warning light glowplug/coil keeps coming on kangoo 1.5 dci?

i have taken my van to the garage 3 times in the last fortnight .i had problems starting the van and a loss of power the first trip to the garage the guys cleaned the egr valve a week later the light came on, back to the garage the guys changed all the glowplugs .a week later the light was on again back to the garage the guys changed the camshaft position sensor today the light is back on so it will be going back to the garage on tuesday morning.any ideas