Viessmann Boiler Fault Codes
If an issue occurs with your Viessmann boiler a display fault code on the control panel may show.
The fault codes will include letters or numbers or both. 
The fault codes are used to help you and your heating engineer identify and solve issues over the phone or in person.
Viessmann fault codes apply to all Viessmann boilers or some will only apply to certain models.
If a fault code has shown on your Viessmann boiler display, see the table below to identify the issue:
Viessmann Boiler Fault Code 5C, 5D, 5E and 5F
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300-K WITH VITOTRONIC 200 | CONTROL MODE – COMMUNICATION FAULT – VITOTRONIC 100 OF BOILER 5-8 |
Viessmann Boiler Fault Code 10
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200-W / 222-F / VITOTRONIC 300 / 200 / 200-H / 050/200-H / 300-K / VITOCONTROL-S | BOILER OPERATES BASED ON OUTDOOR TEMPERATURE OF 32°F / 0°C SHORT CIRCUIT – OUTDOOR TEMPERATURE SENSOR |
| VITOTRONIC 300-K, MW2S WITH VITOTRONIC 100 / VITODENS 100-W (COMBIPLUS) / 200-W / VITOCONTROL-S WITH VITOTRONIC 100 | CONTROLS AS IF THE OUTDOOR TEMPERATURE / CONSTANT MODE OUTDOOR TEMPERATURE SENSOR SHORTED OUT |
Viessmann Boiler Fault Code D4
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300 / VITOTRONIC 300-K WITH VITOTRONIC 300 | BOILER COOLS DOWN FAULT, SAFET EQUIPMENT AT X2 / X3 / X7 OF PLUG-IN ADAPTOR 2 FOR EXTERNAL SAFETY EQUIPMENT |
| VITODENS 200 | BOILER OPERATES IN EMERGENCY MODE (AFTER APPROX. 30MIN. BUS FAULT) OR BOILER COOLS DOWN INTERNAL BUS FAULT OR OPEN CIRCUIT – INTERNAL BUS CONNECTION |
Viessmann Boiler Fault Code 18 and D1
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 100 / 200-W / 222-F / VITOTRONIC 300-K WITH 100 / VITOCONTROL-S | OPERATES ON OUTDOOR TEMPERATURE OF 32°F / 0°C CONSTANT MODE OUTDOOR TEMPERATURE SENSOR CABLE BROKEN |
| VITOTRONIC / 100 / 200 / 300 / 050/200-H / 300-K / VITOCONTROL-S, MW1 WITH VITOTRONIC 100 | OPERATES ON BASIS OF 32°F / 0°C OUTDOOR TEMPERATURE OPEN CIRCUIT – OUTDOOR TEMPERATURE SENSOR |
| VITOTRONIC 200-H / VITOTRONIC 300-K, MW1B WITH VITOTRONIC 300 / VITOTRONIC 300-K, MW2B WITH VITOTRONIC 200 | CONTROLS AS IF THE OUTDOOR TEMPERATURE LEAD BREAK – OUTDOOR TEMPERATURE SENSOR |
| VITOTRONIC 050/200-H | ACTIVATES AFTER 0°C / 32°F OUTDOOR TEMPERATURE CABLE BREAK – OUTDOOR TEMPERATURE SENSOR |
| VITODENS 100-W | BURNER IN FAULT MODE DIP SWITCH S2 IS SET TO ‘ON’ |
Viessmann Boiler Fault Code A4
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 222-F | BURNER BLOCKED – THE VENTING PROGRAM STARTED AUTOMATICALLY AIR LOCK IN THE INTERNAL CIRCULATION PUMP OR MINIMUM FLOW RATE NOT ACHIEVED |
Viessmann Boiler Fault Code 0C
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 100-W | BURNER BLOCKED – INSUFFICIENT POWER SUPPLY |
| VITODENS 200 | BURNER CONTROL SWITCHES TO LOCKOUT – FLAME SIGNAL STILL PRESENT AFTER SWITCHING OFF |
Viessmann Boiler Fault Code C1
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200 | BURNER CONTROL UNIT SWITCHES TO LOCKOUT (DUE TO LARGE LINE VOLTAGE FLUCTUATIONS) DIFFERENTIAL AIR PRESSURE SENSOR / OPEN CIRCUIT |
