APOLLO Wi-Fi Boiler Aquastat

An aquastat is essentially a thermostat for water: instead of sensing room air, it senses the boiler's water temperature and switches heating equipment to keep that water in the right range. When the water drops below the setpoint, the aquastat closes its relay to call the burner or circulator; when the water reaches temperature, it opens the relay again. The APOLLO Wi-Fi Boiler Aquastat is a digital aquastat for boiler supply-temperature control, with a selectable internal or external boiler sensor, a 3.5-inch color touchscreen showing the live water temperature, and Wi-Fi app monitoring on top.

An aquastat controls water temperature at the boiler; a boiler thermostat controls room air temperature and tells the boiler when the living space needs heat. Most hydronic systems use both: the aquastat keeps the boiler water in its operating range, and the room thermostat calls for heat when the house cools down. If you need to regulate the water temperature your boiler produces, this aquastat is the right model. If you need room-temperature control and a remote panel for your boiler, see the APOLLO Wi-Fi Boiler Thermostat — selectable from the model dropdown at the top of this page.

In many installations, yes. The APOLLO provides a 5A SPST-NO relay with COM/NO/NC terminals — the same dry-contact switching used by conventional immersion and strap-on aquastats to call a circulator, burner control, or motorized valve. Because it accepts both 12–24VAC/DC and 110–240VAC supply power, it fits most boiler-room wiring without an added transformer. It is a temperature controller, not a safety device: keep your boiler's factory high-limit safety control in place and let the APOLLO handle operating control. Compare your existing aquastat's wiring against the diagram in the product manual before ordering.

Yes. Wood boilers are one of the most common applications for an external aquastat: the sensor reads the boiler or storage-tank water temperature and the relay switches the circulator that moves heat to the house, or other equipment that accepts a dry-contact call. The Wi-Fi app is especially useful here — you can watch the water temperature from the house and know when the fire needs tending without walking out to the boiler. MBTEK carries a full line of indoor wood gasification boilers that pair with this aquastat for circulator and zone control.

Wiring involves three connections: supply power (12–24VAC/DC or 110–240VAC to the power terminals), the boiler sensor (internal, or the external sensor input for a strap-on or well-mounted probe at the boiler), and the relay output (COM and NO/NC contacts to the circulator, burner control circuit, or valve you want switched). The full wiring diagram is in the APOLLO manual, downloadable in the documents section of this page. If you are switching line-voltage loads or working inside boiler control circuits, have a licensed electrician or heating technician make the connections.

An operating aquastat works around a target water temperature and a differential — the swing between where the relay closes and where it opens, which prevents short cycling. On the APOLLO you set the target water temperature directly on the touchscreen or in the app, and scheduling lets you run different water setpoints by time of day using 5/2, 7-day, or 24-hour programs. Your boiler's own high-limit safety control remains the independent upper cutoff, as required for safe operation.

Yes. The APOLLO connects to a 2.4GHz network using IEEE 802.11 b/g/n with WPA/WPA2 security, and the companion app shows the live boiler water temperature, lets you change the setpoint, and manages schedules remotely. For building management and automation systems it also supports wired BACnet MSTP, BACnet/IP, and MQTT, plus Google Home monitoring — connectivity that conventional mechanical aquastats simply don't offer.

The output is a 5 Amp maximum SPST relay with COM, NO, and NC terminals. That rating covers the typical calls in a boiler room: a circulator pump, a zone valve or motorized valve actuator, a burner control circuit, or the low-voltage enable input on other heating equipment. Loads above 5A — large pumps or resistive elements — should be switched through a contactor or relay rated for the load, with the APOLLO driving the contactor coil. The boiler aquastat is part of the APOLLO Wi-Fi thermostat platform, which also includes dedicated models for boiler room-thermostat control, fan coil units, radiant floor heating, pool and spa aquastat control, snow melt systems, and electric baseboard heaters.