The symptoms you described—continuous running without reaching the set temperature and triggering the "Er" error—indicate a likely fault in the temperature sensor or thermostat integrated into the electronic control board of your Covenant 48" Electric RV Fireplace (model WD914-48FT). To proceed with a replacement of the electronic control board (LFP-NEWTSPCBOARD), it is essential to first have the unit evaluated by Lippert's technical support team, as they are and best equipped to diagnose and authorize warranty repairs. Please contact Lippert Customer Service / Technical Support at [phone removed] and have your model and serial numbers ready. Once Lippert confirms the issue and provides authorization, you can order the replacement electronic control board from Elkhart RV Parts. We also recommend following the troubleshooting guide and manual provided with your unit to verify the issue. Returning the faulty board for confirmation is welcomed after evaluation. This process ensures a proper and warranty-compliant repair of your electric RV fireplace.