A week ago I was deleting some rules in the 'find and merge contacts' page, and it appears to have deleted the entire block of household rules, so that there is no way I can add new household rules, and adding new households does not work due to no rules existing. The individual and organisation blocks are both there, but not the household one. How can I get this back?
If you have access to your db you might need to check the table civicrm_dedupe_rule_group. If indeed you deleted the rows for Household, then you might be able to reinsert them there. I would suggest testing on a dev site if you have one.
These are the two rows I see
id contact_type threshold used name title is_reserved
3 Household 10 Supervised HouseholdSupervised Name and Email 0
6 Household 10 Unsupervised HouseholdUnsupervised Name and Email 0