How do I get my space heater to work. Andrews G80 DV?

I have a Andrews G80 DV gas space heater, I bought it off Ebay and was told it was about 6 months old and had been used very little, but it was too big for the building it was in so the person down sized.
It came with no gas pipe and regulator so I purchased a pipe and regulator (low pressure).
My problem is that it won't light unless I have the top cover off the heater ,you have to turn the fan on first then hold in the gas button, and then press the igniter button but as soon as you let go of the gas button the flame goes out. Can anyone help or give me the phone number of someone who can, I live in Pontefract West Yorks my phone number is 07787950446. thanks.