Ruud Achiever 90 Plus wont start

Question

I have a Ruud Achiever 90 Plus that wont start. I have checked the inlet/outlets outside the house and neither of them are blocked. When I turn the power on to the unit the Power light turns on and the Ok light blinks four times, stops, then blinks four times again it repeats this over and over but doesn't start. I have looked on the panel and there is no Light flashing diagnostics or codes. So if you could tell me what the light flashing four times means it would be appreciated. Thanks.