Hydraulic Block Saunier Duval Isofast Condens F 35 E
If you notice leaks, pressure loss, or problems with hot water production, you may need the hydraulic block Saunier Duval Isofast Condens F 35 E. This part is a hydraulic component responsible for directing and distributing water between the circuits of the boiler. When it fails, it can trigger fault codes such as F.75, F.23, F.24, or F.20. It is compatible with several models, including Isofast Condens F 35 E, Isofast Condens F 30 E, and Themafast Condens F 30E, among others. It is recommended to replace it upon detecting the mentioned symptoms.
VAT included
Consult via WhatsAppSaunier Duval boilers compatible with reference 0020037988
Hydraulic group with reference 0020037988. 12 verified compatibilities: Isofast Condens F 35 E and Isofast Condens F 30 E.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Isofast Condens F 35 E | Isofast Condens | Contrasted |
| Saunier Duval Isofast Condens F 30 E | Isofast Condens | Contrasted |
| Saunier Duval Isofast 21 Condens F 35-B | Isofast Condens | Contrasted |
| Saunier Duval Isofast 21 Condens F 25 | Isofast Condens | Contrasted |
| Saunier Duval Isofast F 30 E H-MOD | Isofast (non-condensing) | Contrasted |
| Saunier Duval Isofast F 35 EA | Isofast (non-condensing) | Contrasted |
| Saunier Duval Isofast F35E H-MOD | Isofast (non-condensing) | Contrasted |
| Saunier Duval Themafast Condens F 24E | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 30E | Themafast Condens | Contrasted |
| Saunier Duval Themafast Condens F 30 H-MOD | Themafast Condens | Contrasted |
| Saunier Duval Themafast F 30 E H-MOD | Themafast | Contrasted |
| Saunier Duval Themafast F 25 E H-MOD | Themafast | 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. 0020037988 is the part for your boiler
What determines it is not the boiler model, but the reference printed on the part you already have installed.
- Find the reference printed on the installed part and check whether it matches the catalogue reference 0020037988. 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 and faults that the hydraulic group 0020037988 resolves.
The hydraulic group includes the valve, the by-pass, and the water connections. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
The domestic hot water comes out lukewarm or takes a long time to heat up when the tap is turned on.
Cause: The hydraulic block does not distribute water properly to the domestic hot water circuit due to an obstruction or internal wear.
Open the tap fully and measure the actual flow rate, ensuring that there is no issue with the mains pressure, before replacing the block.
- 02
A clicking sound is heard every time the boiler switches from heating to domestic hot water or vice versa.
Cause: The diverter valve of the block does not change position correctly and either hits or gets stuck halfway due to wear.
Note that the noise always occurs right when opening or closing a tap, not continuously, before considering the gas valve faulty.
- 03
Do the radiators heat up when only hot water is requested, or vice versa?
Cause: The diverter valve of the block does not close one of the paths properly and mixes the heating and domestic hot water circuits.
Request only domestic hot water (DHW) and touch the radiators by hand to check if they also heat up, confirming that it is not an issue with external valves.
- 04
Moisture or a small leak appears in the lower area of the boiler without a clear source.
Cause: The hydraulic block can develop cracks due to heat cycles or accumulate limescale in its internal joints.
Dry the area, leave the boiler off for a few hours, and check if the moisture reappears right under the block before replacing it.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F.75 | The control does not detect an increase in pressure when the pump starts (lack of water/pressure or pump/sensor fault). | If the circulator (block 0020037988) is blocked, does not start, or does not respond, the pressure sensor does not detect the expected increase and the boiler locks out with F.75; check electrical/PWM start-up, consumption, and that the rotor spins after bleeding. |
| F.23 | Safety shutdown due to excessive temperature difference between flow and return. | A blocked pump or one working at minimum power prevents circulation, increases the ΔT, and triggers F.23; check that the circulator is rotating, its consumption and flow rate, and bleed the primary. |
| F.24 | Safety shutdown due to excessively rapid temperature rise. | If the circulator of block 0020037988 is seized or has insufficient power, the water does not dissipate heat and the temperature rises quickly; check the pump's rotation/consumption, PWM signal, and bleed the circuit. |
| F.20 | Safety shutdown of the temperature limiter (overheating). | The lack of circulation due to a blocked pump in block 0020037988 causes overheating in the heat exchanger; check the start and flow of the circulator, free the shaft if it is seized, and bleed. |
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.
Data sheet for the Saunier Duval hydraulic group 0020037988
- Catalogue reference
- 0020037988
- Brand
- Saunier Duval
- Type of part
- Hydraulic units
- Units in stock
- 5 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- 1-2 business days
- Return
- 14 days
Manuals and technical documentation
Official documentation of the boiler, useful for locating the part and cross-referencing the fault codes.
- Saunier Duval Isofast 21 Condens F 35-B Manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the hydraulic group 0020037988
Is this hydraulic block compatible with several Saunier Duval boilers?
For which specific models is the hydraulic block HBICF35E compatible?
Can the hydraulic block HBICF35E solve faults in the boiler?
Does this hydraulic block work for the Themafast F 30 E boiler?
How many models are compatible with the hydraulic block HBICF35E?
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