Awww man, why've you guys just let me spend £500 on an MFT when the FCU neon is all anyone ever needs. This place is really starting to get my back up, do you guys know anything about electrics?! :slapIt's fused from a wall switch that has a light on it, means its good.
Also, and this just might be me, but if both immersions went off at exactly the same time (which as I understand is the case here) I'd be inclined to think the problem was further back in the system. For example, if a room of 30 computers goes off at work, I wouldn't jump to the conclusion that 30 power supplies had all blown at the same time - I'd probably start at the breaker. In your case, I'd probably be investigating the controller if it controls both immersions.