Vokera Mynute 12-48 burner not firing?

Working on a Vokera Mynute 12-48 that won't light when there is demand for heat. Have replaced thermostat but still nothing. Have gone thru sequence of start up. There's 240 volts at flow switch and fan resistor (240v left side 180v on the right) but seems there's no voltage at terminal 3 or 1 on air pressure switch. Is this because the pump isn't turning over the flow switch to provide 240v to the air pressure switch and in turn not energising the gas valve? or could there be a deeper problem connected to pcb, solenoid or something?