pump not working

Hi, I have just come back from holiday to find that, when i switched the central heating/ hot water back on, that my power shower doesn't work. It has next to no pressure and i can't hear the pump actually firing up. I usually have to place the shower head in the bath to prime the tank and then once the pump makes a higher pitched sound then it is fully primed. Now it just dribbles hot water without any noise.
As i have just moved into this house 4 months ago i don't know how or when it was installed.
Any ideas on how to fix this?
cheers

You haven't got enough head of water to push the air out of the pipe and create a flow to turn the pump on. (Should have been a Negative Head pump really). While you've been away the air has settled.

I'd use an aquavac to suck the water through the hose and pipes, but if I was feeling lazy I'd remove the shower head and suck on the hose!

thanks for the tip. I have tried to suck the air our myself. Not the nicest experience for a monday morning, but i dont know where to get a suction pump from. How long do i do this for?? It doesnt seem to be working yet.