Baxi E125 fault codewhat it means and how to fix it
Baxi's primary circulation fault, decided by two temperature tests the manuals spell out. Pump, air or a blocked filter; the pressure is usually fine.
Take care
Get a Gas Safe registered engineer to look at your Baxi E125
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Can you hear or feel the pump?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Nothing — no hum, no vibration
The pump is not running. Seized, or not being fed by the board.
Engineer job. On the 600 and 800 the flow checks for 230 V at the pump connector before condemning it.
It hums but the radiators stay cold
Running but not moving water: air in the pump or an obstruction. The two things Baxi's flow says to check.
Bleed the system; if that does not clear it, an engineer will vent the boiler and check the filter and pump.
It started after a radiator was changed or the system drained
Almost certainly air. Baxi's user guide says the de-aeration function must be repeated after any partial drain.
Bleed all radiators, check the pressure, reset once on a digital-display boiler.
What E125 means
E125 is "Circulation Fault (Primary Circuit)" on the selector-switch Baxis and "Circulation fault (primary)" on the digital-display ones, and Baxi are unusually specific about how the board decides it has one. The Duo-tec Combi HE A manual: "E125 is displayed in either of two situations: i) If within 15 seconds of the burner lighting the boiler temperature has not changed by 1°. ii) If within 10 minutes of the burner lighting the boiler temperature twice exceeds the selected temperature by 30°. In these instances poor primary circulation is indicated." The 600 and 800 manuals keep both tests and widen the first window to "between 15 and 30 seconds".
Two opposite symptoms, one diagnosis: no temperature change means the water at the sensor is not moving; repeated overshoot means it is moving too slowly to carry the heat away. What the reader should do differs by generation. On the Duo-tec HE and Platinum the user guide puts E125 among the codes that "indicate faulty components. You should make a note of the displayed error code and contact your installer or service engineer" — no reset is offered.
On the 600, 800 and Compact it is in the list of codes relit by "pressing the Reset button for 1 to 3 seconds". The 600 Combi fault-finding flow for 109 and 125 is short: "System fault — correct. Ensure that the boiler and system are fully vented. Check flow temperature sensor connections and position", with the sensor's cold resistance given as about 10 kΩ at 25 °C. Pressure is not on that list, because a system can be at 1.5 bar and still not circulating.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump failed or running slow | The most common cause on a boiler over eight years old. Baxi's pump on the 600 and 800 is part 7684006 and the head alone (7686336) can be changed on some; a failing pump often hums without turning. | Common |
| Air in the boiler or system | Baxi's stated remedy is to ensure the boiler and system are fully vented. Air at the top of the heat exchanger or in the pump housing stops flow past the sensor even with the pump spinning. | Common |
| Blocked filter or sludged system | A magnetic filter that has not been cleaned, or a system without one that has sludged, strangles the flow the pump can deliver. Overshoot at the sensor is the typical result. | Common |
| Flow sensor connection or position | Baxi's flow checks the flow temperature sensor connections and position. A sensor that has come loose from its pocket reads slowly and the board sees "no change in 15 seconds" on a perfectly good system. | Occasional |
| Closed valves or a stuck diverter | Every radiator valve shut, a system isolation valve left closed after work, or a combi diverter that has not moved over to the heating port. The pump has nowhere to push. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£500
Time on site
1 hour
Bleeding costs nothing. Filter clean £60–£90 at a service. Pump head (Baxi 7686336) £150–£250 fitted; pump assembly (7684006) £200–£320. Power flush £300–£500.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 28 September 2026
Baxi / Potterton / Main NTC temperature sensor (flow, return or DHW)
7207471£18–£45Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main pump assembly
7684006£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main diverter valve motor
7216534£45–£95Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Baxi fault codes
- E110Stop — call an engineerThe safety thermostat has tripped on overheat — "overheat of the primary water" in Baxi's words. One reset is allowed on every generation. If it trips again, the water is not moving.Related: overheat and circulation
- E.04.08Stop — call an engineer"Maximum safe temperature value reached": the safety thermostat has opened on a Baxi 200/400 Combi or Combi 2. Circulation first, the thermostat second, in Baxi's own order. One reset, then an engineer.Related: overheat and circulation
- E.01.17Get it checked"No water circulation (permanent)" on the Baxi 200/400 Combi and Combi 2, after H.01.18 has shown as a temporary block. Pressure, venting and the pump, in Baxi's order; reset once.Related: overheat and circulation
- E109Get it checkedPre-circulation fault on the digital-display Baxis: the board could not confirm water moving before it would light the burner. Vent the system; Baxi allow a reset from the button.Related: overheat and circulation
- E270Get it checkedBaxi's dry-fire circulation fault: the heat exchanger was heating with too little water passing through it. Air, a stopped pump or a closed circuit; not a code to reset repeatedly.Related: overheat and circulation
- E193Get it checkedPre-circulation fault on the selector-switch Baxis (Duo-tec Combi HE, Platinum, Megaflo HE A), shown as E1 then 93. Baxi offer no reset for it; the pump or air is the cause.Related: overheat and circulation
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Common questions about Baxi E125
Can I reset E125?
On the 600, 800, Compact and Assure, yes — Reset for one to three seconds, and Baxi list 125 among the codes that relights. On the selector-switch Duo-tec HE and Platinum the user guide offers no reset for E125 and says to note the code and contact your installer.
The pressure is fine, so why a circulation fault?
Because E125 is a temperature test, not a pressure one. Baxi's board watches whether the flow temperature changes in the first seconds after ignition and whether it overshoots later. Plenty of water sitting still fails both tests.
What is the difference between E125 and E109 or E193?
E109 (digital display) and E193 (selector switch) are pre-circulation faults, decided before the burner lights. E125 is decided after ignition from the temperature response. Same underlying problem, different moment of detection.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.