View and Download Heatmiser PRT- B user manual online. Hi Peter I’ ve moved house , no longer have a Heatmiser but from memory I think there is a small battery somewhere on the circuit board. Sounds like this has failed and needs replacing. Also for: Prt- nts Prt- ets Prt- ents. Programmable Room Thermostat. Heatmiser prt ets manual. PRT- B Thermostat pdf manual download.