Hi Danny, If you have to top up your sealed system regularly as you suggest, you have a much more serious problem than just getting the boiler to start. Regular topping up, means a continous leak in your system somewhere, and all the fresh water you introduce into the system during the top up means that you no longer have a sealed system. This means that all your radiators and boiler will rust away very much faster, possibly within ten years or even three. Your first priority should be to get the leak fixed.
NORMAN GRAHAM
August 2008