i was called out to a ignition fault on a alpha boiler, it was going to lockout after lighting for about 5min. i cleaned out the venturi, and fitted new temperature sensors, i had also fitted a new diverter valve previously for another fault on the boiler. whats happening now is the boiler will light but stay on high gas and not modulate, it reaches the temp and goes off it doesn't go to lockout but isn't running properly i suspect its the gas valve but have spent enough money on parts for this boiler and don't want to cost the customer any more unnecessary spending if possible. could anyone give me any advice if they have come across this problem before?