Hi Eamonn, I don't think it could cause low ht voltage, but one thing that comes to mind is that these systems are very fussy about battery voltage, We had one that we tried getting running for about an hour or so, (it just happened to fail to start outside the shop across the road so it was pushed in) it was cranking over like a good un, but it would not spark, (or very weak)after about an hour of checking and cranking we checked the voltage at the battery and it was under 8v, so we put the jump leads on it and it started, so we removed the leads and it just cranked and cranked. So I wonder if you had 2 problems, jumped belt and low voltage due to everybody trying to start it. ?? New battery cured ours.