Onyx Direct Stainless Steel Unvented Cylinder
The Onyx Direct Stainless Steel Unvented Cylinder is a fully electric hot water solution designed for homes and apartments that aren’t connected to a traditional boiler system. Featuring two powerful 3kW immersion heaters — one for day-to-day timed use and another as a backup — it ensures reliable and efficient hot water whenever you need it. From 170L upwards, the primary immersion heater is upgraded with a Smart Eco thermostat, helping to maintain consistent temperatures while keeping energy use low.
Built in the UK and made from high-grade Duplex stainless steel, the Onyx Direct Cylinder offers exceptional durability and corrosion resistance. It’s engineered to deliver strong, dependable performance for all-electric properties, making it a perfect choice for modern households, rental apartments and energy-efficient installations.
Complete G3-Approved Kit Included
Each cylinder comes with a full G3 unvented installation kit, including:
Two Thermowatt 3kW immersion heaters
(On 170L, 200L, 250L and 300L models, the second immersion is a Smart Immersion)
Zilmet expansion vessel
Caleffi tundish
Caleffi 22mm inlet control group with pressure relief valve
Factory-fitted Caleffi 7-bar / 90°C temperature & pressure relief valve
Factory-fitted secondary return (supplied with 200L, 250L and 300L models)
Available in a wide range of sizes — 90L, 125L, 150L, 170L, 200L, 250L and 300L, there's an option to suit everything from compact apartments to larger homes with higher hot water demand.
FAQs
Is this cylinder suitable for homes without a boiler?
Yes — this is a **direct** cylinder, meaning it heats water using immersion heaters only, making it ideal for 100% electric properties.
What is the Smart Eco immersion heater?
On models 170L and above, the main immersion heater includes a Smart Eco thermostat that learns usage patterns and heats water more efficiently.
Does the cylinder come with everything needed for installation?
Absolutely. The Onyx Direct cylinder includes a full G3 unvented kit with all essential safety and control components.
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