have baxi doing the same starts but then in 5secs flame goes out ?

Have tested flow switches they work ! have tested main pcb two relays switch on but one never moves tested gas valve coil, it has a resistance on coil 60 flow ratedhw to down stairs tap Half a pint in 4secs hot water upstairs 1pint in 4secs green neon not on but has power to it can any one help please pretty please?