C172 pilot discovers after being cleared for the ILS that his glide slope has failed. This information is not conveyed to ATC. The approach is continued using LOC minimums and a low altitude alert is generated before the reporter descends below the overcast and lands.

Narrative

In flight I discovered that my glide slope was not working. I failed to communicate this to ATC. I was not aware of this failure before the flight. Boston Approach asked me if I had intercepted the localizer which I had. I followed the localizer and got distracted because my glide slope never came in. The localizer went almost to full scale deflection before I noticed that it was deflected. Boston Approach never questioned my vertical or lateral navigation except to ask me if I had intercepted the localizer. When I passed over the LOM; I descended as I would on a localizer approach (without vertical guidance). After being handed over to LWM Tower; I was informed of a low altitude warning. I reported that I had broken out of the clouds and had the runway in sight. From my perspective; I broke out of the clouds at an altitude to make a normal glide path to the runway. To prevent this from reoccurring; ATC should question the pilot in flight of the error in navigation. Boston must have noticed some error and did not notify me until I was on the ground with LWM Ground. I was in error for not reporting an equipment malfunction.