Ariston Air Pressure Switch (models MFFI/BFFI) - Ref. 605 99509
In the Ariston boilers from the MFFI/BFFI ranges, the Air Pressure Switch (Ref. 605 99509) is responsible for checking the air pressure and authorizing the operation of the boiler. If this part fails, you will notice that the boiler does not start or gets locked, even if the pressure is correct, and it may display fault codes such as E33 or E34. It is compatible with models such as 24 MFFI, 23 MFFI, and 27 BFFI, among others. A technician must confirm through diagnosis whether it is necessary to replace it when there are faults in the pressure or it prevents the boiler from igniting.
- Type of part
- Pressure switches
- Status
- Refurbished
- Catalogue reference
- 998484-01
- Warranty
- 1 year
Ariston boilers compatible with reference 998484-01
Pressure switch with reference 998484-01. Eight confirmed compatibilities: 24 MFFI and 23 MFFI.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Ariston 24 MFFI | City | Contrasted |
| Ariston 23 MFFI | EST | Contrasted |
| Ariston 27 BFFI | Genus | Contrasted |
| Ariston 23 MFFI | Microcombi | Contrasted |
| Ariston 23 MFFI | Microgenus | Contrasted |
| Ariston 23 MFFI | Microtec | Contrasted |
| Ariston 23 MFFI | T2 | Contrasted |
| Ariston 24 MFFI | ONE | Contrasted |
Can't see your model or have questions? The printed reference takes precedence. How to check it · Send us a photo via WhatsApp.
How to check if ref. 998484-01 is the part for your boiler
The part reference, model, and equipment revision must be verified against the manufacturer's documentation.
- Find the reference printed on the installed part and check whether it matches the catalogue reference 998484-01. If it is not visible, do not identify the part from its shape alone.
- Check the full boiler model on its data plate and look for it in the model associations on this page.
- Compare the connections and physical body with the original part before installation.
- If anything is unclear, send us a photo of the marking via WhatsApp before placing your order.
Symptoms that require diagnosis in the pressure switch 998484-01
The pressure switch controls the air or water pressure to authorize operation. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The extractor works and sounds fine, but the boiler does not ignite the burner.
Cause: The pressure switch does not indicate to the control board that there is sufficient pressure in the air circuit, so the gas does not open.
Check that the connection tube from the pressure switch to the fan is not disconnected, crushed, or has condensation inside.
- 02
The display shows an air pressure switch warning that sometimes disappears after resetting.
Cause: An intermittent fault is usually caused by a contact that degrades before fully opening.
Reset and note if the fault takes longer or shorter to reoccur; if it is more frequent, the part is failing.
- 03
The boiler fails more when starting cold in the morning than during the rest of the day.
Cause: The pressure switch is sensitive to small variations, and dirt or cold can cause it to fail only during startup.
Carefully clean the area around the pressure inlet and check for any dust or soot buildup before replacing the part.
- 04
The extractor is spinning but it seems to be struggling, and just then the pressure switch fault occurs.
Cause: If the extractor loses power, the pressure switch stops receiving the minimum pressure even if it is in good condition.
Check the condition of the extractor (noise, vibration, speed) before assuming that the pressure switch is the culprit.
Ariston fault codes that require diagnosis
| Code | Fault | Technical checks |
|---|---|---|
| E33 | The air pressure switch is closed before the ignition sequence. | The pressure switch remains closed at rest (membrane stuck or wiring/connections reversed). Check with a multimeter that it is open at rest and inspect/clean the connections and pressure tubes. |
| E34 | The air pressure switch does not close when the fan operates. | The pressure switch does not change state when the fan starts (contacts open due to internal fault or insufficient ΔP). Check continuity during start-up and measure depression with a differential manometer; inspect pressure tubes/connections. |
| 607 | Authorization of the flue pressure switch preceding the ignition sequence. | The pressure switch appears 'ON' when it shouldn't (contacts stuck or connections improperly made). Verify that it is open at rest and that the connections do not create undue depression. |
| 608 | No authorization from the flue gas pressure switch with the fan on. | The pressure switch does not close despite the fan turning (defective diaphragm/switch or insufficient ΔP). Check continuity when starting and measure ΔP; inspect tubes and chimney obstructions. |
| 6P1 | Delay in air pressure switch authorization. | The pressure switch takes time to close due to being sluggish or due to limit depression. Check the closing time with a multimeter and measure ΔP during pre-ventilation; clean/adjust connections. |
| 6P2 | Air pressure switch opening during operation. | The pressure switch opens during operation (unstable contact or draft/pressure drop). Check continuity in operation and measure sustained ΔP; inspect tubes, obstructions, and the pressure switch itself. |
These symptoms can have more than one cause. If your boiler displays a fault code, send it to us via WhatsApp along with a photo of the labeling, and we'll tell you if this is the part.
Datasheet for Ariston Pressure Switch 998484-01
- Catalogue reference
- 998484-01
- Uniclima internal SKU
- PHT223MFFI
- Brand
- Ariston
- Type of part
- Pressure switches
- Units in stock
- 3 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- Delivery time shown at checkout
- Return
- 14 days
Part data and available documentation
Contrast the label codes, PCB, and revision with the installed part; they are not necessarily equivalent references.
- Label code
- 605 99509
- Switching pressure
- 40/△+12 Pa
- Range
- 0.2(0.1)/30~
- Batch code
- CHKDCC
- Serial number/batch
- MTS 2399551018000
Frequently asked questions about the pressure switch 998484-01
Does the pressure switch Ref. 605 99509 work for an Ariston Genus 27 BFFI?
What fault does this pressure switch resolve in an Ariston MFFI boiler?
At what pressure does the pressure switch of the Ariston UNO 24 MFFI switch?
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