Pump runs when boiler satisfied?

I recently moved my central heating pump so as to give me heating for my towel rail off the primary circuit. All OK except that, when no heating on, just hot water, boiler keeps firing up for a few seconds every 6 or 7 minutes. When it stops, pump continues to run. I know it's supposed to run for a while but it 's on all the time. (not when hot water is turned off from programmer)Towel rail is off via lockshield valve. The Megaflow cylinder only used to call for heat every 5 or 6 hours before I moved pump. Also, programmable roomstat not connected but I guess that's irrelevant?
Any ideas guys?