Ok, this is probably a strange one!

I've been having trouble with the temperature selector knob on my washing
machine sticking, it's now freed itself but it does seem a bit loose, so I
have no idea if the knob is actually connected to anything!

So I'd like to actually test the temperature of the water in wash
independantly. Ideally some sort of device which could survive a wash cycle
then tell me what the max temp was during it, but I'm thinking they probably
don't exist?!

Does anyone have any ideas?