Heater not working

Hi Guys,
I have a GU 4.8 on dual fuel and just wondering if anyone out there has had any probs with the heater not working real well. I've heard a few ideas on why it's not working and a mechanic said he is 90% sure its the heater core. Is it possible that the LPG system is affecting it? Also what sort of money would it cost to get it done, as I couldnt do it myself.

Thanks in advance :)

Tobes

check your heater hoses for blockage and the controll valve on the fire wall where the hoses go to
see if it is working
cable from controll pannel leaver could have slipped

Your heater core may be blocked with "mud"
and x2 make sure lever opens all the way.

to un block the core insert hose it will come out like tooth paste being nice about it lol

Wrong post...

Thanks guys :) i'll have a look.
I had all the cooling system done a while ago, new hoses and radiator and there's no mud or anything in it, the coolent has stayed nice n green, or are they not connected to each other?
Thanks for all your help