I am not sure that you are able to do it the exact way you mentioned. The problem you would run into would be that your criteria on the action rule would have to be matching two separate requests types - which can never work because no single ticket can have 2 request types. Your rule triggering would be based on the ticket creation of Request Type A, but your criteria would have to match both A and B AND the custom field which I don't think would work. You could make so that it matches "any" of those 3, but then it's sending an email every-time any of those 3 events happens individually, regardless of whether the custom field in Request B is set to no.
I've looked through the action rules and I can't find anything that makes sense. Because what your wanting is based on "inaction" on the part of the technician, I don't believe action rules would work for this. Perhaps someone else would know how to get those to work though.
Have you already looked through the Priority Types and Alerts options? It looks like you can schedule certain alert emails to be sent every day when an update hasn't happened or after a due date has been missed. I believe you can't base it on the content of custom fields, though.
Hope that helps!
I looked at the priority and alerts, but I don't think it would be selective enough on the email recipient.
I think I'm just trying to do something that's not possible within Webhelpdesk at the moment.
I'll have to keep with the manual method of poking them with a stick for the moment