The problem is the rule needs to be set on one of the fields inside the repeating section and I'm not being given the option when I select the Condition field of specifying "All occurrences of <field>". I have found a solution, but I'm not sure it's the best solution. I have created a field on a hidden view and used it to do the checking...
Rule on TriggerValue - Condition: None - This rule always applies Action: Set the value of CheckingField = concat(CheckingField, "1") - this just triggers the rules on CheckingField any time the value of TriggerValue is changed
2 Rules on CheckingField - (1) Condition: All occurrences of TriggerField != 'Yes' Action: Set the value of ResultValue = 'No' (2) Condition: Any occurrence of TriggerField = 'Yes' Action: Set the value of ResultValue = 'Yes'
This works correctly, but I'd be interested to know if there's a simpler solution.