diff --git a/README.md b/README.md
index dd3c606..a6839c7 100644
--- a/README.md
+++ b/README.md
@@ -145,6 +145,7 @@ printer.write_first_ti_received_time(2000, 1, 2)
 
 ```
 TimeoutError
+ValueError
 ```
 
 (And *pysnmp* exceptions.)
diff --git a/epson_print_conf.py b/epson_print_conf.py
index 26a996e..3c6bc34 100644
--- a/epson_print_conf.py
+++ b/epson_print_conf.py
@@ -381,7 +381,7 @@ class EpsonPrinter:
             if ret:
                 stat_set[method[4:]] = ret
             else:
-                logging.error(f"No value for method '{method}'.")
+                logging.info(f"No value for method '{method}'.")
         return stat_set
 
     def caesar(self, key):
@@ -402,8 +402,12 @@ class EpsonPrinter:
             msb = oid // 256
             oid = oid % 256
         if msb > 255:
+            logging.error("EpsonPrinter - invalid API usage")
             return None
-        if not self.parm or 'read_key' not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if 'read_key' not in self.parm:
             return None
         return (
             f"{self.eeprom_link}"
@@ -430,9 +434,13 @@ class EpsonPrinter:
             msb = oid // 256
             oid = oid % 256
         if msb > 255:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
             return None
         if (
-            not self.parm or 'write_key' not in self.parm
+            'write_key' not in self.parm
                 or 'read_key' not in self.parm):
             return None
         write_op = (
@@ -446,7 +454,7 @@ class EpsonPrinter:
             f".{self.caesar(self.parm['write_key'])}"
         )
         if self.dry_run:
-            logging.debug("WRITE_DRY_RUN: %s", write_op)
+            logging.warning("WRITE_DRY_RUN: %s", write_op)
             return self.eeprom_oid_read_address(oid, label=label)
         else:
             return write_op
@@ -471,12 +479,12 @@ class EpsonPrinter:
         for response in iterator:
             errorIndication, errorStatus, errorIndex, varBinds = response
             if errorIndication:
-                logging.error("snmp_mib error: %s", errorIndication)
+                logging.info("snmp_mib error: %s", errorIndication)
                 if " timed out" in errorIndication:
                     raise TimeoutError(errorIndication)
                 return False
             elif errorStatus:
-                logging.error(
+                logging.info(
                     'snmp_mib PDU error: %s at %s',
                     errorStatus.prettyPrint(),
                     errorIndex and varBinds[int(errorIndex) - 1][0] or '?'
@@ -488,9 +496,9 @@ class EpsonPrinter:
                         return varBind[1].asOctets()
                     else:
                         return varBind[1].prettyPrint()
-            logging.error("snmp_mib value error: invalid multiple data")
+            logging.info("snmp_mib value error: invalid multiple data")
             return False
-        logging.error("snmp_mib value error: invalid data")
+        logging.info("snmp_mib value error: invalid data")
         return False
 
     def read_eeprom(
@@ -512,7 +520,7 @@ class EpsonPrinter:
         try:
             response = re.findall(r"EE:[0-9A-F]{6}", response.decode())[0][3:]
         except (TypeError, IndexError):
-            logging.error(f"Invalid read key.")
+            logging.info(f"Invalid read key.")
             return None
         chk_addr = response[0:4]
         value = response[4:6]
@@ -538,7 +546,10 @@ class EpsonPrinter:
             value: int,
             label: str = "unknown method") -> None:
         """Write a single byte 'value' to the Epson EEPROM address 'oid'."""
-        if not self.parm or "write_key" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return False
+        if "write_key" not in self.parm:
             logging.error(
                 f"Missing 'write_key' parameter in configuration.")
             return False
@@ -555,7 +566,7 @@ class EpsonPrinter:
         if response:
             logging.debug(f"  RESPONSE: {repr(response)}")
         if not self.dry_run and response and not ":OK;" in repr(response):
-            logging.error("Write error")
+            logging.info("Write error")
             return False  # ":NA;" is an error
         return True
 
@@ -623,25 +634,32 @@ class EpsonPrinter:
         }
 
         if len(data) < 16:
+            logging.info("status_parser: invalid packet")
             return "invalid packet"
         if data[:11] != b'\x00@BDC ST2\r\n':
             logging.debug("Unaligned BDC ST2 header. Trying to fix...")
             start = data.find(b'BDC ST2\r\n')
             if start < 0:
+                logging.info(
+                    "status_parser: "
+                    "printer status error (must start with BDC ST2...)")
                 return "printer status error (must start with BDC ST2...)"
             data = bytes(2) + data[start:]
         len_p = int.from_bytes(data[11:13], byteorder='little')
         if len(data) - 13 != len_p:
+            logging.info("status_parser: message error (invalid length)")
             return "message error (invalid length)"
         buf = data[13:]
         data_set = {}
         while len(buf):
             if len(buf) < 3:
+                logging.info("status_parser: invalid element")
                 return "invalid element"
             (ftype, length) = buf[:2]
             buf = buf[2:]
             item = buf[:length]
             if len(item) != length:
+                logging.info("status_parser: invalid element length")
                 return "invalid element length"
             buf = buf[length:]
             logging.debug(
@@ -797,6 +815,8 @@ class EpsonPrinter:
             elif ftype == 0x36:  # Paper count information
                 if length != 20:
                     data_set["paper_count"] = "error"
+                    logging.info(
+                        "status_parser: paper_count error. Length: %s", length)
                     continue
                 data_set["paper_count_normal"] = int.from_bytes(
                     item[0:4] , "little", signed=True)
@@ -881,13 +901,16 @@ class EpsonPrinter:
             elif isinstance(result, str):
                 sys_info[name] = result
             else:
-                logging.error(
+                logging.info(
                     f"No value for SNMP OID '{name}'. MIB: {oid}.")
         return sys_info
 
