Baxi
Baxi 600 System 2 18kW
System Boiler
18kW
2018-present
ErP A
84 fault codes
<p>The Baxi 600 System 2 18kW is a system boiler from Baxi, available at 18kW output. Produced 2018-present.</p>
Baxi 600 System 2 18kW Fault Codes 84
Code
Description
Severity
Type
111
Maximum Flow Temperature Limit Reached (EcoBlue)
On Baxi EcoBlue boilers, code 111 indicates the maximum flow temperature limit has been reached —…
Medium
Engineer
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117
Water Pressure Too High
System water pressure has exceeded the safe maximum — likely above 2.9 bar. Do NOT add…
Medium
Engineer
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118
Water Pressure Too Low (EcoBlue)
On Baxi EcoBlue boilers, code 118 indicates system water pressure is too low (below 0.5 bar).
Low
DIY
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127
Legionella Protection Temperature Not Reached
The boiler attempted a legionella prevention cycle (periodic high-temperature DHW heating) but could not reach the…
Low
Engineer
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162
Air Pressure Switch Fault (EcoBlue)
On Baxi EcoBlue boilers, code 162 indicates the air pressure switch has a fault — it…
High
Engineer
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166
Air Pressure Switch Fault (Secondary)
A secondary air pressure switch fault on Baxi EcoBlue boilers.
High
Engineer
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2 RED FLASHES
Boiler Overheat Tripped (EcoBlue/MainEco)
On Baxi EcoBlue and MainEco boilers, 2 red flashes indicates the overheat thermostat has tripped.
High
Engineer
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270
Dry Fire / No Water Circulation
The boiler has detected firing without adequate water circulation — a 'dry fire' condition. The pump…
High
Engineer
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3 GREEN FLASHES
Temporary Flame Loss (EcoBlue/MainEco)
On Baxi EcoBlue and MainEco boilers, 3 green flashes indicates a temporary flame loss. The boiler…
Low
DIY
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3 RED FLASHES
Ignition Failure — 5 Attempts (EcoBlue/MainEco)
On Baxi EcoBlue and MainEco boilers, 3 red flashes means the boiler has failed to ignite…
Medium
DIY
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4 RED FLASHES
Fan Fault (EcoBlue/MainEco)
On Baxi EcoBlue and MainEco boilers, 4 red flashes indicates a fan fault.
High
Engineer
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432
Earth Connector Error (EcoBlue)
The boiler has detected an issue with the earth connection in the electrical supply.
High
Engineer
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433
Heat Exchanger Overtemperature (EcoBlue)
The heat exchanger temperature has exceeded 95°C. This is a more severe overheat condition than the…
High
Engineer
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E.01-.04
Flame Lost 5 Times in 24 Hours (200/400)
On Baxi 200/400 boilers, E.01-.04 indicates flame has been lost 5 times within 24 hours while…
High
Engineer
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E.02-.07
No/Low System Water Pressure (200/400)
On Baxi 200/400 boilers, E.02-.07 indicates system pressure is below 0.5 bar.
Low
DIY
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E.04-.10
Failure to Light (200/400)
On Baxi 200/400 boilers, E.04-.10 indicates the boiler has failed to ignite — possibly a gas…
Medium
DIY
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E.04-.12
False Flame Signal (200/400)
On Baxi 200/400 boilers, E.04-.12 indicates a false flame signal is present — ionisation detected without…
High
Engineer
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E0
Temperature Sensor Fault (Avanta)
On Baxi Avanta boilers, E0 indicates a temperature sensor fault.
Medium
Engineer
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E1
Overheat (Avanta)
On Baxi Avanta boilers, E1 indicates the boiler has overheated. Try bleeding radiators first.
High
Engineer
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E10
Flow NTC Sensor Fault
The flow temperature sensor is giving an incorrect reading or has failed.
Medium
Engineer
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E109
Pre-Heating Circuit Fault
A fault has been detected in the pre-heating circuit. This affects the boiler's ability to provide…
Medium
Engineer
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E11
Return NTC Sensor Fault
The return temperature sensor is giving an incorrect reading or has failed.
Medium
Engineer
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E110
Boiler Overheat
The boiler has reached its maximum safe operating temperature and the safety thermostat has locked it…
High
Engineer
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E113
Condensate Trap/System Blocked
The condensate drainage system is blocked. This can occur when the condensate siphon is full after…
Medium
DIY
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E116
Flow Temperature Too High
The boiler flow temperature has exceeded its maximum safe level, triggering a high-temperature lockout.
High
Engineer
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E117
Gas Valve Error
The gas valve has detected a fault — it may not be opening, closing, or responding…
High
Engineer
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E118
Flame Without Demand
The boiler is detecting a flame signal when no heat demand exists — a safety-critical condition.
High
Engineer
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E119
Low Water Pressure
The most common Baxi fault code. System water pressure has dropped below 0.5 bar — the…
Low
DIY
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E12
DHW Sensor Fault
The domestic hot water temperature sensor has a fault. Relevant on combi boilers.
Medium
Engineer
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E125
Circulation Fault (Primary)
Water is not circulating properly through the primary heating circuit. Usually caused by a faulty pump,…
Medium
Engineer
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E128
Frequent Flame Failure
The boiler has lost its flame 12 times in succession, triggering a safety lockout.
High
Engineer
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E130
Overheat Thermostat Activated
The boiler's safety overheat thermostat has been triggered. The boiler has exceeded its safe operating temperature.
High
Engineer
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E131
Flue Overheat Lockout
The flue temperature has reached an unsafe level, triggering the flue thermostat.
