tom tom one xl problems

Hi, I have a TomTom one xl, bought for me as a present in september when i started a new job as a van driver.
it has always played up intermittently and I have reset many times and done lots of updates but the problem remains.
you are driving along and all is well, tom tom is telling you the directions and the arrow is showing corectly, then the blue arrow icon (my vehicle) moves about half an inch off the road and appears to be attached by a string to the correct position. Obviously then tom tom tells me to turn left or right depending, which is a bit worrying when travelling on a motorway.
Today it did the ultimate, I was driving on the A46 near to coventry when it happened and on the screen i was driving through a lake, now I know it was spitting with rain but this was too far.
I think it is time to get tomtom sorted out and need to know what is the best way to do this, I need satnav for my job now and cant be without it for any time, also i dont know if I have a receipt or if it is registered, however it is all set up to update so I assume all should be ok,
can anyone point me in the right direction please, i was told tomtom was the best of the satnavs but have to admit I am unsure if this is correct.

thanks

[getsurfers]

Does that van have a heated or UV coated screen by any chance? Which van?

Where do you locate the Tomtom in the van?

no i dont think the screen is treated in any way,it is an LDV Maxus.

i put tomtom on the windscreen, right bottom corner and it is in the standard suction holder. it works fine for a day or two then goes on a wobbler, i cant put up with it much longer. the whole point is it is supposed to get me where i have to go without stress, i am more stressed wondering when it will let me down again, usually when i am in an unknown city just as i hit the one way system.

[getsurfers]

Try it in the middle of the screen.

If the screen (when looking at the vehicle) looks yellowish or purple when light bounces on it (like Renaults, Vauxhalls etc) then you have a coated screen - which can affect GPS.

I suspect being in the corner you're getting a signal bounce inside the vehicle. They cope with signal bounce from buildings, but if the signal is bounced again they go mental. When I had a Transit connect as a company vehicle, mine would only work well in the center of the screen due to signal bounce and the heated screen.

If you still have issue, then you may have an issue. But as the device can use over 12 sats to establish your location, it should self calibrate your true location. So I doubt it's a device issue.

You may have to use an external aerial for the tomtom.

cheers for that i will give it a go next week when out and about, I havent even thought about an external aerial, I will also look into that.

very good of you to help, thanks