E10 fault is - No flow during vent cycle
Which model of avanta is it - combi, system or heat only?
Usually due to faulty pump, low water pressure, air locked (try bleeding radiators), if it is the heat only version the pump needs to be wired and conrolled by the boiler or will throw up E10 faults.
If it is the combination boiler the diverter valve sticking can cause it, also check that all the radiator valves are open & any thermostatic valves are not seized.
Failing that how old is the boiler, 5 years warranty on these (sometimes only 2 years on parts, depending on who fitted it), warranty call to heat team.
Will be worth a call to the original installer, we always attend to boilers we have fitted even if still within the warranty period.