relating to potterton suprima 30 boiler?

The boiler runs fine but after about 3 to 5 mins unfortunately then stops (power and lights still on). It can be re started by turning off the power supply and on to re start, One this is carried out it then goes through th setup routine perfectly and runs again for 3-5 mins then stops. When it stops the red light comes on and green light starts flashing. Any help would be apprecaited to locate the problem (eg PCB, flow meter, air pressure switch etc etc). I think its probably something simple but am not sure.