Viessmann Boiler Fault Code B9, ED, F0, F-E5, F-EC, F-ED, F-EE, F-EF, F-FD and F-FF
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 100 / 300 / VITOTRONIC 300-K WITH VITOTRONIC 300 | BOILER COOLS DOWN FAULT: MAXIMUM PRESSURE LIMITER 1 2 |
Viessmann Boiler Fault Code 41
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300 | OPERATION WITHOUT ACCOUNTING FOR RETURN WATER TEMPERATURE SHORT CIRCUIT – RETURN WATER TEMPERATURE SENSOR OF MIXING VALVE CIRCUIT 2 |
Viessmann Boiler Fault Code 88, 89 and E6
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 300-K WITH VITOTRONIC 100 / 200 | CONTROL MODE COMMUNICATION FAULT: VITOTRONIC 100 OF BOILER 1-4 |
Viessmann Boiler Fault Code AD
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200 | SETTING VIA SERVICE LEVEL NOT POSSIBLE DATA POINTS ARE NOT STORED – INTERNAL FAULT VR20 |
Viessmann Boiler Fault Code 19
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300 | ACTIVATES AFTER 0°C / 32°F OUTDOOR TEMPERATURE COMMUNICATION FAULT: WIRELESS OUTDOOR TEMPERATURE SENSOR |
Viessmann Boiler Fault Code 21
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 200 / 300 | OPERATION WITHOUT INFLUENCE OF RETURN WATER TEMPERATURE SHORT CIRCUIT – RETURN WATER TEMPERATURE SENSOR |
Viessmann Boiler Fault Code 0b
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200 | BURNER CONTROL SWITCHES TO LOCKOUT – FAN DOES NOT IDLE AFTER AUTO RESET (INCORRECT FAN RPM) SEVERE WIND CONDITIONS IN THE VENT SYSTEM |
| VITODENS 100-W | BURNER BLOCKED INSUFFICIENT WATER FLOW – INCORRECT FLOW DIRECTION – DEFECTIVE FLOW SWITCH. (BLOCKAGE) |
Viessmann Boiler Fault Code 20
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 300 / 300-K / 200 / 100 | STAND-ALONE CONTROL UNIT WITHOUT SUPPLY TEMPERATURE SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) SHORT CIRCUIT – COMMON SUPPLY TEMPERATURE SENSOR |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 300-K WITH VITOTRONIC 200 | VITOCONTROL-S CONTROLS IN A STAND-ALONE MANNER WITHOUT SUPPLY TEMPERATURE SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) COMMON SUPPLY TEMPERATURE SENSOR SHORTED OUT |
| VITOCROSSAL 300 | REGULATES WITHOUT SUPPLY TEMPERATURE SENSOR (LOW-LOSS HEADER) SHORT CIRCUIT – SYSTEM FLOW TEMPERATURE SENSOR |
| VITODENS 200-W / 222-F | REGULATES WITHOUT SUPPLY TEMPERATURE SENSOR (LOW-LOSS HEADER) SHORT CIRCUIT – SUPPLY SYSTEM TEMPERATURE SENSOR |
| VITOTRONIC 020/200-H / 200 / 200-H / 300 | MIXING VALVE CLOSES OR CLOSED SHORT CIRCUIT – SUPPLY TEMPERATURE SENSOR / MIXING VALVE CIRCUIT M1 |
| VITORONIC 300-K WITH VITOTRONIC 100 | VITOTRONIC 300-K, MW1S CONTROLS IN A STAND-ALONE MANNER WITHOUT STRAP-ON SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) SHORT CIRCUIT – STRAP-ON TEMPERATURE SENSOR |
| VITODENS 200-W | REGULATES WITHOUT SUPPLY TEMPERATURE SENSOR (LOW LOSS HEADER) SYSTEM SUPPLY TEMPERATURE SENSOR SHORTED OUT |
Viessmann Boiler Fault Code 55, 56 and 57
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300-K WITH VITOTRONIC 200 | CONTROL MODE MAINTENANCE OR FAULT ON VITOTRONIC 100 OF BOILER 5-8 |
Viessmann Boiler Fault Code EE and EF
