most modern boilers are cold cased an as such can be mounted on a combustible surface you could check that with manufacturers instructions but it has to be secure which your doesnt look to be
the easist way out of the situation you find your self in would be to remove the window and all frames and have the window bricked up then the boiler could be rehung onto the brick work subject to clearances being correct
i would also get some clips on the pipework
the easist way out of the situation you find your self in would be to remove the window and all frames and have the window bricked up then the boiler could be rehung onto the brick work subject to clearances being correct
i would also get some clips on the pipework