and three service actions allow setting the temperature, starting, and stopping the cycle.

Maintenance functions

Manual Defrost (C:36) — triggers a manual defrost cycle. Requires system OFF to enable
Force Mode (H:40) — for refrigerant recovery and debugging only: Force-cool, Force-heat, or Off
Air Removal (H:41) — purges air from the water system: Air, Water tank, or Off

Outdoor unit diagnostics

Outdoor Unit Status (H:117) reports the current unit state: Cool, Heat, Hot water, or Off. The ReadScript monitors 38 error and protection coils across three groups:

Outdoor unit errors (C:88–C:109): Ambient/defrost/discharge/suction sensor errors, fan error, high/low pressure protection, capacity DIP setting error, economizer sensor errors, system recoverable/irrecoverable protection, flow switch protection, 4-way valve error

Drive/compressor errors (C:128–C:151): DC bus voltage errors, AC current protection, IPM/PFC errors, startup error, phase loss, compressor overcurrent, over-speed, desynchronizing, stalling, drive communication error, radiator/IPM overtemperature, charging circuit error, AC input voltage error

Indoor unit sensor errors: Condenser/e-heater/refrigerant liquid/vapor/water tank sensor errors, remote room sensor error

Twelve service attributes provide component-level monitoring:

Compressor State, Fan State, 4-way Valve State
Crankcase Heater, Underpan Heater, Defrosting State, Oil Return State
T-discharge, T-defrost, T-suction, T-economizer in/out (all ÷10 °C)

Module-level service attributes and actions

The module exposes 11 service attributes for system configuration monitoring:

T-HP max — maximum heat pump outlet temperature (40–55°C)
Cool/Heat run time — minimum compressor run time per mode
Water Pump State — indoor unit water pump On/Off
Other thermal — whether other thermal source is enabled, with logic mode and switch-on temperature
Other Heat Source State — On/Off status
Optional E-Heater logic — e-heater logic mode
Current limit value — maximum current limit (0–50 A)
Power limit — power limit in kW (register value x 10)

Ten service actions allow configuration of these parameters, plus an Error Reset action (H:44) to clear faults.

Additional capabilities

The heat pump also exposes registers for gate-card control (C:11), refrigerant recovery (C:35), manual 2-way valve control (C:37), floor debug temperature and remaining time readback (H:133–H:136), weather-dependent calculated setpoint (H:137), and compressor setting/running frequency (H:142–H:143). Communication error coils between the wired controller and indoor/outdoor units and drive (C:64–C:66) are also available. These can be added in a future template update.

Troubleshooting

No Modbus communication

Check RS-485 cables:
- B wire correctly connected to B-/D- on TapHome
- A wire correctly connected to A+/D+ on TapHome
- If using wired controller Interface 1, ensure an RS-232 to RS-485 converter is installed
Verify the Modbus Slave address on the wired controller (COMMISSION → FUNCTION 4/4 → Address)
Confirm TapHome is set to: 9600 baud, no parity, 1 stop bit
Try using the indoor unit PCB connectors (CN1–CN4) directly instead of the wired controller BMS port

Mode changes not working

Verify the unit is OFF before changing the operation mode — mode changes are blocked while the unit is running
Check that the water tank is installed (C:29) if selecting Hot water, Cool+Hot water, or Heat+Hot water modes
For heating-only units, Cool and Cool+Hot water modes are ineffective

Holiday Mode / Manual Defrost not activating

The unit must be OFF (H:42 = 0x55) before these functions can be enabled
The template WriteScript checks the ON/OFF state and shows a warning if the system is on

Sensor errors appearing in TapHome

Check the specific error coil in the Outdoor Unit Status service attributes
For indoor unit sensor errors (C:152–C:160), inspect the corresponding temperature sensor connections on the PCB
Use the Error Reset service action (H:44) to clear recoverable faults after resolving the issue