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 100-W / 200 / 0 / VITOTRONIC 300 | BURNER BLOCKED FAULTY AIR PRESSURE SWITCH – AIR DAMPER (FLAP) STUCK |
Viessmann Boiler Fault Code FE4
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCROSSAL 200 | BURNER SHUTS DOWN MULTIPLE DETECTION OF UNDERVOLTAGE |
Viessmann Boiler Fault Code F-B7, F-F4, F-F2, F-F7, F-F8 and F-F9
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCROSSAL 200 | CASE A: BURNER CONTROL UNIT IN A FAULT STATE; SYSTEM COOLS DOWN; BURNER CONTROL LOCKED OUT. CASE B: TYPE OF CODING CARD CASE A: CODING CARD NOT INSERTED IN THE BURNER CONTROL UNIT; FAULTY OR INCORRECT CODING CARD. CASE B: CODING CARD DOES NOT MATCH BURNER CONTROL UNIT |
Viessmann Boiler Fault Code 50, 51, 58 and 59
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200-W / 222-F | NO DHW HEATING / FAULT WITH DHW SHORT CIRCUIT/OPEN CIRCUIT – DHW TANK TEMPERATURE SENSOR OR LEAD BREAK |
Viessmann Boiler Fault Code A9, BA, BB, BC & FE0
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200 | BOILER COOLS DOWN SENSOR INPUTS ARE NOT READ CORRECTLY |
Viessmann Boiler Fault Code F-FA, F-FB and FR
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCROSSAL 200 / 400-620 / 186-311 | FAN RUNS WITHOUT DEMAND; BURNER CONTROL UNIT IN A FAULT STATE FAN NOT STOPPED; CABLE 100A FAULTY; FAN FAULTY; BURNER CONTROL UNIT FAULTY |
Viessmann Boiler Fault Code 8C, 8D, 8E and 8F
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300 | BURNER CONTROL UNIT IN A FAULT STATE LEAD BREAK, BOILER WATER TEMPERATURE SENSOR, BURNER CONTROL UNIT |
Viessmann Boiler Fault Code 52
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 300 | CONTROL MODE SHORT CIRCUIT – SUPPLY TEMPERATURE SENSOR LOW-LOSS HEADER |
| VITODENS 100-W COMBIPLUS | BURNER BLOCKED (COMBIPLUS ONLY) FLOW SENSOR SHORTED OUT |
Viessmann Boiler Fault Code 38
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200-W / 222-F / COMBIPLUS | BURNER BLOCKED BOILER WATER TEMPERATURE SENSOR CABLE BROKEN |
| VITOTRONIC 100 / 200 / 300 / VITOCONTROL-S WITH VITOTRONIC 100 | BURNER IS SWITCHED ON AND OFF BY ADJUSTABLE HIGH LIMIT OPEN CIRCUIT – BOILER TEMPERATURE SENSOR |
| VITOTRONIC 300-K WITH VITOTRONIC 300 | BURNER IS STARTED AND STOPPED VIA A TEMPERATURE CONTROLLER LEAD BREAK, BOILER WATER TEMPERATURE SENSOR |
| VITODENS 100-W | BURNER BLOCKED BOILER WATER TEMPERATURE SENSOR LEAD BROKEN |
Viessmann Boiler Fault Code A7
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 /VITOTRONIC 100 / VITOTRONIC 300-K WITH VITOTRONIC 300 | CONTROL MODE ISOLATION VALVE CONFIGURATION FAULT – OC:2, OC:3 OR OC:4 SET AND CODING 4E:1 NOT SET |
Viessmann Boiler Fault Code 0F
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 222-F | CONTROL MODE CODE 0F IS ONLY DISPLAYED IN THE FAULT HISTORY (SERVICE REQUIRED) |
| VITOTRONIC 300 / VITOTRONIC 300-K WITH VITOTRONIC 300 / VITODENS 200-W / VITOCONTROL-S WITH VITOTRONIC 100 | CONTROL MODE – CONTROLLED OPERATION CODE 0F IS ONLY DISPLAYED IN THE FAULT HISTORY (SERVICE REQUIRED) |
| VITOTRONIC 200 /300 | NORMAL OPERATION SERVICE REQUIRED |
