This yellow unit is making a really loud buzzing noise (and feels hot!), but no one knows what it is, or its function, and the manufacturer no longer has it in their range or can tell me about it, so I can't attempt to find an alternative!
The hot water can be heated by an immersion heater, or indirectly by the pellet boiler. This unit is on the outlet from the cylinder back to the boiler. The installation is 6 years old (and the installers went bust 3 years ago)
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