Gas air heater installation

[dorisrob]

Hi I have a gas air heater for the van.
I have had the van since new for about 10 months, but have not used the gas heater because we live in Nth Qld.
I have travelled down to Brisbane and tried it out and it seems to have problem. It starts ok on setting 5 (highest) but does not seem to regulate the temp. That is, the thermostat does not seem to be working.
I had it working on 5 for 1.5 hrs and then turned it down to level 3, the heater fan stopped, and after about an hour the van was cold inside again but the heater just shut down.
Do you have any ideas.

Rob