| VITOCONTROL-S, MW1 WITH VITOTRONIC 100 / VITOTRONIC 300-K, MW1S WITH VITOTRONIC 100 | CONTROL MODE MAINTENANCE 0F IS ONLY DISPLAYED IN THE FAULT HISTORY |
Viessmann Boiler Fault Code E1, E7, E8, E9, EA, EB, EC and FF2
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200-W / 222-F /VITOTRONIC 300 | BURNER IN FAULT MODE HEATING WATER FLOW RATE TOO LOW DURING CALIBRATION; FLOW SWITCH CAUSED SHUTDOWN |
Viessmann Boiler Fault Code 29, 41, 49, F80, F81, F83, F88 and F89
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOTRONIC 200 / 300 | NORMAL OPERATION WITHOUT INFLUENCE OF RETURN WATER TEMPERATURE OPEN CIRCUIT 1 OR 2 – RETURN WATER TEMPERATURE SENSOR (OF MIXING VALVE CIRCUIT 1) |
Viessmann Boiler Fault Code A3, B0, F1, E-E1 and F-E2
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCROSSAL 300 / VITODENS 200-W / 222-F / 300 | CONTROL MODE (STAYS IN FACTORY DEFAULT SETTING) FAULTY PROGRAMMING UNIT |
Viessmann Boiler Fault Code 28
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 | VITOCONTROL-S, VD2/CT3/CM2 CONTROLS IN A STAND-ALONE MANNER W/O SUPPLY TEMPERATURE SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) OPEN CIRCUIT – COMMON SUPPLY TEMPERATURE SENSOR |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 300-K WITH VITOTRONIC 100 | VITOCONTROL-S, WB2B CONTROLS IN A STAND-ALONE MANNER W/O SUPPLY TEMPERATURE SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) COMMON SUPPLY TEMPERATURE SENSOR CABLE BROKEN |
| VITOCROSSAL 300 / VITODENS 200-W / 22-F | REGULATES WITHOUT SUPPLY TEMPERATURE SENSOR (LOW-LOSS HEADER) SYSTEM SUPPLY TEMPERATURE SENSOR CABLE BROKEN |
| VITOTRONIC 050/200-H | MIXING VALVE CLOSES CABLE BREAK – SUPPLY TEMPERATURE SENSOR |
| VITOTRONIC 050/200-H | MIXING VALVE IS CLOSED OPEN CIRCUIT – SUPPLY TEMPERATURE SENSOR OF MIXING VALVE CIRCUIT M1 |
| VITOTRONIC 200-H / VITOTRONIC 200 / 300 | MIXING VALVE IS BEING CLOSED LEAD BREAK, SUPPLY TEMPERATURE SENSOR, HEATING CIRCUIT WITH MIXING VALVE M1 (HEATING CIRCUIT 1) |
| VITOTRONIC 300 / 300-K WITH VITOTRONIC 300 / 200 | STAND-ALONE CONTROL UNIT WITHOUT SUPPLY TEMPERATURE SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) LEAD BREAK, COMMON SUPPLY TEMPERATURE SENSOR |
| VITOTRONIC 300-K WITH VITOTRONIC 100 | VITOTRONIC 300-K, MW1S CONTROLS IN A STAND-ALONE MANNER W/O STRAP-ON SENSOR (SUPPLY TEMPERATURE MIGHT NOT BE HIGH ENOUGH) OPEN CIRCUIT – STRAP-ON TEMPERATURE SENSOR |
Viessmann Boiler Fault Code B1
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOTRONIC 100 / 200 / 300 / VITOTRONIC 300-K WITH VITOTRONIC 100 | EMISSIONS TEST MODE INTERNAL ELECTRONICS FAULT |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITODENS 200-W | REGULATES AS IF THE OUTSIDE TEMPERATURE IS 32°F (0°C) INTERNAL FAULT |
| VITOTRONIC 020/200-H | UNDEFINED CONTROL CHARACTERISTICS INTERNAL ELECTRONICS FAULT |
Viessmann Boiler Fault Code E4
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITOCROSSAL 300 / VITODENS 200-W / 222-F / VITOTRONIC 300 | BURNER IN FAULT MODE AT BURNER START, FLAME SIGNAL IS TOO WEAK OR MISSING |
Viessmann Boiler Fault Code A0, A1, A2, AA and AC
