Check the batteries - the vast majority of issues actually come down to the batteries. Firstly, most portable units require batteries to ignite the unit. We have seen people not put the batteries in, put batteries in wrong, or, simply the batteries die and they haven't changed them - so the first thing to do is ensure some new, good batteries are correctly installed in the unit.
Check gas, and water - make sure there is gas in the bottle and the water supply is one - it might seem silly, but all these things count
Ensure expectations are realistic - some of the units we sell will only raise the temperature of the water a set amount - if it's the middle of winter - the water may not end up steaming how. These are cool little units, but they can only do so much.
First and foremost though - double-check those batteries!