Fondital Boilers Error Codes

A01

Boiler does not ignite, display shows A01, no flame symbol, heating and hot water unavailable

Ignition Failure / No Flame Detection

A02

Boiler locks out with A02, burner shuts down shortly after ignition, repeated failed starts

Flame Loss During Operation

A03

Boiler stops with A03, temperature rises quickly, radiators very hot, pump may be noisy

Overheating / Safety Thermostat Intervention

A04

Boiler shows A04, will not start, pressure gauge indicates low or zero pressure

Low Water Pressure / Insufficient System Charge

A05

Boiler displays A05, fan runs but burner does not ignite, sometimes accompanied by whistling or wind noise

Flue Gas Exhaust / Air Pressure Fault

A06

Boiler shows A06, ignition attempts are irregular, sometimes with loud clicking, no stable flame

Ignition Control / Spark Fault

A07

Boiler locks out with A07, fan may run continuously, no ignition sequence

Fan / Airflow Control Fault

A08

Boiler shows A08, no heating or hot water, pump may run briefly then stop

Flow Sensor / Circulation Fault

A09

Boiler displays A09, domestic hot water temperature unstable or excessively hot

DHW Temperature Sensor / Modulation Fault

A10

Boiler shows A10, heating temperature reading is incorrect or fluctuates rapidly

Flow/Return NTC Sensor Fault

A11

Boiler displays A11, burner stops, sometimes accompanied by gurgling noises in the boiler

Insufficient Water Circulation / Air in System

A12

Boiler shows A12, no domestic hot water even though heating works correctly

DHW Flow Detection Fault

A13

Boiler locks out with A13, often after long operation, casing may feel unusually warm

Flue Gas Overtemperature / Safety Cut-out

A14

Boiler shows A14, burner stops, may occur during DHW draw-off, water temperature drops suddenly

Gas Valve Modulation / Overpressure Fault

A15

Boiler displays A15, no response to thermostat demand, heating symbol may flash

Room Thermostat / External Control Fault

A16

Boiler shows A16, heating temperature limited, boiler may cycle frequently

Return Temperature Sensor / Anti-condensation Control Fault

A17

Boiler displays A17, pump runs but burner does not start, especially in heating mode

Flow Switch / Differential Pressure Fault

A18

Boiler shows A18, condensate may be visible around the base, unit may be noisy

Condensate Drain / Siphon Fault

A19

Boiler displays A19, burner stops, may coincide with gas meter change or supply interruption

Gas Supply Interruption / Lockout

A20

Boiler shows A20, display may indicate communication error with remote control or zone module

Communication Fault (Bus Error)

Symptom

Boiler display is blank or intermittently turns off, but mains power is present

Power Supply / Control Panel Fault

Symptom

Boiler does not produce hot water when more than one tap is opened

Insufficient DHW Capacity / Flow Limitation

Symptom

Boiler does not respond to heating demand, but hot water works normally

Heating Demand / Diverter Valve Fault

Symptom

Boiler emits a burning smell or plastic odour during operation

Overheating Electrical Component or Dust Burn-off

Symptom

Boiler fan runs continuously even when there is no heating or hot water demand

Fan Overrun / Stuck Relay

Symptom

Boiler flue terminal shows white staining and there is excessive condensate dripping outside

Condensate Management / Flue Installation Issue

Symptom

Boiler frequently goes into anti-cycling or anti-freeze mode even when not required

Control Logic / Sensor Placement Issue

Symptom

Boiler frequently loses pressure and needs topping up every few days

Chronic Pressure Loss

Symptom

Boiler ignites with a loud bang or pop (delayed ignition)

Delayed Ignition / Gas-Air Mixture Fault

Symptom

Boiler leaking water from underneath the casing or from safety valve discharge pipe

Internal Water Leak / Overpressure Discharge

Symptom

Boiler makes loud banging or knocking noises when starting or stopping heating

Kettling / Thermal Shock in Heat Exchanger

Symptom

Boiler runs but gas consumption seems unusually high compared to previous seasons

Reduced Efficiency / Combustion or Scaling Issue

Symptom

Boiler runs for only a short time then stops, radiators never reach set temperature

Short Cycling / Oversized Boiler or Sensor Misreading

Symptom

Boiler vibrates excessively or resonates through the flue and pipework during operation

Mechanical Vibration / Fan or Pump Imbalance

Symptom

Domestic hot water temperature fluctuates between hot and cold during shower use

Inconsistent DHW Temperature Control

Symptom

Radiators only partially heat up or some remain cold while boiler runs

Poor Circulation / System Balancing Issue