I'm not sure what the legal aspect would be but Baxi may approve an external expansion vessel fitted to the cold inlet...and then add some sort of filter unit to collect the old baffle debris. Something like a polypropylene cartridge type device.
Thanks GasGuru and BlueLoo both - much appreciated. I should point out that I'm not a plumber, I'm only the householder so deffo won't be doing any of that myself, but I see where you're coming from. Currently trying to get hold of Heatrae Sadia to see what they've got to say for themselves.
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