I would think the pump ..no circulation ..over heats .. cuts out ..
cools re-lights .. and so on .. pump change is quite easey .. just make
sure to bleed all the air out after or it wont run ... or you could
try bleeding it first .. may be just air locked ? i think you should
get water out of the pump when you remove the screw bung on the read of
the pump . may be just silted up


G .