Hi Jennie,

With regards to (over) filling your heater, you need to fill it up carefully, then get a cheap measuring jug ( mine cost 40p ) empty the contents of the heater into it and note how much it has taken to fill it.

If you then use the jug every time you fill it, you can put just the right amount in knowing that you won't overfill it.

NB: for this to work, you have to let it burn out each time of course.

Darren.