Main Eco Compact E125 fault code: water circulation fault
The Main Eco Compact E125 fault code means “Water circulation fault” in Baxi’s current error-code table. The Main Eco Compact manuals describe it as a primary circulation fault. The current manufacturer table includes Main Eco Compact Combi and Main Eco Compact System boilers in the model group for this code.
E125 says the boiler is not seeing the expected temperature response from water moving through its primary heating circuit. It does not prove which part is responsible, and it is not an instruction to open the boiler or alter its pump, valves or internal vents.
What does E125 measure?
The Main Eco Compact System installation and service manual gives useful detail. It says E125 can be displayed in either of two situations:
- between 15 and 30 seconds after the burner lights, the primary water temperature has not changed by 1°C; or
- within 10 minutes of the burner lighting, the actual primary temperature twice exceeds the selected temperature by 30°C.
The manual says these situations indicate poor primary circulation. In plain English, the boiler is checking whether the heating water responds as expected after firing. Too little change, or an excessive rise compared with the selected temperature, can both point to heat not being carried away in the expected way.
What is the primary heating circuit?
The primary circuit is the sealed water circuit that carries heat from the boiler through the heating system. On a combi, it is separate from the fresh water that comes from a hot tap. On a System boiler, it also transfers heat to the separate hot-water cylinder through the system arrangement.
E125 is not the same as low mains pressure at a tap or the E118 low-system-pressure code.
What you may notice
With E125, you might find:
- the boiler starts, then locks out;
- radiators stay cold or warm unevenly;
- heating works briefly before stopping;
- hot water is interrupted on a combi;
- the fault appears during a longer heating demand;
- the boiler makes a new water-movement or mechanical sound;
- E125 returns after a reset; or
- another code appears before or after it.
If your boiler appears to run but radiators remain cold, [boiler running but radiators not heating](/boiler-help-heating-on-no-radiators/) gives safe external checks. For a wider explanation of uneven radiators, [radiator not working](/boiler-help-radiator-not-working/) helps record the location of cold areas without opening the boiler.
Does E125 apply to every Main boiler?
No. Fault-code meanings depend on the exact range. Baxi’s current table lists E125 for a group that includes Main Eco Compact Combi and Main Eco Compact System. The Main Eco Compact manuals also use the primary-circulation wording.
Confirm the complete model name and copy the whole code exactly. Do not assume E125 has the same meaning or reset behaviour on an unrelated Main boiler.
Safe observations before a repair
Leave the casing closed. You can record:
- The exact code and model. Photograph the display if convenient.
- What was running. Note whether the fault appeared during heating, hot-water use or both.
- How long the boiler ran. Record whether E125 appeared immediately or after several minutes.
- Radiator behaviour. Note which radiators warmed and where they felt cold.
- The visible pressure. Record the reading without changing it solely because E125 is shown.
- Any new sound. Describe when it begins and stops rather than trying to locate it internally.
- Recent work. Mention radiator bleeding, draining, a replaced radiator, valve work or system maintenance.
- Other messages. Preserve the order of any additional codes.
What not to do
Do not attempt to restore circulation by working on the boiler. Avoid:
- removing the casing;
- trying to free, bleed or test the pump;
- opening internal vents or hydraulic fittings;
- adjusting a bypass or concealed valve;
- changing pump settings;
- draining or refilling the system as an experiment;
- adding cleaning chemicals or leak sealer in response to the code;
- testing temperature sensors, wiring or circuit boards; or
- repeatedly resetting the appliance.
Is E125 caused by low pressure or air?
E125 itself confirms a circulation problem, not a specific cause. Low system pressure has a separate manufacturer code, and the display does not prove that air is present.
Record the pressure and tell the engineer about recent radiator work, but do not add water or start bleeding radiators solely because E125 appears. Those actions may be appropriate in a different, clearly identified situation, but they can change the evidence or create another issue here.
Likewise, the word “circulation” does not prove the pump has failed. Flow can be affected by different conditions, and the fault must be tested rather than guessed.
Can I reset E125?
The Main Eco Compact installation manual includes E125 among the codes that may be reset. The user guide explains that only faults showing the R symbol are user-resettable; a spanner symbol means the user should contact support.
If your exact display shows R and the exact model guide allows it, one reset is reasonable when there are no safety warning signs. If the reset has no effect or E125 returns, stop. The manufacturer manual says regular reappearance requires further investigation.
Do not keep resetting the boiler to obtain short bursts of heat. Repeated lockouts mean the circulation condition has not been resolved.
When E125 needs professional repair
Arrange a repair if:
- E125 remains after one permitted reset;
- it returns during heating or hot-water demand;
- radiators do not heat normally;
- the boiler repeatedly starts and stops;
- a new noise appears;
- the fault began after system work; or
- any other code is displayed.
An engineer can check temperatures, circulation and the control sequence with appropriate equipment, then repair the actual fault rather than replacing parts by assumption.
Important safety warning
If you smell gas, avoid electrical switches and naked flames, leave the property and call 0800 111 999 from a safe place. If a carbon-monoxide alarm sounds or anyone feels unwell, move into fresh air, seek medical help and do not use the boiler until it has been checked by a Gas Safe registered engineer.
Fix the E125 fault and get dependable heating and hot water back.
Quick Answers
What does Main Eco Compact E125 mean?
It means the boiler has detected a water-circulation fault in the primary heating circuit.
Does E125 mean the pump is broken?
No. Poor circulation has been detected, but the code does not identify one failed part.
Is E125 the same as low boiler pressure?
No. Main Eco Compact low pressure has a separate code. Record the pressure, but do not add water solely because E125 is showing.
Should I bleed the radiators?
Not as an automatic response to E125. Record recent radiator work and leave fault-finding to an engineer.
Can I reset E125?
If the exact display shows the R symbol and the exact model guide permits it, try once. If the code returns or the reset has no effect, arrange repair.
Is E125 safe to ignore?
No. It can stop reliable heating and may involve abnormal temperature behaviour. Repeating lockouts need investigation.
Do I need an engineer?
Yes if the code remains, returns, affects heating or hot water, or appears with another fault.