Viessmann 100 WB1C Combi Plate Heat Exchanger 7828746

The Viessmann 7828746 is a 20-plate heat exchanger used on Vitodens 100 combi boilers. It is the domestic hot water plate stack, transferring heat from the primary circuit into the mains cold water supply as it passes through the boiler. The plate pack is built from stainless steel plates brazed into a single sealed unit, with tappings for the primary and DHW connections.

• Domestic hot water runs hot then cold, or the temperature at the tap fluctuates while the boiler stays in heating mode.
• Hot water flow rate drops noticeably compared with the cold supply, particularly in hard water areas.
• The plate stack weeps or drips at the gasket faces or between plates.
• Heating works normally but the hot water outlet stays cool, pointing to a blocked or scaled secondary side.
• Sludge or scale debris is found when the DHW circuit is flushed.

• This part is fitted to a gas appliance; installation must be carried out by a Gas Safe registered engineer.
• Confirm the boiler model and serial number against the compatibility list, as plate count and connection layout vary across Vitodens variants.
• Check the existing plate stack for the number of plates before ordering, and confirm whether the O-rings on the appliance are reusable.
• Decide between the refurbished and brand new options before adding to the basket.