     def get_serial_number(self) -> str:
         """Return serial number of printer."""
-        if not self.parm or "serial_number" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "serial_number" not in self.parm:
             return None
         return "".join(
             chr(int(value or "0", 16))
@@ -897,7 +920,10 @@ class EpsonPrinter:
 
     def get_stats(self, stat_name: str = None) -> str:
         """Return printer statistics."""
-        if not self.parm or "stats" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "stats" not in self.parm:
             return None
         if stat_name and stat_name in self.parm["stats"].keys():
             stat_info = {stat_name: self.parm["stats"][stat_name]}
@@ -923,7 +949,10 @@ class EpsonPrinter:
 
     def get_printer_head_id(self) -> str:  # to be revised
         """Return printer head id."""
-        if not self.parm or "printer_head_id_h" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "printer_head_id_h" not in self.parm:
             return None
         if "printer_head_id_f" not in self.parm:
             return None
@@ -967,7 +996,10 @@ class EpsonPrinter:
 
     def get_ink_replacement_counters(self) -> str:
         """Return list of ink replacement counters."""
-        if not self.parm or "ink_replacement_counters" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "ink_replacement_counters" not in self.parm:
             return None
         irc = {
             (
@@ -1002,7 +1034,10 @@ class EpsonPrinter:
 
     def get_waste_ink_levels(self):
         """Return waste ink levels as a percentage."""
-        if not self.parm or "main_waste" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "main_waste" not in self.parm:
             return None
         results = {}
         for waste_type in ["main_waste", "borderless_waste", "first_waste",
@@ -1020,7 +1055,10 @@ class EpsonPrinter:
 
     def get_last_printer_fatal_errors(self) -> str:
         """Return list of last printer fatal errors in hex format."""
-        if not self.parm or "last_printer_fatal_errors" not in self.parm:
+        if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
+            return None
+        if "last_printer_fatal_errors" not in self.parm:
             return None
         return self.read_eeprom_many(
             self.parm["last_printer_fatal_errors"],
@@ -1058,7 +1096,7 @@ class EpsonPrinter:
                     for j in response
             ]
         except Exception as e:
-            logging.debug(f"  CARTRIDGE MAP ERROR: {e}")
+            logging.info("  CARTRIDGE MAP ERROR: %s", e)
             return None
         try:
             return [
@@ -1074,7 +1112,7 @@ class EpsonPrinter:
                 } for i in cartridges
             ]
         except Exception as e:
-            logging.error(f"  CARTRIDGE VALUE ERROR: {e}")
+            logging.info("  CARTRIDGE VALUE ERROR: %s", e)
             return None
 
     def dump_eeprom(self, start: int = 0, end: int = 0xFF):
@@ -1091,6 +1129,7 @@ class EpsonPrinter:
         Set waste ink levels to 0.
         """
         if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
             return None
         if "raw_waste_reset" in self.parm:
             for oid, value in self.parm["raw_waste_reset"].items():
@@ -1113,11 +1152,13 @@ class EpsonPrinter:
             self, year: int, month: int, day: int) -> bool:
         """Update first TI received time"""
         if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
             return None
         try:
             msb = self.parm["stats"]["First TI received time"][0]
             lsb = self.parm["stats"]["First TI received time"][1]
         except KeyError:
+            logging.info("write_first_ti_received_time: missing parameter")
             return False
         n = (year - 2000) * 16 * 32 + 32 * month + day
         logging.debug(
@@ -1149,10 +1190,11 @@ class EpsonPrinter:
     def brute_force_read_key(self, minimum: int = 0x00, maximum: int = 0xFF):
         """Brute force read_key for printer."""
         if not self.parm:
+            logging.error("EpsonPrinter - invalid API usage")
             return None
         for x, y in itertools.permutations(range(minimum, maximum + 1), r=2):
             self.parm['read_key'] = [x, y]
-            logging.error(f"Trying {self.parm['read_key']}...")
+            logging.warning(f"Trying {self.parm['read_key']}...")
             val = self.read_eeprom(0x00, label="brute_force_read_key")
             if val is None:
                 continue
@@ -1285,7 +1327,7 @@ if __name__ == "__main__":
     )
     args = parser.parse_args()
 
-    logging_level = logging.INFO
+    logging_level = logging.WARNING
     logging_fmt = "%(message)s"
     env_key=os.path.basename(Path(__file__).stem).upper() + '_LOG_CFG'
     path = Path(__file__).stem + '-log.yaml'