Onyx Indirect Stainless Steel Unvented Cylinder
The Onyx Indirect Stainless Steel Unvented Cylinder is designed for homes and properties that use a gas, oil or biomass boiler as their main heat source. With a built-in high-performance internal coil, it reheats quickly and delivers strong, reliable hot water across the home. For added reassurance, each model also includes a 3kW immersion heater that acts as a backup should the boiler ever be offline.
Manufactured in the UK from premium Duplex stainless steel, the Onyx Indirect range offers exceptional strength, corrosion resistance and long-term durability. Whether installed in a family home, rental property or light commercial setting, it provides fast recovery times and consistent hot water performance. Available in sizes from 90L to 300L, it’s suitable for small apartments right up to larger households with multiple bathrooms.
Complete G3-Approved Kit Included
Every cylinder comes with a full G3-compliant installation kit, featuring:
Thermowatt 3kW immersion heater
Zilmet expansion vessel
Caleffi tundish
Caleffi 22mm inlet control group with PRV
Intatec dual control thermostat
Honeywell Home 22mm 2-port motorised zone valve
Factory-fitted Caleffi 7 bar / 90°C temperature & pressure relief valve
Factory-fitted secondary return (included with 200L, 250L and 300L models)
Available sizes: 90L, 125L, 150L, 170L, 200L, 250L, 300L
FAQs
Is an indirect cylinder suitable for my home?
Yes — indirect cylinders are ideal if you already have a boiler. They heat water via an internal coil, providing quicker recovery and better efficiency than direct-only systems.
Does the cylinder still work if the boiler stops working?
Absolutely. The built-in 3kW immersion heater provides backup heating, ensuring you’re never without hot water.
Is this cylinder suitable for larger homes?
Yes — with models up to 300L and fast reheat times, the Onyx Indirect range can comfortably support properties with multiple bathrooms.
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