Central heating not working?

My glow worm micron 50FF works for a short time then shuts down and both lights go out. Neither of the two lights are on or flashing so fault codes in manual do not help. Once it is cold boiler can be reset and starts up again for a short time before shutting down again. Fan, pump and mid point valve are all working, pcb has been replaced and problem is the same for both heating and hot water. Any suggestions please?