I rang Rogers Space Heaters today and a very helpful chap there is able to supply me with the over heat stat. Its in the post so I will report back when it is fitted. He said that they should be closed at rest, so confirmed what we had found. They are only the other side of Bodmin Moor to me, but at £2.99 postage it wasnt worth me driving over. Good to know where they are though for any bigger problems/more expensive parts.