EMB ERJ 145 ER/LR
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Workload; Fatigue
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Notified ATC and diversion due to burning smell inside flight deck. Passing through FL310 Captain asked First Officer (FO) if he smelled anything out of the ordinary.  FO stated he smelled something like burning toast.  Captain rang flight attendant and asked the same to which she stated burnt toast as well.  Captain notified ATC and we diverted to ZZZ.  During descent smell went away but reoccurred intermittently.  Performed overweight landing smoothly and stopped on runway.  Confirmed smell was gone with flight attendant and taxied to gate while fire rescue followed.  Passengers deplaned.  Maintenance met us at gate and we were able to duplicate smell when packs were turned on using APU. First Officer flew aircraft while Captain performed checklist.  We landed without further incident.  Captain and FO spoke and initially felt okay to continue on [from] ZZZ.  However as time passed and adrenaline wore off fatigue set in.  We spoke again and both determined that we could not safely operate the flight [from] ZZZ.
When climbing through 31;000 feet; both the FO and I noticed a distinct odor that smelled like burning toast. We immediately asked the FA if she smelled it as well and she did. I then [requested priority handling] with ATC and the FO initiated a descent as we diverted to ZZZ1. Once we descended through 31;000 feet; the smell dissipated. Throughout the flight; we smelled the burning order intermittently for short durations of only a few seconds. Once we landed; we came to a stop on the runway and assessed the situation. The odor was gone so we taxied back to our gate under our own power with fire trucks in tow. When at the gate with the door open and APU bleed and packs on; the odor came back and intensified. Maintenance was able to reproduce this on the ground.
EMB-145 flight crew reported a fume event that resulted in a diversion. After landing when the APU bleed and packs were on; the odor returned.