whats the normal boiler cycling time with just underfloor heating running. Mine is burning for 2 and a half minutes and off for between six and ten minutes with just ufh i haven't check with rads upstairs on as well.
Since no one has answered 'till now: Either your boiler is oversized or your pump is not pumping enough. Two minutes running is certainly not economic. Every start uses a lot of energy and sets a lot of sooth on the (cold) heat exchanger. Try it out with all heat demanding apliances ON (UFH, radiators,storage tank) and see if it helps. If yes then you have an oversized boiler-at least oversized for the output demand where you experience the 2.5 minutes run. A modulating boiler would be the answer, check the Sedbuk homepage for choice: http://www.sedbuk.com/