Vaillant ecoCOMPACT VSC IT 2462-C 170 DHW Management via External Relay

Hallo members,
I would like to manage the Domestic Hot Water Production (DHW) of a Vaillant combined boiler ecoCOMPACT VSC IT 246/2-C 170 by an external relé.
The system is equipped with the additional unit calorMATIC VRC 430 and the external temperature sensor. In any case, I'm not currently interested in using the calorMATIC device because I have a random use of DHW, so the weekly program function does not fit my needs as well as the possibility to maintain hot water at a set temperature value continuously.
The Central Heating system (CH) is managed by relé using the RT 230 V - AC connector (violet and orange conductors in the attached picture) and I would be great to do the same for DHW, setting a fixed value of the hot water by knob and managing the ON/OFF DHW production without the use of eBUS.

I have also attached some pictures for a more clear idea of the current configuration and reference wiring diagram.
Thanks a lot for any advice.

One way is to switch between the DHW sensor and a resistor to simulate a high temperature on the tank. A remote control relay can be used for this.

>>21269650 >>21269650 Hi Damian, thanks a lot for your quick reply, that is a smart solution. I made some tests on the DHW sensor (part number 253552) in order to evaluate the resistance offered at different temperatures. As I understood, such sensor is NTC type (Negative Temperature Coefficient) and the resistance value ranges from 1.35 kohm at 40 °C to 0.9 kohm at 60° approximately. So I think that a 0.8 kohm would be okay to avoid the start of DHW production and short circuit error (F.13). Let me get a proper resistor and I'll let you know. I also was thinking that, since the boiler installed has 100 liters capacity, it would be useful to partially load such item instead of heating the full water amount. Do you have an idea about how to do such energy optimization? Thank you!

Looking at the tables from the NTC10K sensor at 0.9 kOhm will read around 98 degrees.
As for the second part, please describe what you would like to achieve. If it is convenient for you it can also be in English.

>>21272850 Unfortunately I don't have any document of the sensor and values have been derived by setting the DHW temperature with the on-board knob and measuring the resistance once the burner has stopped. Your information is surely more reliable than mine. So, since the maximum temperature that can be set by knob is 60 °C and, according to the manual, the safety limit has set at 130 °C (error F.13), the 0.9 kOhm should be satisfying. Regarding the second topic and based on my basic understanding of the operating condition, anytime there is a request of DHW the system starts to prepare 100 l (tank capacity) of hot water at the preset temperature value, for convenience we assume 60 °C (Am I right?). Sometimes there is no need of 100 l of DHW at 60 °C, but 60 l at 60 °C would be enough. So, my question is: Is there a possibility to heat a lower amount of domestic water than the full tank capacity at the preset temperature value? Thanks for the support. P.S.: regarding the language, the forum automatic translation is working fine so far, so go ahead as you wish.

It is not possible to heat less water. The water at rest will want to equalise its temperature later anyway. Of course there will be some stratification warmer water at the top and colder water at the bottom.
Try still disconnecting the DHW temperature sensor cube. In wall-hung boilers working with a separate DHW tank, disconnecting the cube disables the DHW heating function - the boiler thinks there is no tank at all. Connecting the sensor immediately activates the DHW temperature monitoring function. I don't know how in this COMPACT boiler?

>>21274361 Thanks for your reply firstly.
The disconnection of the DHW temperature sensor causes the error F.3 (sensor interruption) and no DHW is produced.
Do you think that some action on the loading pump highlighted in the attached picture would be useful for the purpose?
Thank you.

Hi guys,
I finally had some time to spend for the implementation of the @damian5602 solution by using:
- an additional resistor, to simulate a high temperature of water when hot water is not necessary, into a circuit branch under a normally closed (NC) switch;
- the original thermistor, to read the effective water temperature when hot water is needed, into a circuit branch under a normally opened (NO) switch;
- a smart switch (Shelly Pro 4 PM) as controller of the NA/NC switch;

The system is working fine even considering all the benefits derived from using a smart switch having too many connecting and configuration options.

Thanks a lot to @damian5602 and @ls_77 for inspiring.