What does the fault code F.75 mean in Wilo?

Pump fault/lack of water: when the pump starts, a sufficient pressure increase is not detected. If the Wilo UNRS15/5-3 P pump is blocked, rotating slowly, or without power, the pressure sensor does not detect the increase and the boiler enters F.75; check power supply to the pump, bleed, and consult d.149 (substates: 1=blocked pump, 2=electrical error, 3=dry running, 6=no response, 7=incorrect pump).

What does fault code E125 mean in Wilo?

Circulation fault in the primary circuit. If the Wilo UNRS15/5-3 P pump does not rotate or is seized, there is no flow and the unit detects overtemperature/gradient; check voltage to the pump, unblock via the front cap, and confirm there is circulation.

What does the code A1 281 mean in Wilo?

Blocked pump or operating with air (the heating pump does not generate pressure). If the Wilo UNRS15/5-3 P pump is blocked or has air, it does not generate pressure and the boiler locks with A1 281; bleed the circuit and check that the rotor spins and receives power.

RefurbishedWilo Pumps

Wilo Circulating Pump UNRS15 5 3 P Ref. 4509739

Name: Wilo Circulating Pump UNRS15 5 3 P Ref. 4509739
Brand: Wilo
SKU: BWUNRS15
Price: 55 EUR
Availability: InStock

55 €VAT includedIn stock · 1 unit

Circulating pump: refurbished spare part that circulates water in the heating circuit. Useful if there is noise, water is not circulating, or radiators do not heat evenly. Reference 4509739. Includes a one-year warranty and delivery within 2–4 working days in the EU.

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Delivery in 2–4 working days

1-year warranty

14-day return

Technical support

Key Data

Reference: 4509739
Brand: Wilo
Type of part: Pumps
Available units: 1 unit in stock
Status: Refurbished
Warranty: 1 year
Shipping: 2–4 working days (EU)
Return: 14 days

Fault codes related to this part (not the entire boiler). They usually have more possible causes: first rule out electrodes, wiring/connections, and gas supply. Verified with ≥3 sources.

Code	What does it mean?	Cause and diagnosis (this part)
F.75	Pump fault/lack of water: when the pump starts, a sufficient pressure increase is not detected.	If the Wilo UNRS15/5-3 P pump is blocked, running slowly, or without power, the pressure sensor does not detect the increase and the boiler enters F.75; check power supply to the pump, bleed, and consult d.149 (substates: 1=pump blocked, 2=electric fault, 3=dry running, 6=no response, 7=wrong pump).
E125	Circulation fault in the primary circuit.	If the Wilo UNRS15/5-3 P pump does not rotate or is seized, there is no flow, and the unit detects overtemperature/gradient; check the voltage to the pump, unblock it via the front cap, and confirm there is circulation.
A1 281	Pump blocked or operating with air (the heating pump is not generating pressure).	If the Wilo UNRS15/5-3 P pump is blocked or has air, it does not generate pressure and the boiler locks with A1 281; bleed the circuit and check that the rotor turns and receives power.