What does E10 mean on a Wilo pump?

E10 on Wilo Stratos, Yonos MAXO, and Wilo-Star pumps indicates a winding overcurrent / overload trip — the electronics measured motor current above the trip threshold and shut the pump down to protect the windings. Common root causes are debris jamming the impeller, a seized rotor after a long idle period, viscous fluid (low water temperature with high glycol concentration), or shorted motor windings. Spin the rotor by hand via the vent screw; if it turns freely after a power-cycle and the pump runs without retripping, the fault was a transient blockage. Persistent E10 with a free-spinning rotor points to a control-card or winding fault — replace the head.

How do I reset a Wilo pump fault?

Most Wilo high-efficiency pumps (Stratos, Yonos MAXO, Stratos PICO) auto-retry up to 5 times before latching the fault. To force a manual reset: power-cycle the pump at the breaker for 60 seconds, then re-energise — the LED ring should clear and resume the previous mode. For BMS-connected pumps with E50, also re-establish the Modbus / BACnet connection or the fault relatches. Latched safety faults like E21 (blocked motor) and E25 (commutation) require physical inspection before reset; never bridge or bypass a latched fault to keep the pump running.

What's the difference between E10 and E20 on a Wilo Stratos?

E10 is winding overcurrent — the motor pulled more amps than the controller allowed, typically because the rotor is mechanically restricted or windings are degrading. E20 is winding overtemperature — the integrated thermal sensor inside the stator measured temperature above the trip threshold, usually because the pump is running into a closed valve (no flow to remove heat), the fluid temperature is too high (Stratos rated for −10 to +110 °C medium temperature), or the ambient temperature around the pump head exceeds 40 °C. E10 trips quickly under load; E20 trips after sustained operation under poor cooling. Both clear automatically once the underlying condition is resolved.

Wilo TOP-S vs Yonos MAXO error codes — same?

Mostly yes, with one important caveat. The Yonos MAXO, Stratos MAXO, and Wilo-Star Z product lines share the modern E10–E70 numeric fault codes documented across Wilo's current installation manuals. The older TOP-S, TOP-SD, and TOP-Z three-speed glandless pumps predate the unified electronic fault scheme — they use a green/red LED on the terminal box (red = winding overtemperature, no further granularity) plus an external thermal-protection contactor for restart logic. If you have a TOP-S throwing a code on a digital display, you're looking at a Wilo-Stratos retrofit head, not the original TOP-S electronics.

What does E11 mean on a Wilo pump and how do I fix it?

E11 on Wilo glandless pumps indicates dry running — the integrated dry-run sensor or pressure-loss detection has determined there is no fluid in the volute. Common causes are a closed isolation valve upstream of the pump, a system that hasn't been bled after refill, an air pocket in a horizontal pipe run, or a leaking expansion-vessel diaphragm that drained the system below the pump suction. Open all isolation valves, bleed the system at the highest point, top up to the correct fill pressure (typically 1.0–1.5 bar cold for residential heating), and power-cycle the pump. Persistent E11 after a verified bleed points to a failed vessel or hidden leak.

What does E21 mean on a Wilo Stratos or Yonos pump?

E21 indicates the motor is mechanically blocked — the controller commanded rotation, did not see the expected back-EMF feedback, and latched the fault to prevent winding damage. The most common cause on residential heating systems is sediment or magnetite buildup wedging the rotor between the stator and rotor can after a long summer idle period. Recovery: power down at the breaker, remove the vent screw on the front of the pump head, insert a flat screwdriver into the slot on the end of the rotor shaft, and rotate it back and forth until it spins freely. Refit the vent screw, repower, and run the pump on max. If E21 returns within 24 hours, magnetite contamination is significant — a system flush and a magnetic dirt-separator are required.

What does Wilo E50 mean?

E50 indicates a communication fault on the BMS / building-management bus — the pump expected a periodic heartbeat from the Modbus, BACnet, LON, or PLR master and timed out. On standalone pumps configured for analogue 0–10 V control or simple on/off relay control, E50 usually means the bus protocol is enabled in the pump menu but no master is connected. Causes: severed bus cable, terminator missing on the last device in the bus chain, slave-address conflict with another Wilo pump on the same bus, or BMS controller offline. The pump continues to run on its last commanded setpoint while E50 is active so heating is not interrupted; clear the fault by restoring bus communication or disabling the bus interface in the menu.

