3-Way Valve Saunier Duval 3 Isotwin F28 EA Ref. 05720800
The Saunier Duval 3-way valve 3 Isotwin F28 EA Ref. 05720800 controls the flow of water between the heating circuit and the domestic hot water circuit. When it fails, you may notice that there is hot water but no heating, or vice versa, and it can even happen that both circuits mix. It is compatible with boilers from the Isofast, Isomax, and Isotwin ranges, such as the Isofast F 28 E, Isomax F 28 E, and Isotwin C 28 EA models, among others. It is recommended to replace the valve when you detect the faults F.318 or F.326, which indicate problems in its operation.
Saunier Duval boilers compatible with reference 05720800
3-way valve with reference 05720800. 17 verified compatibilities: Isofast C 28 E and Isofast C 28 E1.
Proven compatibility
| Boiler model | Family | Verification |
|---|---|---|
| Saunier Duval Isofast C 28 E | Isofast | Contrasted |
| Saunier Duval Isofast C 28 E1 | Isofast | Contrasted |
| Saunier Duval Isofast C 35 E | Isofast | Contrasted |
| Saunier Duval Isofast C 35 E1 | Isofast | Contrasted |
| Saunier Duval Isofast F 28 E | Isofast | Contrasted |
| Saunier Duval Isofast F 28 E1 | Isofast | Contrasted |
| Saunier Duval Isofast F 35 E | Isofast | Contrasted |
| Saunier Duval Isofast F 35 E1 | Isofast | Contrasted |
| Saunier Duval Isomax C 28 E | Isomax | Contrasted |
| Saunier Duval Isomax C 28 E2 | Isomax | Contrasted |
| Saunier Duval Isomax F 28 E | Isomax | Contrasted |
| Saunier Duval Isomax F 28 E2 | Isomax | Contrasted |
| Saunier Duval Isotwin C 24 EA | Isotwin | Contrasted |
| Saunier Duval Isotwin C 28 EA | Isotwin | Contrasted |
| Saunier Duval Isotwin F 24 E | Isotwin | Contrasted |
| Saunier Duval Isotwin F 24 EA | Isotwin | Contrasted |
| Saunier Duval Isotwin F 28 EA | Isotwin | 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. 05720800 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 05720800. 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 3-way valve 05720800 resolves.
The 3-way valve diverts water between heating and domestic hot water. These are the typical symptoms and what to do:
Common symptoms and faults
- 01
There is no domestic hot water while the heating works normally, or vice versa.
Cause: The valve motor cannot move the shutter to the opposite circuit, so the water keeps flowing in the same direction.
With the boiler requesting domestic hot water, check if the pipe to that circuit heats up; if it doesn't change temperature, the valve is not switching.
- 02
The boiler heats radiators and the hot water tap simultaneously, without distinguishing circuits.
Cause: The shutter has become stuck halfway and allows partial flow to both circuits instead of closing one.
Check that the actuator completes its travel with a clear stop when starting the boiler; if it stops halfway, the problem is mechanical rather than electrical.
- 03
Lukewarm or irregular temperature water when opening a hot water tap.
Cause: The valve does not fully close the flow to heating, and part of the flow mixes between the two circuits.
Close the radiator valves for a moment and see if the tap temperature stabilizes; if it improves, the valve closure is suspect.
- 04
The valve takes several seconds to switch and a prolonged buzzing sound from the motor can be heard.
Cause: The internal gear motor loses power with wear and has difficulty moving the shutter.
Time how long it takes to switch from domestic hot water to heating; more than 10-15 seconds with a sustained buzzing indicates a fatigued motor.
Fault codes from Saunier Duval that this spare part resolves.
| Code | Fault | Diagnosis and solution |
|---|---|---|
| F.318 | The 3-way motorised valve is not moving. | Motor (head) lock/fault or loose connector of the V3V; check from diagnostics the actuator test, power the motor and check wiring and mechanical path/shutter. |
| F.326 | The hydraulic test detects that at least two hydraulic components are not functioning. | Blocked/non-sealed V3V prevents test completion; check DHW/heating switching (middle position), operate the valve from service and inspect the connector and wiring harness. |
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 05720800 three-way valve.
- Catalogue reference
- 05720800
- Brand
- Saunier Duval
- Type of part
- 3-way valves
- Units in stock
- 2 units
- Status
- Refurbished
- Warranty
- 1 year
- Shipping
- Delivery time shown at checkout
- 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 Isotwin C 28 EA manual (PDF)Document © Saunier Duval, provided as a technical reference.
Frequently asked questions about the 3-way valve 05720800
Is this 3-way valve suitable for my Isotwin F28 EA boiler?
What fault does replacing this 3-way valve in an Isotwin resolve?
Spare parts related to Saunier Duval Isofast
