[abisel]

There is a troubleshooting guide in the download area, right side of this web site:
https://www.modinehvac.com/web/products/residential-gashydronic-garage-heaters-hot-dawg/hot-dawg-power-vented-hd.htm

Also, if your unit is the HDB, the installation manual says to mount the unit 6 inches from combustible material. Your picture doesn't show 6" at the top. Just saying.