Hi, I know this is an old thread but google has it 1st place in it's results for this problem so for others I thought I would post how I fixed this issue.
As tamz says above the problem was caused by the boilers flow temp sensor detecting that the water was sufficiently hot with the effect that the boiler cycled on and off every minute.
As there was no way to adjust the boiler temp down I thought about this for a while and deduced that the water just wasn't getting pushed away from the boiler quick enough.
Mine is a micro bore system with an open vent condensing boiler pretty typical of houses built in the last 15 years or so.
Turning the system pump up to maximum did get the water moving away fast enough to fix the issue but I don't like things running at max and it soon caused a leak in the boiler manifold.
I was able to cure the problem by relieving the resistance in the rad system by opening up all the radiator's stop valves by a quarter turn. By adjusting them all by the same amount the rads stayed in balance and warmed up evenly and allowed the water to flow faster through the system and the boiler stopped tripping frequently.
