This is what the manual says, I have not had id happen but a couple friends of mine have. Hope it helps.
“ErH” Error Message
The grill has overheated, possibly due to grease fire or excess fuel.
Turn the grill OFF and allow to cool. Clean grill interior, remove excess pellets, and confirm positioning of all component parts. To CLEAR the error - Turn Temperature Dial to OFF. OPEN the lid, wait 3 or 4 minutes, then select desired temperature