Hello @km1967 Error B7 indicates a problem with the coding plug (part number 7863506, type 2A03:0203). You can start by cleaning the contacts on the coding plug. To do this, you need to turn off the main switch, remove the front cover and the boiler control unit cover, pull out the coding plug, and clean the contacts. If this does not resolve the issue, the coding plug (order number 7863506) will need to be replaced. If the system pressure continues to fluctuate, the expansion vessel should also be checked. Best regards
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