Flue Fans: Combi Boiler Flue Fan Motor Selection and Replacement Guide

The flue fan is one of the most critical components at the heart of modern room-sealed and semi-room-sealed combi boilers. These motorized fans, which ensure that the flue gases produced by combustion are safely discharged outside, put the combi boiler completely out of service when they fail. In this guide, we at Yedepa.com cover in detail, for HVAC technicians and service technicians, what a combi boiler flue fan motor is, how it works, which models are compatible with which combi boilers and how to choose the right product.

What Is a Flue Fan? Its Role in the Combi Boiler

A flue fan (in the literature also called a flue fan, extractor fan or venturi fan) is an electric motor-driven component that discharges flue gases such as carbon monoxide, carbon dioxide and water vapor produced in the combi boiler's combustion chamber out through the sealed flue system. In modern condensing and room-sealed combi boilers, this is done not by natural draft but by forced air circulation. For this reason, when the flue fan motor does not run, the combi boiler locks out for safety and error codes such as "fan fault", "F04", "E04" and "A03" appear on the display.

A combi boiler flue fan motor consists of three main parts: the electric motor (usually between 35W and 75W), the scroll housing (mostly die-cast aluminum) and a plastic or metal impeller. The speed varies between 2600 RPM and 5600 RPM, and this value is determined by the BTU capacity of the combi boiler.

Technical Operating Principle of Flue Fans

When the combi boiler starts up, the flue fan motor runs first. The fan's rotation is detected by the air flow sensor (air pressure switch), and after receiving this signal the electronic board opens the gas valve and starts ignition. This sequence is vital, because if combustion starts without flue extraction, toxic gas builds up inside. That is why the flue fan is not only an extraction device but also a safety component.

The technologies used in fan motors generally fall into the following three groups:

Shaded-pole motors: These are classic AC motors, inexpensive and durable. They are common in the entry-level models of the Sit and Fime brands.
Capacitor-run asynchronous motors: These are higher-efficiency, quiet-running models. They are generally preferred at power ratings of 65W and above.
BLDC (brushless DC) motors: Modern motors that allow modulating operation in premium condensing combi boilers.

Flue Fan Types and Connection Types

The flue fan motors you will come across in the spare parts market differ in their physical mounting and electrical connection. To choose the right product, you need to compare the following criteria with the existing fan in the combi boiler:

Feature	Typical Values	Importance
Power (W)	35W, 47W, 48W, 65W, 75W	Must match the combi boiler capacity
Voltage	220-240V AC / 50Hz	Turkish mains standard
Mounting type	2-leg screw-mounted, flanged, slide-in	Must be compatible with the scroll housing
Speed (RPM)	2600 - 5600	Determines the air flow rate
Direction of rotation	Clockwise / counterclockwise	Wrong direction = blocked flue
Capacitor	1µF, 2µF, 2.5µF	On the motor or on the board

Which Model Should You Choose? Decision Guide

The right fan choice depends on the brand and model of the combi boiler. Below we list the matches most often encountered in the Turkish market:

For Baymak, Arçelik, Beko, Altus users, the Combi Boiler Flue Fan Motor NG40M 65W is the most common solution. This model is preferred especially as an equivalent of Baymak original spare parts from the last 10 years.
In Airfel, Daikin, Unical combi boilers, the SIT 2-Leg Screw-Mounted 48W (W960210021) model works as an exact fit.
For the Baxi Eco Classic Nova, Baymak Eco5, Airfel series, the Sit Combi Boiler Flue Fan Motor works as a direct replacement; no additional adapter is required.
In Bosch Classic and Junkers combi boilers, the Fime motor with code VGR0004724 65W is used; in older Bosch/Buderus models, codes VGR0112943 / VGR0004720 are used.
For the Alarko, Herman, Sanica brands, the 47W Fime Flue Fan Motor is a standardized equivalent.
In Vaillant, Demirdöküm, Heatline, Vizo 24/28 series combi boilers, the Fime VGR0114934 is the most common spare part.
In Ariston and Chaffoteaux combi boilers, the 35W Fime Flue Fan Motor directly replaces the original one-to-one.
The Ferroli Domicompact F30 series uses a specially molded Fime motor; replacement with another model is not recommended.

Flue Fan Motors Available at Yedepa.com

At Yedepa.com, we keep in stock originally manufactured Sit and Fime flue fan motors for all major combi boiler brands. Our most popular models are listed below:

Combi Boiler Flue Fan Motor NG40M 65W – Compatible with Baymak, Arçelik, Beko, Altus (manufactured by Sit)
SIT 2-Leg Screw-Mounted 48W (W960210021) – Compatible with Airfel, Daikin, Unical
Sit Flue Fan Motor – For Baxi Eco Classic Nova, Baymak Eco5, Airfel
Fime VGR0004724 65W – Compatible with Bosch Classic and Junkers
Alarko – Herman – Sanica 47W Fime Flue Fan Motor
Fime VGR0114934 – Compatible with Vaillant, Demirdöküm, Heatline, Vizo 24/28
Ariston – Chaffoteaux 35W Fime Flue Fan Motor
Fime VGR0112943 / VGR0004720 – Compatible with Bosch, Junkers, Buderus
Ferroli Domicompact F30 Fime Flue Fan Motor
Bosch Junkers 3000W Fime Flue Fan Motor

All our products are shipped in original Sit and Fime packaging; we do not sell counterfeit or locally made copy products.

About the Sit and Fime Brands

Sit Group, headquartered in Italy, is one of the world's longest-established manufacturers of components for combi boilers and gas-fired appliances. Operating since 1953, the company is the OEM supplier of gas valves, flue fans and electronic control boards to many major brands. In Turkey, Sit products are used in the original equipment of brands such as Baymak, Airfel and Baxi.

