...I went to check the levels etc today and found I could not remove the top from the tank - it will turn about an inch then hits a solid 'stop' and nothing but nothing will make it 'pass' this point - any ideas please:idea:
Have you pressed firmly downwards as you turn the cap?
I have met similarly difficult caps, usualy the rubber washer on the caps sealing face / safety valve has seen better days becoming swollen, slightly soft and willing to migrate round the edge of the brass washer that pushes it down. It then jams the cap up by leaving insufficent clearance for the cap to clear the baynet catches around the outside of the cap and filler neck. There are two sets of bayonet on the filler, one to hold it sealed fully home and a safety catch to help prevent massive water loss when/if the cap is opened hot.
You may need to press hard.