Overview
Error code 111 on a Baxi EcoBlue typically means the boiler has detected the flow temperature has reached or exceeded its maximum allowed limit. In practice this means the boiler thinks the water leaving the heat exchanger and going to your central heating system is too hot. The fault can be caused by a genuine overheating condition (blocked flow, failed pump, closed valves or poor circulation), a user setting with the flow temperature set too high, or a faulty flow temperature sensor/thermistor or control electronics giving an incorrect reading. Severity is medium to high. An overheating condition can force the boiler to lock out to protect components and prevent unsafe operation. In some cases the fault is temporary and can be cleared by simple user actions (reduce flow temperature, reset). However, recurring errors or errors caused by failed components (pump, sensor, diverter valve, PCB) require a Gas Safe registered engineer. Do not attempt gas or internal electrical repairs yourself; initial checks and simple adjustments can be done by a homeowner, but replacement of internal parts must be performed by a qualified professional.
Possible Cause: Maximum limit of flow temperature
Troubleshooting Steps
Safety first
1) If you smell gas or suspect a gas leak, get everyone out of the property and call your gas emergency number immediately. Do not operate electrical switches or the boiler.
2) If the boiler shows any signs of fire, significant smoke, or burning smells, switch off electricity at the consumer unit and call emergency services.
3) For routine checks, you may switch the boiler off at its ON/OFF switch or isolator before inspecting external parts. Do not open the boiler casing or try to access internal components unless you are a Gas Safe engineer.
Initial checks a homeowner can do
1) Note the exact display and any lights or behaviour. Make a note or take a photo of the error code and any other messages before you reset.
2) Reduce the flow temperature using the heating/flow temperature control on the front of the boiler. Baxi guidance suggests 55°C as a typical efficient setting for combi boilers. Turn the knob down slowly and see if the error clears or the boiler runs normally.
3) Try a controlled reset of the boiler following the user manual: use the reset control or selector (hold for around 5 seconds if required). Do not repeatedly reset more than 2–3 times; if it returns immediately, stop and proceed to other checks.
4) Check system pressure on the pressure gauge. Cold central heating pressure should usually be around 1–1.5 bar. Extremely low or very high pressure can affect circulation and temperature control.
5) Check that radiators are turned on (thermostatic radiator valves open) and that zone valves (if present) are calling for heat. If all radiators are cold or there are cold spots at the bottom of radiators, bleed the radiators to remove trapped air and improve circulation.
6) Listen to the boiler/pump when it runs. The pump should make a humming/small vibration noise; if the pump is silent when the boiler is calling for heat, circulation may be failing.
Specific diagnostic and fix steps to try
1) Lower flow temperature then reset once. If the code clears and the heating works, leave the flow set lower and monitor for recurrence. If it only happens when the flow is set very high, keep it at a moderate temperature.
2) Bleed radiators and ensure TRVs or zone valves are open. Poor circulation can let the heat exchanger overheat.
3) Top up system pressure if it is low using the filling loop, following the user manual. If pressure is repeatedly low, you will need an engineer.
4) Check for recent changes or works to the system (pump replacement, pipework valves closed, recent servicing) that might have left a valve closed or changed flow paths.
5) If the pump seems not to run when the boiler is calling for heat, or if you hear strange banging/knocking, do not try to dismantle the pump. These are signs of a circulation fault and require a Gas Safe engineer to inspect and, if necessary, replace the pump or repair associated controls.
6) If the error persists after the simple steps above, it may indicate a failed flow temperature sensor (NTC/thermistor), a faulty diverter/zone valve, a blocked heat exchanger, or a PCB control fault. These are internal components; do not attempt repairs yourself.
When to call a professional
1) Call a Gas Safe registered engineer if the error returns after reset, if you cannot restore normal circulation, if the pump appears to have failed, or if the boiler locks out repeatedly. Also call an engineer if you are not comfortable performing the basic checks listed above.
2) Provide the engineer with the boiler model, serial number, the exact error code (111), what you did when the code appeared, the flow temperature setting, and any other symptoms (no hot water, cold radiators, noises, pressure changes).
3) Ask the engineer to check flow sensor operation, pump performance, diverter/zone valves and the heat exchanger, and to test the PCB and safety thermostats if required.
Other important notes
1) Avoid repeatedly resetting the boiler more than a couple of times; frequent resets can mask an ongoing fault and may cause more wear.
2) Lowering flow temperature can be a temporary mitigation, but if the boiler routinely overheats at normal settings you need a qualified repair to avoid future failures or safety risks.
3) Keep your service records and the error details; that information speeds diagnosis for the engineer.
Summary: try lowering the flow temperature to around 55°C, perform basic checks (reset once, check pressure, bleed radiators, ensure pump appears to run), and if the fault persists or you suspect a failed pump, sensor or internal component, contact a Gas Safe registered engineer to diagnose and repair the boiler.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi EcoBlue.