No ignition. ?

Hi
My daughters heating has just died on her, although I am not a plumber or gas fitter I managed to go through the basics to see if it could be something simple, but unfortunately it wasn`t.
It is an old back boiler system of which she has had the front fire changed some time ago, the problem is that the back burners for the heating is not igniting, the pilot light is on and I can only assume that the pump is working because I can feel and hear it. I have no way of checking if the boiler thermo is functioning properly, I have also checked the header tanks in the loft area and they are both in working order, I have also cleaned the main burners and the rest of the rear of the fire, thank you for any advice.