Saunier Duval Isofast F 35 E H-MOD Hydraulic Block
The hydraulic block Saunier Duval Isofast F 35 E H-MOD, reference 4511470, is a component that conducts and distributes water between the circuits of the boiler. When it malfunctions, leaks, pressure loss, or issues in the production of domestic hot water may be noticed. This block is compatible with different models, such as the Isofast Condens F 35 E, the Isofast F 30 E H-MOD, and the Themafast F 30 E H-MOD, among others. It is recommended to replace it upon detecting any of the fault codes F.20, F.23, F.24, or F.75, which indicate problems related to the temperature and pressure of the system.
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 heating takes a long time to warm up or the radiators remain lukewarm, even though the boiler is working.
Cause: The pump integrated into the block does not provide the necessary flow, due to a seized impeller or wear.
Before changing the part, bleed the radiators and check if the pump vibrates when starting.
- 02
There is a noticeable buzzing or strange vibration in the area of the hydraulic block with the boiler turned on.
Cause: The pump shaft is turning with resistance or is working with air in the circuit.
Bleed the air from the heating circuit and try again before replacing the block.
- 03
After the summer without using the heating, the pump does not start or remains stopped.
Cause: The rotor gets stuck due to sediment or months of inactivity.
With the boiler cold and turned off, try to unlock the pump shaft with a flat screwdriver through the front slot.
- 04
Water is dripping or there is moisture under the boiler, near the hydraulic block.
Cause: The gaskets or the block body lose tightness with the cycles of heat and pressure.
Dry the area, run a heating cycle, and locate the exact point before declaring the part faulty.
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
- Hydraulics
- Units in stock
- 5 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- 1-2 business days
- Return
- 14 days
Data read on the part and in the manufacturer's documentation
What we have not been able to verify does not appear here.
- Molded code on the part
- 4511 47_
- Additional molded brand
- ">PASS-6T00<"
- The brand '>PASS-6T00<' seems to be a tooling or manufacturing mold code, not a product reference; it should not be used to order the spare part.
Frequently asked questions about the hydraulic group 0020037988
For which models is the Saunier Duval Isofast F 35 E H-MOD hydraulic block compatible?
What fault codes can be resolved with this hydraulic block?
What does the brand 'PASS-6T00' mean on this hydraulic block?
Is this hydraulic block suitable for the Isofast F 30 E H-MOD boiler?
Can I use this hydraulic block in a Themafast boiler?
Spare parts related to Saunier Duval Isofast Condens
