I like closure.
History : I opened this thread 9 months ago, bought a new level sensor but the light stopped gflashing before I replaced.
Well it started again - I went to th shed, dug out the replacement I had bought and Bobs your uncle.
No more flashing light

Thanks for all your help with this one guys. I know its been a while but life has been in the fast lane recently.
Just wanted to finish this post. I hate unanswered threads!!