Vaillant Eco tec fault codes System boilers


Fault, Meaning, Official Cause, Our Comments 


F.00 Flow–NTC open circuit NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics 


F.01 Return–NTC open circuit NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics


 F.02 Domestic hot water outlet NTC open circuit (combination boiler only) NTC-connector not plugged in or loose, NTC defective connector on the electronics not plugged in correctly, cable defective 


F.10 Flow NTC short circuit NTC defective,cable/casing shortcut 

Check for leaks and water causing short circuit


F.11 Return NTC short circuit NTC defective, cable/casing shortcut 

Check for leaks and water causing short circuit


F.13 Tank NTC short circuit NTC defective,short circuit in cable harness, cable/casing shortcut

Check for leaks and water causing short circuit


F.20 Safety temperature limiter by NTC activated Flow-NTC not correctly thermal-connected or defective; appliance does not shut down 


F.22 Dry fire Too little water in the appliance, water pressure sensor defective, cable to pump or water sensor defective, pump blocked or defective, pump output too low 

Too much air in system or low water pressure


F.23 Water shortage, temperature difference between flow and return NTC too large Pump blocked or defective, pump output too low, flow and return NTC interchanged

Pump failure, flow and return reversed, air lock, blocked pipe, air in heat exchanger, or top up system in sealed system.  


F.24 Water shortage, temperature rise too quick Pump blocked, insufficient pump output, air in appliance, water pressure too low 


F.27 Incorrect sensing of flame Flame detector defective 


F.28 Appliance does not start: Attempts to ignite during start failed Faults in the gas supply such as: - Gas meter or gas pressure detector defective - Air in gas - Gas flow pressure too low - Fire protection tap has disengaged Faults in the gas valve, wrong gas setting, igniter (ignition transformer, ignition cable, ignition plug) defective, ionisation current stopped (cable, electrode), faulty earthing in appliance, electronics defective 

Check gas supply, check maintenance works by National Grid these can come as a surprise


F.29 Flame goes off during operation and subsequent ignition attempts failed Gas supply temporarily stopped, faulty earthing of appliance

Check gas supply, check maintenance works by National Grid these can come as a surprise 


F.32 Fan speed variation Fan blocked, plug not inserted correctly on fan, hall sensor defective, fault in cable harness, electronics defective 


F.49 eBUS undervoltage Short circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity 


F.61 Gas–valve control defective Short circuit/earth (ground) leak in cable harness to gas valves, gas valve assembly defective (earth/ground leak from coils), electronic control system defective 


F.62 Gas valve shut-off delay Gas valve leaking, electronics defective 

Check gas supply/valve


F.63 EEPROM error Electronics defective 


F.64 Electronics/NTC fault Short-circuit in flow or return NTC or electronics defective

also check for leaks and water causing short circuit 


F.65 Electronics temperature too high Electronics too hot due to external effect, electronics defective 


F.70 No valid DSN in display and/or mainboard Spare part failure display and mainboard interchanged at same time and device specific number not adjusted 


F.71 Flow NTC reports constant value (stuck at) Flow NTC is defective 


F.72 Flow and/or return NTC fault Flow and/or return NTC is defective (tolerances too big) 

(two different stats to check, also check pump and circulation)


F.73 Water pressure sensor signal out of range (too low) Cable to water pressure sensor is broken or has a short-circuit at 0 V or water pressure sensor defective

or sensor blocked


F.74 Water pressure sensor signal out of range (too high) Cable to water pressure sensor has a short-circuit at 5 V / 24 V or internal fault in water pressure sensor 


F.75 No pressure rise was detected on turning on the pump Water pressure sensor or/and pump defective Too little water in appliance; check adjustable by-pass; connect external expension vessel to return 

see f75 page (coming soon) Google f75 kit


F.76 Overheating protection on primary heat exchanger triggered Cable or cable connection of fuse in the primary heat exchanger defective, or primary heat exchanger defective 

Replacement stat is not necessarily available due to safety concerns following an F76 incident


F.77 condensate pump or feedback of accessories blocks heating condensate pump defective or flume flap feedback triggered 


F.78 wrong configuration with accessory link box VR65 connected to combination boiler con no communication to mainboard connection error display mainboard

Plug ins are not correct


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Gas Safe Reg no 305929    Company No. 07980305    VAT No. GB172932986    D-U-N-S Number: 21-827-8135

Primary Coverage;   

NW2 Willesden Green, Cricklewood, and Childs Hill   

NW3 Hampstead, Belsize   

NW5 Kentish Town, Camden   

NW6 West Hampstead, Kilburn, and Queens Park   

NW8 St Johns Wood   

NW10 Kensal Rise, Harlesden, Willesden   

NW11 Golders Green Hampstead Garden Suburb   

W9 Maida Vale   

W10 North Kensington, Queens Park   


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