This is a new problem in connection with water, as these units are very well sealed, so I'm wondering if the deep puddles and the fault are just a coincidence.
There's a well known problem of a failure in the mainboard electronics which cuts out the normal mode leaving only Eco power in both switch positions, and this sounds very much like that. Unfortunately it's unrepairable if so, leaving only the new unit option.
You need to be careful in buying a unit elsewhere. A large batch of bikes were made with this fault at point of manufacture, and they were sent out to dealers with new units and instructions to swap then over and scrap the old ones since Giant had no repair facility. Not all of the old units were scrapped and they still surface sometimes. I've learnt of two more recently, the last only this morning in Cornwall.
It's very much personal choice on replacing a unit, that £400 sounding a very low quote as it's usually £450 or £500 fitted. Personally I'd be inclined to upgrade to one of the newer models with triple power mode and very long range battery like the Kalkhoffs as they are so much more capable and do away with the odd weaknesses that the old bikes had. But of course that's a big expenditure.
If you are convinced the damp is connected with the problem, keeping the bike in the dry will dry out the connectors over time, especially if you could get it into a room with some warmth. There's no chance of water getting into the unit though, it's too well sealed with face sealed bearings in neoprene sealing rings, multi ribbed tight fitting cable grommets etc.
Heres the link to the switch start point for checking that Paul mentions:
Lafree Repair
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