Ariston Nuos Plus S2 Wi-Fi 250L Heat Pump Water Heater + Unvented Kit

Uses R290 natural refrigerant with a GWP of just 3 — over 470 times lower than the R134a used in the previous Nuos generation. The factory-sealed, pre-charged circuit means no on-site refrigerant handling and near-zero direct emissions over the product's lifetime, fully aligned with current and forthcoming F-Gas legislation.

At the EN 16147 standard test condition (7 °C air / 10 °C cold inlet / 55 °C set-point), the 250I achieves a COP of 3.51 — every unit of electricity delivers over 3.5 units of useful heat. Against the XL tapping profile, annual electricity consumption averages just 1,161.5 kWh/year under average climatic conditions.

The 0.65 m² lower heat-exchange coil accepts heat from a solar thermal array, gas or oil boiler, or solid fuel back-boiler. At 15 L/min primary flow, the coil delivers up to 9.76 kW — heating the full cylinder from 15 °C to 60 °C in under 59 minutes — enabling a true solar-plus-heat-pump hybrid system for maximum efficiency.

Integrated Wi-Fi gateway links to the Ariston Net app (iOS and Android) out of the box — no dongle or bridge required. Control temperature, set schedules, monitor energy consumption, activate Away mode, and receive system alerts remotely. Optional voice control via compatible smart-home platforms is supported.

Built-in SG1/SG2 Smart Grid signal inputs detect surplus solar generation and automatically switch the unit to a higher-output heating mode — maximising PV self-consumption without a separate diverter device. The PV boost temperature is fully configurable by the installer via the PV SET parameter.

The S2 generation operates at just 48 dB(A) (EN 12102-2, ducted Ø200) — measurably quieter than its predecessor. An optional Night function drops fan speed further for whisper-quiet overnight operation, making the unit suitable for installations in or adjacent to habitable rooms.

Includes Green, Green+, Boost, Comfort, i-Memory (learns four weeks of demand patterns and schedules accordingly), daily and weekly programme schedules, Anti-Legionella automatic thermal sanitisation, and Voyage (holiday away mode with timed reactivation) — all accessible from the touch display or the app.

The 245-litre steel cylinder is protected by Titanshield anti-corrosion enamel and a replaceable sacrificial magnesium anode accessible via a dedicated service flange without draining the tank. Outer insulation is 50 mm polyurethane — CFC and HCFC free — covered in a galvanised pre-painted steel jacket.

A hot-gas defrost valve allows uninterrupted heat pump operation down to -10 C ambient by preventing condenser condensate from freezing — extending the hours each year the compressor runs rather than the element. At higher ambients (up to +42 C) efficiency improves further, reducing running costs in warmer seasons.

Equipped with Ariston BusBridgeNet connectivity. Connects to a Sensys HD remote control and other BusBridgeNet-compatible Ariston products — boilers, heating heat pumps, solar controllers — on a shared bus. A single Ariston Net Wi-Fi gateway on the bus manages heating and domestic hot water from one app across the whole system.

The MPN 4057139 bundle includes a complete G3-compliant unvented safety assembly — pressure reducing valve, expansion vessel, TPRV, combination PRV, and tundish — correctly rated for this 245-litre cylinder. This reduces installer procurement time and ensures all safety components are factory-matched to the unit.

Accepts 150, 160, or 200 mm duct on both inlet and exhaust, with 189 Pa available static pressure for extended duct runs to an external wall or adjacent space. Operates without ducting in rooms of at least 20 m³. Ships lying flat with built-in carry straps for safe internal manoeuvring, and has adjustable levelling feet.