Johnson & Starley is a British heating manufacturer based in Northampton, founded in 1947. Known for their warm air heating systems, heat pumps, and combi boilers, they are particularly common in social housing. Their Aquastar range of combi boilers is well regarded for reliability.
Johnson & Starley Boiler Fault Codes
All Johnson & Starley Fault Codes 36
| Code | Fault | Severity | Type | View guide |
|---|---|---|---|---|
| 1 | Ignition Failure (Numeric Display) On Johnson & Starley models with numeric displays, code 1 indicates flame lockout after several… | Medium | DIY Check | View Guide |
| 2 | Flame Failure Flame lost. | High | Engineer | View Guide |
| 3 | Overheat (Numeric Display) On Johnson & Starley models with numeric displays, code 3 indicates the high water temperature… | High | Engineer | View Guide |
| 37 | Low Water Pressure (Numeric Display) On Johnson & Starley numeric display models, code 37 indicates low system water pressure. | Low | DIY Check | View Guide |
| 4 | APS Fault Air pressure switch issue. | High | Engineer | View Guide |
| 5 | Overheat Overheat protection. | High | Engineer | View Guide |
| E01 | Ignition Lockout The most common Johnson & Starley fault. The boiler has failed to ignite after multiple… | Medium | DIY Check | View Guide |
| E02 | False Flame Lockout The boiler's ionisation circuit has detected a flame when the gas valve should be closed.… | High | Engineer | View Guide |
| E03 | Overheat Lockout The boiler has overheated and the safety thermostat has triggered a lockout. | High | Engineer | View Guide |
| E04 | Return NTC Fault Return sensor faulty. | Medium | Engineer | View Guide |
| E05 | Fan Fault The boiler fan is not operating correctly - not starting, running too slowly, or speed… | High | Engineer | View Guide |
| E06 | Fan Fault Fan not operating. | High | Engineer | View Guide |
| E07 | Gas Valve Fault Gas valve not responding. | High | Engineer | View Guide |
| E08 | Flame Circuit Failure There is a fault in the flame monitoring circuit on the Johnson & Starley boiler's… | High | Engineer | View Guide |
| E09 | Gas Valve Feedback Error The gas valve is not responding correctly to control commands, or there is a feedback… | High | Engineer | View Guide |
| E10 | Overheat Safety thermostat activated. | High | Engineer | View Guide |
| E11 | PCB Fault Internal PCB error. | High | Engineer | View Guide |
| E12 | EEPROM Lockout There is a memory fault on the PCB. The boiler's configuration data cannot be read… | High | Engineer | View Guide |
| E13 | Low Pressure System pressure too low. | Low | DIY Check | View Guide |
| E14 | Pump Fault Pump not running. | High | Engineer | View Guide |
| E15 | Condensate Blocked Condensate pipe blocked. | Medium | DIY Check | View Guide |
| E16 | DHW NTC Fault Hot water sensor faulty. | Medium | Engineer | View Guide |
| E17 | Diverter Valve Fault Valve stuck. | Medium | Engineer | View Guide |
| E18 | APS Fault Air pressure switch fault. | High | Engineer | View Guide |
| E19 | Flame Instability Flame signal fluctuating. | High | Engineer | View Guide |
| E20 | Flame Lost Flame lost during operation. | High | Engineer | View Guide |
| E21 | Rapid Temperature Rise Flow temp rising too fast. | High | Engineer | View Guide |
| E22 | Combustion Fault Air/gas mixture outside limits. | High | Engineer | View Guide |
| E23 | Pressure Sensor Fault Sensor faulty. | Medium | Engineer | View Guide |
| E24 | Frost Protection Frost protection active. | Medium | DIY Check | View Guide |
| E33 | Return Thermistor Fault The return temperature sensor has a fault - open circuit, short circuit, or wiring issue. | Medium | Engineer | View Guide |
| E35 | Flow Thermistor Fault The flow temperature sensor has a fault. | Medium | Engineer | View Guide |
| F37 | Low Water Pressure The system water pressure is too low for safe operation on Johnson & Starley boilers. | Low | DIY Check | View Guide |
| F40 | Water Pressure Too High The system water pressure is too high - above 3 bar. | Medium | Engineer | View Guide |
| F52 | DHW Sensor Fault The domestic hot water temperature sensor has a fault. | Medium | Engineer | View Guide |
| F53 | Flue Temperature Sensor Lockout The flue gas temperature sensor has triggered a lockout due to excessive flue temperatures or… | High | Engineer | View Guide |