Mounting radiator thermostat on M28x1.5 thread

Hello, and apologies in advance for my poor terminology. I am quite a novice when it comes to plumbing and heating.

I am planning a bathroom renovation and am going to install underfloor heating. I am going to use a product that is potentially only marketed in Sweden/the Nordics, called LK minikretsventil M5. It has what I believe to be a standard M28x1.5 connection/thread, or whatever it is called. I have 13 tado° thermostats already, so I am loath to invest in some other separate system... would be nice to have all rooms controlled through one app.

Included with the smart radiator thermostat, there is an adapter that does fit both sides (and on it, it says M28x1.5-00 on one side): the end with the pointy hexagonal thing fits perfectly on the tado° end, and the end with the two screws fits perfectly on the brass piece to the left in the photo.

My problem now is that the little metal pin is way too short: when all the things in the picture are assembled, the pin does not protrude through the hole and so cannot be reached by the actuator on the tado° end. When manually holding the thermostat down firmly, I can see that it can push the pin seemingly through the whole range of motion. My only problem is that the pin is too short or, conversely, that the adapter is too long...

What would be the best solution here? I am thinking either (1) an "extender pin", which can be a rigid piece of metal 3–4 mm in diameter and 30ish mm long, or, for a maybe more solid solution, (2) a "thread shrinkerer" (yeah, this is where my lack of terminology is evident) with an inside thread matching M28x1.5 and an outside matching tado°'s, whatever that is.

Ideas, comments, suggestions?


  • Maybe it’s trickier than I thought.
  • Hi,

    You might want to check that this is not an RTL (Return Temperature Limiter) valve, which requires a thermostat that feels the flow temperature over the valve pin. This is often used for bathroom radiators and underfloor heating, and is not compatible with our Smart Radiator Thermostats.

    If in doubt, contact our support with pictures of the original thermostat:

    Best regards,


  • Hi, Frank!

    I think I’ve solved it, thank you. One of the pins included (but forgotten by me) solves this. The device does have a return temperature limiter, but that is separate to the valve that the thermostat/actuator manoeuvres.

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