SONOFF Thermostat Core: underfloor heating and boiler thermostat – wiring and guide

SONOFF Thermostat Core (TP-WGZBA) is an in-wall Zigbee thermostat that controls hydronic underfloor heating and a boiler from a single device. It has a rotary dial, a display that wakes up only when you walk up to it, three weekly schedules, and it can work together with TRV-ZBT Gen2 radiator valves. This guide shows whether it suits your heating, how to wire it, what else you need and how to set it up so it really saves energy.

What is SONOFF Thermostat Core

Thermostat Core (model TP-WGZBA) is a room thermostat for a standard wall box. It measures the room temperature and switches the heating on and off accordingly. Unlike typical room thermostats, it has two separate outputs:

• an active relay (100 to 240 V AC, max. 3 A) for thermoelectric actuators of hydronic underfloor heating,
• a potential-free COM/NO contact that tells the boiler “heat” or “stop”, just like a classic room thermostat.

You control it with a physical rotary dial from 5 to 30 °C, not with tiny touch arrows. A built-in radar sensor turns the display on when you approach and off when you leave, so it does not glow in the bedroom at night. Schedules, temperature offset and other settings are done in the eWeLink app via a Zigbee gateway.

SONOFF Thermostat CoreZigbee thermostat for underfloor heating and boilers.€34.99 SONOFF Zigbee Bridge ProThe most affordable gateway for the thermostat, valves and sensors.€17.79 SONOFF TRV-ZBT Gen2Radiator valve the thermostat can control.€29.50

Does Thermostat Core suit your heating?

What you need

The thermostat communicates over Zigbee 3.0, so it needs a Zigbee gateway for app control and app schedules. Without a gateway it works as a plain thermostat with a dial.

Thermostatmeasures temperature, switches underfloor heating and boiler

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Zigbee gatewayBridge Pro, Bridge Ultra, NSPanel Pro, iHost

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PhoneeWeLink, Home Assistant, Apple Home

Schedules are stored in the thermostat itself. If the internet or the gateway goes down, it keeps heating according to schedule.

Thermostat Core is a new device, so the gateway must run current firmware. Minimum versions according to the manufacturer:

You will also need:

• a wall box with live (L) and neutral (N); the thermostat measures 86 × 86 mm, has 60 mm screw spacing and sits 31.5 mm into the wall,
• wires to the actuators or the boiler (terminals accept 0.2 to 3.5 mm²),
• optionally a floor probe NTC 10 kΩ (B3950) that protects the floor from overheating; not included,
• optionally a Zigbee thermometer for the room and a window sensor (see features).

Wiring the thermostat for underfloor heating and a boiler

There are seven numbered terminals on the back. Which ones you use depends on whether you control underfloor heating, a boiler or both.

1. Switch off the breaker for the circuit feeding the box and check with a tester that the wires are dead.
2. Remove the old thermostat and see which wires are in the box. You need live L and neutral N. If there are only two wires to the boiler, the thermostat cannot be connected without adding power wires.
3. Connect power: N to terminal 1, L to terminal 2.
4. Underfloor heating: connect the actuators’ live wire to terminal 3 (L Out) and their neutral to N. Wire several actuators of one zone in parallel and make sure they stay below 3 A in total.
5. Boiler: connect the two wires of the boiler’s room thermostat input to terminals 4 (COM) and 5 (NO). The boiler must accept simple ON/OFF control.
6. Floor probe (if used) goes to terminals 6 and 7. Place it in a protective conduit in the floor between the heating loops.
7. Screw the mounting frame to the box, attach the thermostat and only then switch the breaker back on.

Italian 503 box (rectangular): the thermostat has an 86 mm square format, so a 503 box needs an adapter. SONOFF offers a 3D-print file for it on its website; you will also need two M3 brass heat-set inserts and two M3 × 10 mm screws.

Pairing and first setup

1. Update the gateway and the eWeLink app to the versions in the table above.
2. In eWeLink open your Zigbee gateway, tap Add and put the thermostat into pairing mode as described in the quick guide in the box. Keep it within a few metres of the gateway for the first pairing.
3. After adding it, check for a thermostat firmware update. The manufacturer recommends version 1.0.3 or later.
4. In Heating System Settings set the actuator type and boiler contact type. The default logic is NO: the relay closes when heat is needed. That matches common NC actuators (closed when unpowered) and common boilers. For NO actuators choose “NO actuator”, for a boiler with a break contact choose “NC boiler”.
5. Set the hysteresis, i.e. how far the temperature must drop below target before heating restarts. A wider hysteresis means less boiler cycling but larger temperature swings.
6. Create a heating schedule and switch the thermostat to automatic mode.

