Overview
The E125 error on a Baxi EcoBlue boiler indicates a water circulation fault — the boiler has detected poor or no circulation of heating water. Common reasons are low system pressure, airlocks in the heating circuit, a blocked or sludged system, a faulty circulation pump, a leaking pressure relief device or pipework, or an electrical/control fault that stops the pump from running. When the boiler senses inadequate flow it will often shut down or lock out as a protective measure. Severity ranges from low to high depending on cause. If it is caused by low pressure or trapped air it can often be fixed quickly by a homeowner; however, if the pump has failed, there is sludge/blockage in the heat exchanger or pipework, or there is a leak or electrical fault, the issue usually needs a qualified engineer. Leaving a circulation fault unaddressed can lead to poor heating and hot water, further component strain, or repeated lockouts, so it should be diagnosed promptly. Some basic checks and simple actions (repressurising, bleeding radiators, visual leak inspection, reset) are suitable for a competent homeowner, but anything requiring access inside the boiler casing, replacement of the pump, electrical testing, or work on gas or sealed components must be carried out by a Gas Safe registered engineer.
Possible Cause: Water circulation fault
Troubleshooting Steps
Safety first:
1) Before doing anything switch the boiler off at the programmer and the boiler power switch, and allow the system to cool. If you find any leak or smell gas, stop, turn off the mains water to the system if safe to do so and call a Gas Safe engineer immediately. Do not remove the boiler casing or attempt repairs to gas, electrical or sealed components.
Initial checks a homeowner can do:
1) Check the pressure gauge on the boiler. For most Baxi boilers normal cold pressure is around 1.0–1.5 bar. If the pressure is significantly below 1.0 bar this can cause E125.
2) Look for visible leaks around the boiler, radiators and pipework and check the condensate/pRL discharge pipe for signs of water. Any leak requires an engineer.
3) Listen to the boiler when it runs: gurgling, knocking or a pump grinding noise can indicate air, blockages or a failing pump.
4) Check that radiator thermostatic valves and the room thermostat are open and set correctly — incorrect valve positions can mimic circulation problems.
How to repressurise (general guidance — follow your boiler manual):
1) Locate the filling loop (usually a braided hose with valves) and the boiler pressure gauge. Ensure both valves on the filling loop are closed before connecting or opening.
2) With the boiler isolated and cold, slowly open the filling loop valve(s) until the pressure rises to about 1.0–1.5 bar. Close the valve(s) and remove/secure the filling loop as instructed in your manual.
3) Recheck for leaks after repressurising. If pressure drops again quickly, do not keep topping up — that indicates a leak or PRV fault and you must call an engineer.
Bleeding radiators to remove airlocks:
1) Turn the heating off and let the system cool. Use a radiator key to open the bleed valve at the top of each radiator (start with the radiator nearest the boiler). Have a cloth and small container ready.
2) Turn the valve anti-clockwise until air hisses out, then when water flows steadily close the valve. Work through all radiators and then recheck boiler pressure and top up if needed.
3) Restart the boiler and check whether radiators heat evenly. If you still have cold spots or gurgling, an airlock or sludge may remain.
Checks related to the pump and flow:
1) If the boiler is cold and you can safely access pipework, carefully feel the flow and return pipes to the radiators when the heating is on (they will be hot if flow is present). If the flow pipe is cold or both pipes are only lukewarm, circulation is inadequate.
2) Listen at the pump for running noise. A completely silent pump when the boiler is calling for heat, or loud grinding, indicates pump failure — do not attempt internal repairs; call an engineer.
When to reset:
1) After you have completed the checks above (repressurised, bled radiators, corrected any obvious valve settings) try the boiler reset per the manual. If the fault clears and the system runs normally, monitor pressure and performance.
When to call a professional (must-call situations):
1) If the E125 persists after you have checked pressure, bled radiators and performed a safe reset.
2) If you find a leak, repeated pressure loss, visible corrosion, PRV discharge, or if repressurising does not hold.
3) If the pump appears to have failed (no running noise when heating should be on) or is making loud/unusual noises.
4) If you suspect sludge/blockage, need powerflushing, or the fault is related to electrical/PCB or gas components. Any work requiring removal of the boiler casing, replacement of the pump, electrical testing or gas-safe work must be done by a Gas Safe registered engineer.
Notes and cautions:
1) Do not keep running the boiler if it’s overheating, making abnormal noises, or if there is leaking water — isolate and call an engineer.
2) Do not attempt internal repairs, dismantle the pump, or work on gas/electrical parts yourself.
3) Keep a record of what you tried and any symptom details (pressure readings, noises, which radiators are cold) to give to the engineer — this speeds diagnosis.
If your checks do not clear the E125 or if you are uncomfortable performing any step, contact a Gas Safe registered heating engineer. They can carry out safe diagnostics (pump testing/replacement, powerflush, PRV and heat exchanger inspections, electrical fault finding) and repair the underlying cause.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi EcoBlue.