code: public function setEcoTemperatures($temp_low, $temp_high, $serial_number = NULL) {
          $serial_number = $this->getDefaultSerial($serial_number);
          $temp_low = $this->temperatureInCelsius($temp_low, $serial_number);
          $temp_high = $this->temperatureInCelsius($temp_high, $serial_number);
          $data = array();
          if ($temp_low === FALSE) {
              $data['away_temperature_low_enabled'] = FALSE;
          } elseif ($temp_low != NULL) {
              $data['away_temperature_low_enabled'] = TRUE;
              $data['away_temperature_low'] = $temp_low;
          }
          if ($temp_high === FALSE) {
              $data['away_temperature_high_enabled'] = FALSE;
          } elseif ($temp_high != NULL) {
              $data['away_temperature_high_enabled'] = TRUE;
              $data['away_temperature_high'] = $temp_high;
          }
          $data = json_encode($data);
          return $this->doPOST("/v2/put/device." . $serial_number, $data);
      }
docs: Change the thermostat ECO temperatures.
  
  @param float|bool $temp_low      ECO low temperature. Use FALSE to turn it Off (only the safety minimum temperature will apply).
  @param float|bool $temp_high     ECO high temperature. Use FALSE to turn it Off (only the safety maximum temperature will apply).
  @param string     $serial_number The thermostat serial number. Defaults to the first device of the account.
  
  @return stdClass|bool The object returned by the API call, or FALSE on error.