Features that save energy

Modes and temporary changes

Automatic mode follows the schedule. Manual holds the temperature set with the dial. Off is actually anti-freeze mode: heating stops but the thermostat protects the room from freezing. Double-press the button to switch to automatic mode. The app also offers two temporary modes, Boost and Timer, for a short heat-up without changing the schedule.

Three weekly schedules

The thermostat has three independent weekly schedules, each with up to 12 time periods per day: one for a normal week, one for working from home and one for holidays. Schedules run on the built-in real-time clock in the thermostat, so they work without internet and without the gateway as long as the thermostat has power.

Underfloor heating reacts slowly: the floor takes hours to warm up and cool down. Start setbacks 1 to 2 hours before you leave and morning heat-up before you get up. A deep night setback does not pay off with underfloor heating; 1 to 2 °C is enough.

Radar display and occupancy heating

The radar presence sensor turns the display on when you come closer. Sensitivity has three levels: about 0.3 m, 0.6 m and 1 m. The same sensor can drive occupancy-based heating: it heats when someone is in the room and stops when it is empty. Useful for a home office or guest room.

Accurate temperature: external thermometer and offset

A wall thermostat measures a temperature affected by the wall and its own electronics. You can set a temperature offset or use a Zigbee thermometer placed elsewhere in the room as the temperature source. Supported models are SNZB-02, SNZB-02P, SNZB-02D, SNZB-02WD, SNZB-02LD, SNZB-02B and SNZB-02M. The thermometer must be connected to the same gateway.

Open window detection

When you air the room, the thermostat detects it from a sharp temperature drop or from a Zigbee window sensor (SNZB-04, SNZB-04P, SNZB-04PR2) on the same gateway. Heating then switches to anti-freeze mode. With underfloor heating the saving is smaller than with radiators (the floor keeps radiating), but with a boiler and radiators it pays off.

Protection and overview

• Floor probe watches the floor temperature, overheat protection turns heating off.
• Anti-freeze protection keeps a minimum temperature even when off.
• Child lock prevents unwanted changes with the dial.
• Up to 6 months of history: target and actual temperature and heating time in eWeLink.

Working with TRV-ZBT Gen2 valves

If you have radiators with SONOFF TRV-ZBT Gen2 valves, Thermostat Core can act as their control panel: via a compatible gateway it synchronises target temperature, mode and schedule for up to 5 TRV-ZBT Gen2 valves. Turn the dial on the wall and the valves in the room follow. In the app this appears as Thermostat Panel Control; Bridge Pro needs firmware 3.5.0 and NSPanel Pro 4.9.0 for it.

Important: synchronisation does not turn each valve into a separate heat request for the boiler. The thermostat switches the boiler based on the temperature in its own room. If you want the boiler to start whenever any room calls for heat, you need a separate control setup, for example an automation in Home Assistant. The older TRVZB (Gen1) is not listed by the manufacturer for this feature.

Home Assistant, Apple Home and other systems

In Zigbee2MQTT you pair the thermostat like any Zigbee device (Permit join). Check your Zigbee2MQTT version first, older versions may not recognise it correctly. To get started, see Getting started with Home Assistant.

Ready-made bundles with prices

Prices load directly from the shop, so you always see the current price and stock.

Underfloor heating, one zone

Thermostat for the manifold actuators, app control and a window sensor.

• SONOFF Zigbee Bridge Pro€17.79
• SONOFF Thermostat Core€34.99
• SNZB-04PR2 window sensor€11.49

Total €64.27

Boiler and three radiators

The thermostat switches the boiler, TRV-ZBT Gen2 valves follow its temperature and schedule.

• SONOFF Zigbee Bridge Pro€17.79
• SONOFF Thermostat Core€34.99
• 3× SONOFF TRV-ZBT Gen2€88.50

Total €141.28

When something does not work

• Heating does not turn on: check that the target is above the measured temperature, the hysteresis setting, the actuator and boiler type (NO/NC) and the wiring. Also make sure the actuators are 230 V, not 24 V.
• Heating does not turn off: check the temperature reading (offset, external thermometer) and the NO/NC setting. If the actuator or boiler stays on even with the contact open, the fault is outside the thermostat.
• It works in reverse (heats when warm, does not heat when cold): almost always the wrong actuator or boiler contact type. Switch NO/NC in Heating System Settings.
• The thermostat will not pair: update the gateway firmware, bring the thermostat closer and check that Zigbee2MQTT is 2.14.0 or later.
• Zigbee or internet outage: nothing happens, schedules keep running in the thermostat. You just cannot change them from your phone for a while.

Frequently asked questions