Fime, also of Italian origin, is a brand specialized in the manufacture of flue fan motors. The motors used as original spare parts by many major combi boiler manufacturers such as Vaillant, Bosch, Junkers, Ariston, Ferroli and Demirdöküm are produced by Fime. All Fime products sold at Yedepa.com are of Italian origin and carry serial numbers.

Professional Selection Criteria

As an HVAC technician or technical service company, when choosing a flue fan motor we recommend that you follow the steps below:

Read the label on the old fan: The manufacturer code on it (Sit or Fime code) is the most reliable matching criterion. Even if the brand logo has worn off, the code engraved on the motor body is permanent.
Verify the voltage and power rating: A product other than 220V – 50Hz is not suitable for the Turkish mains. The wattage difference should not exceed 15%.
Check the mounting type: The 2-leg screw-mounted, 3-leg flanged or slide-in type must be compatible with the combi boiler. Using an adapter creates a safety risk.
Check the capacitor location: In some combi boilers the capacitor is on the fan, in others it is on the electronic board. The wrong choice causes the motor to burn out.
Verify the direction of rotation: The clockwise (CW) or counterclockwise (CCW) information is given on the label. The wrong direction reverses the flue draft.

Flue Fan Failure Symptoms

The following symptoms usually indicate that the flue fan motor needs to be replaced:

The combi boiler turns on but shuts down with an error after a few seconds (F04, E04, A03, etc.)
A metallic buzzing, rubbing or humming noise comes from the fan motor
Play is felt in the bearings when the fan impeller is turned by hand
The air flow sensor (pressure switch) makes a "click" sound at regular intervals
When you open the combi boiler cover, the fan motor housing is hotter than normal
Vibration or irregular air flow occurs in the flue pipe

When two or more of these symptoms are seen together, replacing the motor is the safest solution. Trying to fix it only by replacing the capacitor usually provides a temporary improvement; afterwards the motor may burn out completely.

Usage and Maintenance Recommendations

A combi boiler flue fan motor is designed to run trouble-free for an average of 8-12 years. To extend this service life, we recommend the following maintenance steps:

During the annual combi boiler service, the fan blades must always be cleaned with a soft brush. Soot buildup on the blades leads to imbalance and bearing wear.
The condensate drain must not be blocked; if condensate leaks into the fan motor, a short circuit occurs.
The external flue terminal must be free of bird nests, leaves or covers. Back pressure causes the motor to overload.
The electrical contacts must not be oxidized, and the cable socket must be fully seated. A loose contact burns out the motor winding.
Before fitting the replacement motor, disconnect the combi boiler's power at the mains; switching it off only with the combi boiler's button is not enough.

Points to Note During Replacement

Flue fan motor replacement must always be carried out by an authorized HVAC technician. Flue work by home users both voids the warranty and leads to serious safety risks such as carbon monoxide poisoning. For professional technicians the typical replacement time is 20-40 minutes, following this sequence:

The combi boiler is disconnected from the mains power supply, and the gas valve is closed.
The front cover and the sealing gasket are removed.
The fan motor's electrical socket and the air pressure switch hose are disconnected.
The screws on the scroll housing (usually 4) are removed and the fan is taken out as a complete assembly.
The new motor is mounted in the same orientation and the socket is reconnected.
The gasket is replaced (this is very important, especially in condensing combi boilers).
The combi boiler is put into operation and a flue draft test (with an analyzer) is carried out.

Frequently Asked Questions (FAQ)

1. If my flue fan motor burns out, can I run the combi boiler temporarily without the fan?
No. Room-sealed combi boilers must never be operated without a flue fan; there is a risk of carbon monoxide poisoning. The combi boiler already shuts itself down with its safety lockout.

2. What is the difference between Sit and Fime?
Both are of Italian origin and are OEM suppliers. Sit is used mainly in the original equipment of the Baymak/Airfel/Baxi group, while Fime is used in the original equipment of the Vaillant/Bosch/Ariston/Ferroli group. They are considered equivalent in terms of quality.

3. Can I fit a 75W fan motor instead of a 65W one?
Not recommended. If the wattage difference exceeds 15%, the combi boiler's air flow sensor cannot receive the correct signal and the electronic board gives an error. The best practice is to stick to the old label.

4. How long does delivery of a fan motor take?
For Yedepa.com in-stock products, shipments are dispatched on the same business day. Delivery times across Turkey vary according to the courier company's route.

5. How do I check the direction of the motor I bought?
The arrow on the motor body shows the direction of rotation. Compare it one-to-one with the old motor; in case of a mismatch you can request an exchange.

6. What is the warranty period?
All Sit and Fime flue fan motors sold at Yedepa.com come with a manufacturer's warranty. The warranty terms are explained in detail on the product page.

Conclusion: Yedepa.com Advantages

Choosing the right flue fan motor is the most critical factor for the safe and long-lasting operation of the combi boiler. At Yedepa.com, we offer the following advantages to HVAC technicians, authorized service centers and technical maintenance companies in Turkey:

Original Sit and Fime products – Of Italian origin, serial-numbered, packaged.
Extensive compatibility database – Which model fits which combi boiler is clearly listed on the product page.
Technician- and service-oriented pricing – Special tiered discounts apply to B2B purchases.
Technical support – Our expert team helps by phone in choosing the right product.
Secure payment and fast shipping – The same standard of service to every part of Turkey.

When you need a combi boiler flue fan motor, you can visit the flue fans category at Yedepa.com and shop with confidence by confirming your combi boiler's brand in the compatibility list on the product pages. The right part, the right service and the right supplier: Yedepa.