Special Offers ONYX 12L Red Heating Vessel ONYX12LHEAT

The ONYX 12L Red Heating Vessel is a diaphragm expansion vessel for sealed heating systems, supplied within the Special Offers range of pressure vessels and accessories. It absorbs the expansion of heated water in a closed circuit, limiting pressure rise and protecting the boiler and system components. The red casing identifies it as a heating-side vessel rather than a potable hot water unit.

• Water weeping from the Schrader valve or valve cap, indicating a failed diaphragm
• System pressure rising sharply when the boiler heats up and falling again as it cools
• Frequent topping up of system pressure, or the filling loop left open to compensate
• Boiler locking out on low pressure or a pressure gauge reading that will not hold
• Visible corrosion, pitting or damp patches on the vessel shell or connection

• Confirm the required vessel volume for the system and match it to the 12 litre capacity
• Check the connection size and thread on the existing vessel against the 3/4 connection
• Verify the pre-charge pressure is suitable for the system's cold fill pressure
• Check the available space and mounting arrangement before removing the old vessel