Available devices

Sinclair Ontario Module

Service Attributes

T-HP max [°C]	reads H:16 (UInt16); maximum heat pump outlet temperature, range 40–55°C, default 50°C
Cool run time [min]	reads H:33 (UInt16); minimum compressor run time in cooling mode, range 1–10 min, default 3 min
Heat run time [min]	reads H:34 (UInt16); minimum compressor run time in heating mode, range 1–10 min, default 5 min
Water Pump State	reads C:175 (Bool); On/Off status of indoor unit water pump
Other thermal	reads C:27 (Bool); With/Without — whether other thermal source is enabled
Other thermal logic	reads H:35 (UInt16); other thermal source logic mode 1–3
T-Other switch on [°C]	reads H:15 (Int16); outdoor temperature threshold for other thermal source activation, range -20 to 18°C
Other Heat Source State	reads C:169 (Bool); On/Off status of other heat source
Optional E-Heater logic	reads H:37 (UInt16); optional e-heater logic mode 1–2
Current limit value [A]	reads H:38 (UInt16); maximum current limit, range 0–50 A, default 16 A
Power limit [kW]	reads H:43 (UInt16) × 10; power limit in kW (register value × 10), range 0–10 kW

Service Actions

Set T-HP max	writes H:16 (UInt16); range 40–55°C
Set Cool run time	writes H:33 (UInt16); range 1–10 min
Set Heat run time	writes H:34 (UInt16); range 1–10 min
Set Other thermal	writes C:27 (Bool); 0=Without, 1=With
Set Other thermal logic	writes H:35 (UInt16); range 1–3
Set T-Other switch on	writes H:15 (Int16); range -20 to 18°C
Change Optional E-Heater logic	writes H:37 (UInt16); range 1–2
Change Current limit value	writes H:38 (UInt16); range 1–50 A
Change Power limit	writes H:43 (UInt16); value in 0.1 kW units, range 1–100 (= 0.1–10 kW)
Reset error	writes H:44 (UInt16); 0=Does not clear fault, 1=Clear fault

Sinclair Ontario

Service Attributes

T-HP max [°C]

modbusr(H, 16, uint16)

Cool run time [min]

modbusr(H, 33, uint16)

Heat run time [min]

modbusr(H, 34, uint16)

Water Pump State

if(modbusr(c, 175, bool), "On", "Off")

Other thermal

if(modbusr(c,27,bool), "With", "Without")

Other thermal logic

modbusr(h,35,uint16)

T-Other switch on [°C]

MODBUSR(H, 15, Int16)

Other Heat Source State

if(modbusr(c, 169, bool), "On", "Off")

Optional E-Heater logic

modbusr(h,37,uint16)

Current limit value [A]

modbusr(h,38,uint16)

Power limit [kW]

modbusr(h,43,uint16) * 10

Service Actions

Set T-HP max

Parameters: T-HP max (40–55 C)

modbusw(H, 16, uint16, C)

Set Cool run time

Parameters: Cool run time (1–10 min)

modbusw(H, 33, uint16, min)

Set Heat run time

Parameters: Heat run time (1–10 min)

modbusw(H, 34, uint16, min)

Set Other thermal

Parameters: Other thermal

modbusw(c, 27, bool, ot)

Set Other thermal logic

Parameters: Logic (1–3 lo)

modbusw(h,35,uint16,lo)

Set T-Other switch on

Parameters: T-Other switch on (-20–18 temperature)

modbusw(h,15,int16,temperature)

Change Optional E-Heater logic

Parameters: Logic (1–2 lo)

modbusw(h,37,uint16,lo)

Change Current limit value

Parameters: limit (1–50 lo)

modbusw(h,38,uint16,lo)

Change Power limit

Parameters: Value [0.1 * kW] (1–100 val)

modbusw(h,43,uint16,val)

Reset error

Parameters: Parameter1

modbusw(h,44,uint16,Abr1)

Delta-T Cooling Thermostat

Cooling temperature differential — controls hysteresis band around cooling setpoint (2–10°C)

Delta-T Heating Thermostat

Heating temperature differential — controls hysteresis band around heating setpoint (2–10°C)

Delta-T Room Temperature Thermostat

Room temperature differential for thermostat on/off cycling (1–5°C)

Air Removal Multi-value Switch

Water system air purge — Air, Water tank, or Off

Values / States: Air · Water tank · Off

Clock Timer Switch

Control State Switch

Selects control mode — T-water out (water outlet temperature) or T-room (room temperature)

Values / States: T-room · T-water out

Service Actions

Set Remote sensor

Control State

Read switch state

MODBUSR(C, 17, Bool)

Write switch state

MODBUSW(C, 17, Bool, St)

