Thanks LR.
Looking on the net at various sites, I reckon it's a gonner. I've tried some gentle heat (45C) in the oven and a long suck but looks like I'll need a replacement.
From a few sites HTC seem particularly vulnerable to water damage to the extent that there is a built in tell-tale for dampness. No hope of guarantee then.
I've ordered the tool set, out of interest, Just looked, new TC One Max is +/- €700 here
. On the bright side I might make something selling the dud on Fleabay.
BTW It was vibrating and flashed a couple of times when I took it out so guess it had powered up in the washer.