When a Fagor boiler displays error F3 (listed as F03 in the manual), it’s usually indicating a common low-pressure issue caused by a lack of water. This low pressure refers to the closed-loop heating circuit, not the open hot water circuit found in combination boilers. However, any technician knows that low pressure in a heating system can have different causes beyond just a lack of water.
In this article, you’ll find a full list of causes and solutions for the F3 error, organized clearly in a table for easy reference.
Fagor Spare Parts for Your Business at Suner
If you’re looking for Fagor boiler parts or components for other brands, you’ve come to the right place. Suner is a Spanish company with over 40 years of experience supplying boiler parts to industry professionals. We offer an extensive catalog of original Fagor parts.
Use the first link below to explore all available Fagor parts. Since this article uses the Fagor FEE models as examples, we’ve also included direct links to parts for those specific models:
- All Fagor Boiler Parts
- Parts for Fagor FEE 24 MA
- Parts for Fagor FEE 35 MA
Please note: Suner serves only industry professionals. We do not sell to the general public. At our physical locations, you’ll be assisted by trained staff, and our online store features a highly efficient search tool to help you find what you need. Orders placed before 5:30–6:00 PM will be delivered before 10:30 AM the next day.
When Does the F3 Error Appear?
This error usually shows up in two situations:
- During the boiler’s first startup, or what the manual calls “initial setup.” After plugging the boiler in and pressing the power button, the F3 error may appear. This happens because the heating circuit is empty. Once the circuit is filled with water, the error should disappear.
- Over time, due to normal use or evaporation, the water in the primary circuit may drop to a level where the boiler can’t function properly. In most cases, refilling the system resolves the issue.
Still, as explained in the next section, other factors can also trigger this error.
Causes and Solutions for Fagor Boiler F3 Error
| Cause | Solution |
| Low pressure from lack of water in the heating circuit (as stated in the manual). | Refill the system using the filling tap. Stop once the pressure gauge reads between 1 and 1.2 bar. |
| Repeated low pressure due to leaks in the boiler, pipes, or radiators. | Locate and fix the leaks. |
| Safety valve releasing water even when pressure is below 3 bar. | Replace the valve, as it should only activate above 3 bar. |
| Blocked or broken filling tap not allowing water in. | Check if water flows through the tap and replace it if necessary. |
| Low pressure combined with high temperature caused by a faulty circulation pump. | Unblock or replace the pump. |
| High temperature with low pressure due to air in the system. | Bleed the boiler and the heating circuit. |
| False error caused by a faulty pressure sensor. | Check the sensor connection or replace it. |
| Damaged control board causing communication issues. | Replace the electronic board. |
About Fagor and Its Isocomfort and Comfort Boilers
Fagor is a Spanish company based in the Basque Country with over 60 years in the appliance and heating industry. Since 2019, its home appliance division has been managed by the Polish multinational Amica. Fagor is known for its focus on energy-efficient and environmentally friendly products.
The Fagor Isocomfort (FEE) and Comfort (FE) boilers are both wall-mounted, sealed gas units that provide heating and instant domestic hot water. The main difference is that Isocomfort models use micro-accumulation technology for hot water, while Comfort models do not. Both are low NOx Class 5 boilers and can reduce emissions by up to 70%.