look in ur instructions what does 03 stand 4, it should not matter weather ur boiler is set 2 max it should work if it shows a fault code, then u have a fault, just gues if it doesnt work on max then maybe, u have a overheat problem, circulation problem (pump, diverter, sludge) could be low gas pressure inlet or max settings out if ur boiler can not be run on its maximum settings 2 carry out mandatory 26.9 gas checks, burner pressure, gas rate, fga then u have got an AT RISK APPLIANCE
Blaiross, December 2011