High
Engineer
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E133
Ignition Failure / Frozen Condensate
The boiler has failed to ignite or there is a gas supply fault. In winter, this…
Medium
DIY
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E134
Gas Valve Relay Error
The gas valve relay has failed or is not responding correctly. The boiler cannot safely control…
High
Engineer
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E135
Airflow Fault / Air Pressure Switch
The air pressure switch is not registering correctly, preventing safe ignition.
High
Engineer
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E151
PCB Internal Fault
The Printed Circuit Board has detected an internal fault that cannot be reset by the user.
High
Engineer
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E154
Circulation Pump Fault
The central heating pump is not running or is not producing sufficient water flow. The boiler…
High
Engineer
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E160
Fan Fault
The boiler fan is not operating correctly — it may not be running, running too slowly,…
High
Engineer
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E161
Fan Fault (Secondary)
A secondary fan fault — the fan speed sensor or air pressure switch is giving an…
High
Engineer
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E164
Pressure Sensor Fault
The water pressure sensor is giving an incorrect or out-of-range reading.
Medium
Engineer
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E167
PCB Error
The Printed Circuit Board has a detected fault (non-lockout version).
Medium
Engineer
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E168
PCB Fault / Lockout
The main Printed Circuit Board has detected an unspecified fault and locked the boiler out. This…
High
Engineer
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E169
Ignition Lockout (After 5 Attempts)
The boiler has failed to ignite after 5 attempts and locked out.
Medium
DIY
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E17
Return NTC Open Circuit
The return temperature sensor circuit is broken.
Medium
Engineer
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E180
Water Hammer / Circulation Noise
Noise from water circulation — kettling, banging or hammering sounds — indicating scale buildup on the…
Medium
Engineer
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E193
Return Temperature Sensor Fault
The return water temperature sensor has a fault in its wiring or has failed.
Medium
Engineer
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E2
Poor Circulation (Avanta)
On Baxi Avanta boilers, E2 indicates poor or no water circulation through the system.
Medium
DIY
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E20
Flame Failure — Lockout
The boiler failed to detect a flame after the ignition sequence, or the flame extinguished during…
Medium
DIY
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E215
Fan Overspeed
The boiler fan is running above its maximum rated speed. Indicates a fault with the fan…
High
Engineer
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E220
Gas Valve Failure to Open
The gas valve has received the command to open but has not done so — preventing…
High
Engineer
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E23
Diverter Valve Fault
The diverter valve is stuck or not switching between heating and hot water.
Medium
Engineer
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E24
Flame Lost During Operation
The flame was detected but lost during running.
High
Engineer
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E25
Rapid Temperature Rise
Flow temperature rising faster than safe limits.
High
Engineer
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E27
Pressure Sensor Fault
The electronic water pressure sensor is faulty.
Medium
Engineer
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E28
Frozen Condensate / Flame Failure (Winter)
Baxi specifically flags E28 as associated with frozen condensate pipes in winter, making it distinct from…
Medium
DIY
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E29
Outdoor Sensor Fault
The outdoor temperature sensor is disconnected or faulty.
Low
Engineer
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E3
PCB Fault (Avanta)
On Baxi Avanta boilers, E3 indicates a Printed Circuit Board fault.
High
Engineer
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E31
Frost Protection Active
The boiler is running frost protection cycles to prevent freezing.
Medium
DIY
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E32
Flame Detected After Shutdown
A flame signal is present when the gas valve should be closed.
High
Engineer
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E33
Combustion Quality Fault
The air/gas mixture is outside the permitted range.
High
Engineer
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E34
Mains Voltage Fault
The mains supply voltage is outside acceptable range.
Medium
Engineer
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E4
Ignition Failure (Avanta)
On Baxi Avanta boilers, E4 indicates ignition failure.
Medium
DIY
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E40
Return Temperature Sensor Fault
The return water temperature NTC sensor has developed a fault. It may have an open circuit…
Medium
Engineer
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E50
Flow Temperature Sensor Fault
The flow water temperature NTC sensor has developed a fault. The boiler cannot accurately measure the…
Medium
Engineer
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E501
eBUS/Communication Fault
A communication fault between the boiler and a connected external controller (thermostat, zone control, etc.) over…
Medium
Engineer
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E53
Condensate Pipe Frozen / Blocked
Baxi's explicit condensate blockage code. Shown when the internal condensate system detects a backup caused by…
Medium
DIY
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E55
Fan Speed Fault
The fan is running outside its normal speed range — either too fast or too slow.…
High
Engineer
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E78
Water Pressure Sensor Fault
The electronic water pressure sensor is giving an incorrect reading. The boiler cannot verify the system…
Medium
Engineer
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E83
Flow/Return Differential Error
The temperature difference between the flow and return is outside the expected range. This usually indicates…
Medium
Engineer
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E84
Flow/Return Sensor Implausible
The flow and return temperature sensors are giving readings that are logically impossible, such as the…
Medium
Engineer
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E92
Combustion Error
The combustion quality is outside the permitted range. The air/gas mixture is not correct for safe…
High
Engineer
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H.01-.05
Flow/Return Temperature Difference Too High (200/400)
On Baxi 200 and 400 series boilers, code H.01-.05 indicates the temperature difference between flow and…
Medium
Engineer
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H.01-.08
Flow Temperature Rising Too Fast (200/400)
On Baxi 200/400 boilers, H.01-.08 indicates the flow temperature is increasing too quickly — insufficient circulation…
Medium
Engineer
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