problems with glowworm boiler?

I have a sealed central heating system.Some where along the line i seem to be loosing a lot of water,i keep having to top the system up every day from the pressure bottle.The radiator in the bathroom gets air in it all the time,have to bleed it quite often.Also get gurgling inside the boiler and pilot light also goes out now and again,cannot see any leaks any where.Have seen water coming out of the expansion pipe before,could it be anything to do with the pressure relief valve!