TX3 to Sika VVX20 Flow Meter

You didn’t mention that before!
Yes, I think you may well find a pulse there, but the comment about pin use might mean it’s custom software and it’s not included.

If that’s the case, if you’re careful then monitoring the voltage output will probably still work, but you must make sure that everything you use to do that is isolated from everything else except the heat exchanger - i.e. you use an isolated mains supply to your Arduino and opto-coupler or radio to get the data out.

Thank you. I have setup a Arduino to read a handful of DS18B20 thermometers and issue the data via MQTT. I aim to get this setup over the next few weeks.

Happy to share the code if anyone wants it.

I am then going to get a oscilloscope and test the output of the flowmeter. I suspect that I will find an unused pulse, which I can connect via an optical coupler to a second Arduino.

@gck303 - George, did you connect your VVX20 Mitsi to your EmonTx3 in the end? I have an identical (Ecodan) pair of pumps, and am trying to connect to an EmonTx via the digital output . Any insights follwing on from your Jan post would be really helpful.

I guess plan B would be to assemble the dedicated board, which is where your post started off…


The same (or very similar) flow meter is also included as standard with Samsung heat pumps, although the part number looks like it’s Samsung specific.

@gck303 did you have any luck testing the pulse output?

I’m installing a Samsung heatpump soon, so I’ll try and test.

To intercept the signal from the flow sensor while the sensor is plugged into the ASHP controller we need to make a mini PCB adaptor. This is the plug that my Samsung branded VVX sensor came with, can anyone identify what plug this is and what connector will be required to plug into it?

@gck303 can you confirm if your Mitsubishi branded VVX has the same connector?

It’s a silly question - is there nothing anywhere on the moulding? Knowing the pin spacing and physical dimensions might allow you to narrow the choice down. It almost looks automotive.

The headers on the PCB look similar - is there any marking on those?

There are no markings on the connector.

The dimensions are 10mm x 5mm and the pitch is 3mm

Sorry, I don’t think I can put a name to that. I have a feeling I’ve seen one, but that’s about all.

Have you tried uploading an image of it to Google Lens?

The closest I could find were these ‘JST’ type connectors from TE Connectivity:


But that’s 3.98 mm (call it 4) pitch, a 4-pin is 15 mm long, not 10.

It might still be worth sending the pictures to Mouser or TE with a “Can you identify this?” plea.

I think I’ve found the connector:

But the RS product listing doesn’t give any info as to compatible resereceptacles. I think it could be Smw250, but these look hard to get hold of:

It looks like the same part is used for Samsung A/C sensors:

There’s an obvious reason why you didn’t find it earlier: from the data sheet…

Connection Gender Male
Connector Type A Circular Plug


It’s probably worth an email to RS asking for details of the mating connector.

Ok apparently the part number for the connectors are:

Socket: A2502-WV04
Plug: A2502-H04

Here’s the datasheet:
1811140021_BOOMELE-Boom-Precision-Elec-XHB-2A_C57981.pdf (2.9 MB)

These parts seem to only be available from one supplier in China, I’ve ordered a sample MOQ of 50 PCS. Let me know if anyone wants some for testing?

The eventual plan is to make a little breakout PCB to sit inline between the sensor and the HP controller to intercept the signal from the Sika. It seems this exact same sensor is used in Samsung, Mitsubishi and Vaillant ASHP units, being able to read the flow rate from this sensor will enable us to monitor COP for these units without having to fit an expensive heat meter.


Connectors have arrived, and I’m in the process of making up a breakout PCB.

@gck303 can you confirm if your Mitsubishi branded Sika has the same connector and wire colours as my Samsung branded version?

Here’s the pinout of the Samsung sensor, it’s yet to be determined if the Mitsubishi sensor uses the same connector and pinout, is anyone able to check?

  • pin 1 5V | Black
  • pin2: flow | White
  • pin3: GND | Blue
  • pin3: pulse | Brown

I have an Ecodan that I am currently looking to add some monitoring to as I don’t have a level 3 RHI package, and getting the flow rate without the disruption of adding a meter would be very useful. The board on my FT6 looks to be using the JST type plug referenced by Gwil in the post above and the wires are coloured in the same order.

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Ecodan’s use a different plug to Samsung. However, the good news is the same connections are broken out on the screw terminals below which makes reading from the Sika sensor much easier.

Here are the terminals

@TrystanLea could you share the pinout for these

Hi, I’m new to the forum and have found the above thread useful so far in trying to extract the signal from an identical Samsung sensor. Did you have success reading a (digital/analogue?) signal through the breakout PCB?

Yes, it’s possible to connect the Sika flow meter to an emontx V4 running heatpump monitor firmware which will read the flow rate, this is documented here: https://docs.openenergymonitor.org/emontx4/heatpumpmonitor.html#reading-from-a-sika-vfs-analog-output