As per title it's a small office with no air circulation....the old router is dead and it's because of overheating I suspect.
It was a budget router and only for one user (without a cooling fan0.....I suspect it will probably be a home/ small office router within a budget price range of 30 euro (34 US Dollars) or so.....typically, these devices do not appear to have fans no matter what manufacturer....
Is the best solution to install a small "desk type fan" beside the router to blow air over the vent holes? It's not the most elegant solution so i'm looking for other ideas....thanks.