h b Smmith Boiler

Tony1805

I have an h b Smith boiler model G100-W-6 HSID when the t-stat calls for heat everything works the pump turns on the zone valve opens the hot surface ignition control gets power the glow coil comes on the gas valve open and the burner ignights but it only stays on for about 15 seconds and it goes out I tried changing the flame sensor probee and the hot surface ignition control but no help whats my next step