Read (module)

if(modbusr(c, 160, bool), adderror("Remote Room Temp Sensor Error"));

Service Attributes

Remote sensor

if(modbusr(C, 33, bool), "With", "Without")

Service Actions

Set Remote sensor

Parameters: Remote sensor

modbusw(C, 33, bool, rs)

Discharge Pressure Temperature Sensor Read-only

Compressor discharge pressure as saturated temperature equivalent

Disinfection Multi-value Switch

Water system disinfection cycle status — Off, Running, Done, or Failed

Values / States: Off · Running · Done · Failed

Service Actions

Set Disinfection Temp

Start Disinfection

Stop Disinfection

Disinfection

Read switch state

MODBUSR(H, 135, uInt16)

Write switch state

if (Mu = 1, modbusw(C, 23, bool, 1));
if (Mu = 0 or Mu = 2, modbusw(C, 23, bool, 0));

Service Attributes

Disinfection Temp [°C]

modbusr(H, 4, uint16)

Service Actions

Set Disinfection Temp

Parameters: Disinfection Temp (40–70 C)

modbusw(H, 4, uint16, C)

Start Disinfection

modbusw(C, 23, bool, 1)

Stop Disinfection

modbusw(C, 23, bool, 0)

Emergency Mode Switch

Emergency heating via e-heater only — activates when outdoor unit fails

Fast Hot Water Switch

Simultaneous heat pump + e-heater operation for faster water heating

Floor Commissioning Reed Contact Read-only

Floor preheating process for initial floor heating system use — requires system OFF

Service Attributes

Floor Debug Segments

Floor Debug Period 1 temp

Delta-T of segment

Segment time

Service Actions

Enable Floor Debug

Start Floor Debug

Stop Floor Debug

Set Floor Debug Segments

Set Floor Debug Period 1 temp

Set Delta-T of segment

Set Segment time

Floor Commissioning

Read

MODBUSR(C, 25, Bool)

Service Attributes

Floor Debug Segments

modbusr(H,5,uint16)

Floor Debug Period 1 temp [°C]

modbusr(H,6,uint16)

△T of segment [°C]

modbusr(h,7,uint16)

Segment time [hours]

modbusr(h,8,uint16)

Service Actions

Enable Floor Debug

Parameters: On/Off

if sw = 0
    MODBUSW(C, 24, Bool, 0);
else
    if on_off = 0
        MODBUSW(C, 24, Bool, 1);
    else
        return("Please turn off the system first");
    end
end

Start Floor Debug

MODBUSW(C, 25, Bool, 1)

Stop Floor Debug

MODBUSW(C, 25, Bool, 0)

Set Floor Debug Segments

Parameters: Sections (1–10 se)

modbusw(H,5,uint16,se)

Set Floor Debug Period 1 temp

Parameters: Temperature (25–35 C)

modbusw(h,6,uint16,C)

Set △T of segment

Parameters: Temperature (2–10 C)

modbusw(h,7,uint16,C)

Set Segment time

Parameters: Time (12–72 h)

modbusw(h,8,int16,h)

Force Mode Multi-value Switch

Forced operation for refrigerant recovery and debugging only — not for normal use

Values / States: Force-cool · Force-heat · Off

Holiday Mode Switch

Keeps indoor/water temperature in range to prevent freezing — heating only, requires system OFF

Holiday Mode

Read switch state

MODBUSR(C, 34, Bool)

Write switch state

if on_off = 0
    MODBUSW(C, 34, Bool, St);
else
    counter := 10;
end

Read (module)

if counter > 0
    addwarning("Please turn off the system first!");
    counter := counter -1;
end

Hot Water Tank Thermostat

Water tank temperature and setpoint control (40–80°C) with heater state and priority monitoring

Service Attributes

Water Tank Heater State

Tank heater Logic

Other thermal logic

Delta-T hot water

Cool+Hot Water Priority

Heat+Hot Water Priority

Service Actions

Set Tank heater Logic

Set Delta-T hot water

Set Cool+Hot Water Priority

Set Heat+Hot Water Priority

Hot Water Tank

Read temperature

MODBUSR(H, 128, Int16)/10

Read desired temperature

MODBUSR(H, 13, uInt16)

Write desired temperature

MODBUSW(H, 13, uInt16, round(Se))