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITODENS 200 | PUMP RUNS AT MAX SPEED OPEN CIRCUIT – BUS CONNECTION WITH VARIABLE SPEED HEATING CIRCUIT PUMP |
Viessmann Boiler Fault Code 30
| BOILER MODEL | SYSTEM BEHAVIOUR & DIAGNOSIS |
| VITOCONTROL-S WITH VITRTRONIC 100 / VITICROSSAL 300/ VITODENS 200-W / 222-F / VITOTRONIC 100 / 200 / 300 | BURNER IS STARTED AND STOPPED VIA AN ADJUSTABLE HIGH LIMIT SHORT CIRCUIT – BOILER WATER TEMPERATURE SENSOR |
| VITOCONTROL-S WITH VITOTRONIC 100 / VITODENS 100-W (COMBIPLUS) / 200-1 | BURNER BLOCKED BOILER WATER TEMPERATURE SENSOR SHORTED OUT |
Viessmann Boiler Fault Codes – All Viessmann Boilers
| FAULT CODE | SYSTEM BEHAVIOUR & DIAGNOSIS |
| B3 and E5 | CONSTANT MODE – INVALID HARDWARE RECOGNISED |
| FA and FB | CONTROL MODE – COMMUNICATION FAULT |
| A8 | CONTROL MODE – COMMUNICATION FAULT – PROGRAMMING UNIT |
| 90, 91, 92, 93, 94, 98, 99, 9A, 9B, 9C, 9E, 9F and AB | CONTROL MODE – SHORT CIRCUIT – TEMPERATURE SENSOR [5] / [6] / [7] / [10] |
| C9, CA and CB | BOILER DRIVES UP TO ELECTRONIC MAXIMUM LIMIT BOILER DOES NOT LOG IN AT THE CASCADE CONTROL UNIT |
| 5A, B7 and B8 | CONTROL MODE – LEAD BREAK, LOW-LOSS HEADER SUPPLY TEMPERATURE SENSOR BURNER BLOCKED / CONTROL MODE – SENSOR CABLE BROKEN |
| CC and F0 | BURNER IN FAULT MODE IONISATION CURRENT TOO HIGH DURING CALIBRATION – BOILER TEMPERATURE LIMITER RESPONDED (F2) – AIR OR BLOCKAGE IN SYSTEM/PUMP FAILURE |
| B6 | CONTROL MODE OPEN CIRCUIT – KM BUS TO SOLAR CONTROL UNIT – EXTENSION AM1 / DE1-DE3 M1 – COMMUNICATION FAULT |
| D5 | BURNER BLOCKED FLUE GAS TEMPERATURE SENSOR NOT PROPERLY POSITIONED / CHECK SENSOR EXTERNAL PUMP FITTED ON THE SYSTEM (100-W) A-3 FAULT |
| 60, 68, 70, 78, BD, BE and BF | NO OUTPUT REDUCTION – RETURN CONTROL OPEN – BOILER WITH MAXIMUM TEMPERATURE SHORT/OPEN CIRCUIT – TEMPERATURE SENSOR [17A] |
| E2 and E3 | BURNER BLOCKED – FAULT: SUPPLY VOLTAGE 24V |
| 40 and 44 | MIXING VALVE CLOSES HEATING CIRCUIT 2 WITH MIXING VALVE SUPPLY SHORT CIRCUIT ON TEMPERATURE SENSOR |
| 48 and 4C | MIXING VALVE CLOSES OR CLOSED HEATING CIRCUIT 2 WITH MIXING VALVE SUPPLY TEMPERATURE SENSOR CABLE BROKEN / OPEN CIRCUIT |
| FC | BURNER IN FAULT MODE GAS VALVE FAULTY OR FAULTY MODULATION VALVE CONTROL / OR VENT SYSTEM BLOCKED. CHECK THE FAN, FAN CABLE AND PCB |
| FE | BURNER BLOCKED OR IN FAULT MODE STRONG INTERFERENCE (EMC) FIELD NEARBY OR FAULTY MAIN PCB |
| B2 | CONTROL MODE – INTERNAL ELECTRONICS FAULT |
| B5 | CONTROL MODE – EXTERNAL SAFETY EQUIPMENT |
| 80, 81, 82, 83 and FD | BURNER CONTROL UNIT IN A FAULT STATE; SYSTEM COOLS DOWN; BURNER CONTROL UNIT LOCKED OUT SHORT CIRCUIT – BOILER WATER TEMPERATURE SENSOR, BURNER CONTROL UNIT |
| B4 | NORMAL OPERATION / FAULT AROUND BURNER CONTROL UNIT INTERNAL FAULT (PCB) |
| C2-C8, CD-CF, D2-D8, DA-DF and E0 | BOILER COOLS DOWN FIXED HIGH LIMIT HAS RESPONDED OR FUSE F2 HAS BLOWN |
| F5 | GAS PRESSURE SWITCH SHOWS NO GAS PRESSURE / ELECTRICAL CONNECTION FAULT GAS SHUT-OFF VALVE CLOSED; GAS PRESSURE SWITCH FAULTY; MULTIPLE GAS PROBLEMS WITH GAS SUPPLY |
| F6, 58, F9, F-E1, F-E2 and F-F6 | BURNER IN FAULT MODE / EMERGENCY OPERATION FAN NOT AT STANDSTILL / PLUG-IN CONNECTION |