my boiler pressure has dropped to 0.4 and is flashing = no heating?

You need to find the filling loop - thats the valve that allows fresh water from the main into your boiler, increasing the pressure. Open the tap on the loop, and watch the pressure rise. You don't say what make of boiler you have - some filling loops are a flexible steel braided pipe with a tap on - some newer boilers have a plastic tap inside the casing.

John
April 2008