Read (module)

water_tank := modbusr(C, 29, bool);

if(!water_tank, adderror("No Water Tank Installed"));
if(modbusr(c, 156 , bool), adderror("Water Tank Temp Sensor Error"));

Service Attributes

Water Tank Heater State

if(modbusr(c, 173, bool), "On", "Off")

Tank heater Logic

modbusr(H, 36, uint16)

Other thermal logic

modbusr(H, 35, uint16)

△T-hot water [°C]

modbusr(H, 31, uint16)

Cool+Hot Water Priority

if(modbusr(c, 19, bool), "Hot water", "Cool")

Heat+Hot Water Priority

if(modbusr(c, 20, bool), "Hot water", "Heat")

Service Actions

Set Tank heater Logic

Parameters: Logic (1–2 L)

modbusw(H, 36, uint16, L)

Set △T-hot water

Parameters: △T (2–8 C)

modbusw(H, 31, uint16, C)

Set Cool+Hot Water Priority

Parameters: Priority

modbusw(C, 19, bool, P)

Set Heat+Hot Water Priority

Parameters: Priority

modbusw(C, 20, bool, P)

Manual Defrost Switch

Triggers manual defrost cycle — requires system OFF

Operation Mode Multi-value Switch

Heat pump operating mode — Heat, Hot water, Cool+Hot water, Heat+Hot water, or Cool

Values / States: Heat · Hot water · Cool+Heat water · Heat +Hot water · Cool

Operation Mode

Read switch state

var ret := MODBUSR(H, 2, uInt16);

if( !water_tank and (ret = 2 or ret = 3 or ret = 4), addwarning("Water tank is unavailable"));

return(ret)

Write switch state

MODBUSw(H, 2, uInt16,Mu)

ON/OFF Switch

ON/OFF

Read switch state

var status := MODBUSR(H, 42, uint16);

if status = 0xAA
    on_off := 1;
    return(1);
else
    on_off := 0;
    return(0);
end

Write switch state

if St = 0
    MODBUSW(H, 42, uint16, 0x55);
else
    MODBUSW(H, 42, uint16, 0xAA);
end

Optional E-Heater Multi-value Switch

Auxiliary electric heater configuration — 1 set, 2 sets, or Off

Values / States: 1 set · 2 sets · Off

Outdoor Unit Status Multi-value Switch Read-only

Outdoor unit operating state with 38 error/protection coil monitoring and component diagnostics

Values / States: Cool · Heat · Hot water · Off

Outdoor Unit Status

Read switch state

MODBUSR(H, 117, uInt16)

Read (module)

