riello motor no longer works (and yet it did before I took the pump apart?)?

Our boiler stopped working, I ruled out everything except the pump or something on the pump like the valve or solenoid. Anyway the burner works, the motor would come on, but it would lock out after the 12 second purge.

I thought maybe the pump was buggered, so I took the first lid off it and cleaned the filter in their, when that didn't work I took it off again only this time I undid the three screws under the filter and had a look inside the pump. Well, All I found was a few cogs and nothing was broken, the lug in the middle was spinning okay, so I put it all back together. Then when I turned the burner on to see if it would light, now even the motor won't run.

In the troubleshooting flow diagram int he manual for the boiler it suggests if the motor doesn't run the pump might be tight or seized... How could the pump seize up just because I took that lid off? I took it apart again, put it back together. Again, but it is still not working.

Now what do I do? Even if it was the solenoid that was wrong with it in the first place I can't test it now because nothing works. Most confusing.