Assuming this unit has been working OK till now, probably either the extraction fan did not kick on, or the damper did not open - or possibly it is real windy and natural drafting is messing with the sensors.
Heating and A/C is your Search the List category to find a well-rated and reviewed vendor to call if you do not already have a go-to HVAC guy.
Check your manual or find it online - the number and color and sequence or timing of blinking lights is usually a code for a specific issue, as opposed to a numeric code on more sophisticated electronic systems.