if(modbusr(c, 88 , bool), adderror("Ambient Temp Sensor Error"));
if(modbusr(c, 89 , bool), adderror("Defrost Temp Sensor Error"));
if(modbusr(c, 90 , bool), adderror("Discharge Temp Sensor Error"));
if(modbusr(c, 91 , bool), adderror("Suction Temp Sensor Error"));
if(modbusr(c, 92 , bool), adderror("ODU Fan Error"));
if(modbusr(c, 93 , bool), adderror("High-Pressure Sensor Error"));
if(modbusr(c, 94 , bool), adderror("High Pressure Protection"));
if(modbusr(c, 95 , bool), adderror("Low Pressure Protection"));
if(modbusr(c, 96 , bool), adderror("High Discharge Protection"));
if(modbusr(c, 97 , bool), adderror("Capacity DIP Setting Error"));
if(modbusr(c, 98 , bool), adderror("Communication Error between IDU and ODU"));
if(modbusr(c, 99 , bool), adderror("Economizer In Sensor Error"));
if(modbusr(c, 100 , bool), adderror("Economizer Out Sensor Error"));
if(modbusr(c, 102 , bool), adderror("System Recoverable Protection"));
if(modbusr(c, 103 , bool), adderror("System Irrecoverable Protection"));
if(modbusr(c, 108 , bool), adderror("Flow Switch Protection"));
if(modbusr(c, 109 , bool), adderror("4-way valve error"));
if(modbusr(c, 128 , bool), adderror("DC Bus Low-voltage or Voltage Drop"));
if(modbusr(c, 129 , bool), adderror("DC Bus Over-voltage"));
if(modbusr(c, 129 , bool), adderror("DC Bus Over-voltage"));
if(modbusr(c, 130 , bool), adderror("AC Current Protection (Input Side)"));
if(modbusr(c, 131 , bool), adderror("IPM Error"));
if(modbusr(c, 132 , bool), adderror("PFC Error"));
if(modbusr(c, 133 , bool), adderror("Startup Error"));
if(modbusr(c, 134 , bool), adderror("Phase Loss"));
if(modbusr(c, 135 , bool), adderror("Drive Module Resetting"));
if(modbusr(c, 136 , bool), adderror("Compressor Overcurrent"));
if(modbusr(c, 137 , bool), adderror("Over-speed"));
if(modbusr(c, 138 , bool), adderror("Charging Circuit Error or Current Sensor Error"));
if(modbusr(c, 139 , bool), adderror("Desynchronizing"));
if(modbusr(c, 140 , bool), adderror("Compressor Stalling"));
if(modbusr(c, 141 , bool), adderror("Drive Communication Error"));
if(modbusr(c, 142 , bool), adderror("Radiator or IPM or PFC Over-temperature"));
if(modbusr(c, 143 , bool), adderror("Defective Radiator or IPM or PFC"));
if(modbusr(c, 146 , bool), adderror("Charging Circuit Error"));
if(modbusr(c, 147 , bool), adderror("AC Input Voltage Error"));
if(modbusr(c, 148 , bool), adderror("Drive Board Temp Sensor Error"));
if(modbusr(c, 149 , bool), adderror("AC Contactor Protection or Input Cross-zero Error"));
if(modbusr(c, 150 , bool), adderror("Temp Drift Protection"));
if(modbusr(c, 151 , bool), adderror("Sensor Connection Protection (Connection to Phase U or V failed)"));

Service Attributes

Compressor State

if(modbusr(c, 80, bool), "On", "Off")

Fan State

if(modbusr(c, 81, bool), "On", "Off")

4-way Valve State

if(modbusr(c, 83, bool), "On", "Off")

Compressor Crankcase Heater State

if(modbusr(c, 84, bool), "On", "Off")

Underpan Heater State

if(modbusr(c, 85, bool), "On", "Off")

Defrosting State

if(modbusr(c, 86, bool), "Defrosting", "End")

Oil Return State

if(modbusr(c, 87, bool), "In oil return", "No oil return")

T-discharge [°C]

MODBUSR(H, 119, Int16)/10

T-defrost [°C]

MODBUSR(H, 120, Int16)/10

T-suction [°C]

MODBUSR(H, 121, Int16)/10

T-economizer in [°C]

MODBUSR(H, 122, Int16)/10

T-economizer out [°C]

MODBUSR(H, 123, Int16)/10

Quiet Mode Switch

Reduces running noise via automatic compressor and fan speed control

Room Temperature Cooling Setpoint Thermostat

Room temperature target for cooling — active only when Control State is set to T-room (18–30°C)

Room Temperature Heating Setpoint Thermostat

Room temperature target for heating — active only when Control State is set to T-room (18–30°C)

Solar Heater Switch

Solar heater priority for energy conservation — warns if solar is not available

Service Attributes

Solar setting

Service Actions

Set Solar

Solar Heater

Read switch state

var ret := MODBUSR(C, 16, Bool);

if (ret, if ( !MODBUSR(C, 31, Bool), addwarning("Solar is not available")));

return(ret);

Write switch state

MODBUSW(C, 16, Bool, St)

Service Attributes

Solar setting

if(modbusr(C, 31, bool), "With", "Without")

Service Actions

Set Solar

Parameters: Solar

modbusw(C, 31, bool, S)

E-Heater Activation Temperature Thermostat

Outdoor temperature threshold for auxiliary electric heater activation (-20 to 18°C)

