I have an ideal standard he30 boiler instaled about 6 weeks ago. the boiler keeps losing presure about half a bar every 2 days if i dont top it up it will trip the fuse on the fuse board acording to the ideal instruction manual it should put up a fault code and not fire up. i have had the instaler out about 6 times and they say there must be a leak but nothing obviouse. but the boiler is fine. so i asked why it trips the fuse when the presure is low. the reply was that the boiler keeps fireing even if the presure is low and overheats the pump which trips the fuse. i said that isnt what the manufacters instructions said and i was told this is normal for these boilers. is this true evan if the instructions say other wise?

All the combis I've come across merely fail to fire if the pressure is not up. not only do they not fire, nothing else works including the pump and in any event the pump should not overheat just on low pressure.
water loss - try turning off the valves on the flow & return pipes [3/4 inch ones] 1 valve per pipe . This will isolate the rest of the system - rads etc Note pressure over a time period. In this mode the hot water circuit will still work but do NOT use the heating circuit
1/2 bar over 2 days is not serious but it should be found
Once you have either mended the leak in the rest of the system or found there is not one, insist on a replacement boiler
In any event having looked at the reasons given for the fuse blowing, I would definitely get a replacement.
These problems should not happen on a new boiler
I list Worcester.-Ariston-GlowWorm-Ideal- and many others who would confirm this