try a new primary NTC
https://www.ebay.co.uk/itm/Baxi-Tem...224440?hash=item4d468e7ab8:g:nioAAOSwKJtaoRJJ
https://www.ebay.co.uk/itm/Baxi-Tem...224440?hash=item4d468e7ab8:g:nioAAOSwKJtaoRJJ
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