Gas Pipe Temperature Temperature Sensor Read-only

Refrigerant gas pipe (vapor line) temperature

Liquid Pipe Temperature Temperature Sensor Read-only

Refrigerant liquid pipe temperature

Optional Water Sensor Temperature Temperature Sensor Read-only

Outdoor Temperature Temperature Sensor Read-only

Remote Room Temperature Temperature Sensor Read-only

Remote room temperature sensor reading — warns if remote sensor is not available

Water Inlet Temperature (Plate Exchanger) Temperature Sensor Read-only

Water Outlet Temperature (Plate Exchanger) Temperature Sensor Read-only

Temperature Timer Switch

Thermostat Configuration Multi-value Switch

External thermostat connection type — Without, Air, or Air+Hot water

Values / States: Without · Air · Air + Hot water

Thermostat State Multi-value Switch Read-only

External thermostat demand status — Cool, Heat, or Off

Values / States: Cool · Heat · Off

Weather-Dependent Operation Switch

Automatic setpoint adjustment based on outdoor temperature using weather curves

Service Attributes

AT-Heat

AT-Cool

RT-Heat

RT-Cool

WT-Heat

WT-Cool

Weather-Dependent Operation

Read switch state

MODBUSR(C, 22, Bool)

Write switch state

MODBUSW(C, 22, Bool, St)

Service Attributes

AT-Heat

MODBUSR(H, 18, Int16) + " / " + MODBUSR(H, 17, uInt16)

AT-Cool

MODBUSR(H, 24, uInt16) + " / " + MODBUSR(H, 23, uInt16)

RT-Heat

MODBUSR(H, 20, uInt16) + " / " + MODBUSR(H, 19, uInt16)

RT-Cool

MODBUSR(H, 26, uInt16) + " / " + MODBUSR(H, 25, uInt16)

WT-Heat

MODBUSR(H, 22, uInt16) + " / " + MODBUSR(H, 21, uInt16)

WT-Cool

MODBUSR(H, 28, uInt16) + " / " + MODBUSR(H, 27, uInt16)

Weekly Timer Switch

Water Outlet Temperature Cooling Setpoint Thermostat

Water outlet temperature target for cooling — active when Control State is T-water out (7–25°C)

Water Outlet Temperature Heating Setpoint Thermostat

Water outlet temperature target for heating — active when Control State is T-water out (20–60°C)

Connection: Modbus RTU • 9600 baud• 8N1 • Slave ID: $[SlaveId]

Possible improvements (16)

C:11 Gate-Ctrl. — Gate card control — 0=Close, 1=Open. Hotel gate-card integration.
C:35 Refrigerant Recovery — 0=Off, 1=On. For service/maintenance — refrigerant recovery mode.
C:37 Cool 2-Way Valve — 0=Off, 1=On. Manual control of cooling 2-way valve.
H:117 Unit Status (as sensor) — Currently exposed as Outdoor Unit multi-value switch; could be a dedicated read-only sensor. Values: 01=Cool, 02=Heat, 06=Hot water, 08=Off.
H:133 T-floor debug — Current calculated floor debug temperature. Available as read-only sensor.
H:134 Debug time — Remaining floor debug time in hours.
H:136 Error Time for Floor Debug — Floor debug error timeout in seconds.
H:137 T-weather depend — Current calculated weather-dependent setpoint temperature.
H:142 Setting frequency — Compressor target frequency, 0–100 Hz.
H:143 Running frequency — Compressor actual running frequency, 0–100 Hz.
C:38 Heat 2-Way Valve — Read-only. 0=Off, 1=On. Heating 2-way valve state.
C:64 Comm Error IDU-Wired Controller — Read-only. 1=Error. Communication error between wired controller and indoor unit.
C:65 Comm Error ODU-Wired Controller — Read-only. 1=Error. Communication error between wired controller and outdoor unit.
C:66 Comm Error Drive-Wired Controller — Read-only. 1=Error. Communication error between wired controller and drive.
C:67 HP-Antifree — Read-only. 0=Off, 1=On. Heat pump antifreeze protection active.
C:152-191 Indoor Unit Sensor/State Coils — Various indoor unit sensor errors and component states (E-heater, water pump, valves, etc.). Partially covered by Hot Water Tank readscript (C:156) and Outdoor Unit readscript. Remaining: C:152 (condenser leaving water), C:153 (e-heater leaving water), C:154 (refrigerant liquid), C:155 (condenser entering water), C:158 (vapor line), C:160 (remote room — covered by Control State), C:169–C:191 (component states — partially covered by module service attributes).

Download Template

Sources

Sinclair S-Therm Modbus Protocol V15.2
2026-03-20
PDF
Sinclair S-Therm Ontario Monoblock Installation Manual
www.sinclair-solutions.com 2026-03-20
PDF