Not much at all to be honest as I'm on forums most of the time posting drivel £20 a week should more than cover it so just add on a quid to every regular job and you should be quids in.I hadly ever need to turn up the gas past the 1/4 mark just set on summer setting it's that efficent.
About 40c with the flow set to about 50 ish on the controller.For all these types of gas heaters to fire up you must have the flow dial set to minimum. Oh and the most important thing is to protect it from frost especially overnight. Either drain the heater down or have the back of the van heated somehow or the frost wil bugger it up.
Trippy, turn your water flow right down on your water pump, to about 25, and turn the flame dial right up, make sure the first windows you do tomorrow morning are on unheated conservatories.
How much you spend on gas per week mate?CheersTrippy