What does E70 mean and is it field-repairable?

E70 is an internal control-unit fault — the electronics card detected a self-test failure, an EEPROM checksum mismatch, or a hardware abnormality on the PCB itself. Unlike E10–E50 which point to system-side conditions a technician can fix, E70 indicates the head electronics need replacement. Power-cycle once to confirm it isn't a transient EMI event, but if E70 returns the only field repair is a replacement pump head (Wilo sells the head as a service kit on Stratos and Yonos MAXO; on smaller Wilo-Star units the whole pump is replaced). Do not open the electronics housing — the rotor magnets and capacitor bank store dangerous energy, and breaking the seal voids the IP rating.

Wilo fault codes Fehlercode — are German and English codes the same?

Yes. Wilo is a German manufacturer (headquartered in Dortmund) and its electronics are developed once for the global market — the E10, E11, E20, E21, E25, E30, E36, E50, E70, E71 numeric codes are identical on US, EU, UK, and APAC product variants. Only the displayed text translation differs: the German manual says 'Wicklungsüberstrom' for E10 where the English manual says 'winding overcurrent'. The Wilo Service Tool app (iOS / Android) auto-detects locale and shows the corresponding text. Cross-reference against the wilo.com installation and operating instructions for your specific model — codes carry the same meaning whether you see them on a Stratos in Munich or in Cleveland.

When should I replace a Wilo pump head versus repairing it?

Replace the head if: E70 returns after a power-cycle (electronics fault, no field repair), E10 persists after a verified free-spinning rotor (winding degradation), or the integrated electronics housing shows water ingress, scorch marks, or a swollen capacitor. Field repair is appropriate for: E11 (dry-running — bleed and refill), E20 / E21 (overheating or blocked rotor — clear airflow / free the rotor), E25–E36 (commutation / module faults that often clear after a power-cycle), and E50 (bus communication — restore the BMS link). Wilo sells most Stratos and Yonos MAXO heads as replaceable service modules so the wet end (volute, isolation valves, flange gaskets) stays in place and the system doesn't need to be drained.

HVAC

Wilo error codes, decoded.

Look up any Wilo fault code below. Each one is grounded in Wilo's own service documentation — the meaning, the symptoms, the causes, and the steps to clear it.

Quick answer

Wilo glandless circulation pumps (Stratos, Yonos, Wilo-Star, TOP-S/Z) report faults as E-codes on the LED bar or display. The most common are E10 (winding overcurrent / overload), E11 (dry running), E20 (winding overtemperature), E21 (motor blocked), E50 (BMS bus communication loss), and E70 (internal control unit fault). Codes are universal across Wilo's residential and commercial product lines worldwide.

By Nichita Herput

Co-founder & CEO · Reviewed May 2026

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Wilo sits in our HVAC coverage. Every page here is transcribed from the manufacturer's manuals, not scraped from forums.

What error codes does Wilo display?

Tap a code for the full breakdown — meaning, symptoms, causes, and fix steps.

E10

Winding overcurrent / overload — spin rotor via vent screw, replace head if it persists with a free rotor

E11

Dry running — open isolation valves, bleed at highest point, verify fill pressure 1.0–1.5 bar

E20

Winding overtemperature — confirm flow path is open, check fluid temp ≤110 °C and ambient ≤40 °C

E21

Motor blocked — use the vent-screw slot to rotate the rotor; recurring E21 indicates magnetite contamination

E25

Contact / commutation fault — power-cycle to retry; persistent E25 indicates Hall-sensor or driver IC failure

E30

Module overtemperature — ambient around the electronics housing too high, clear obstructions and check ventilation

E36

Electronics module fault — power-cycle once; if it returns, the pump head needs replacement

E50

BMS bus communication fault — verify Modbus / BACnet wiring, terminator, and slave address uniqueness

E70

Internal control-unit fault — not field-repairable, replace pump head

E71

CPU watchdog / software error — power-cycle; recurring E71 indicates head replacement

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