Heated towel rail not working

[shedder]

I've just installed an evohome system, and most of it is working well. Most of the radiators had Drayton TRV4s, and I've swapped them all for HR92s, and they're working fine. However, in the bathroom there's a heated towel rail which had an Iflo TRV. The compatibility page says it should work with no adapter needed, but it doesn't seem to be opening the valve. It's correctly bound to the controller, the signal strength is 5, and the controller seems to be accurately reporting the bathroom temperature, but the radiator never seems to come on. Can anyone suggest anything else I could try?

[Giainc]

Heated towel rails aren't necessarily directly linked to e.g. Central heating. We have towel rails that I think are linked to a separate pump that pumps water around to get hot water closer to our bathroom taps which are a long way from the boiler and hot water tank. It operates on a different schedule from the water and heating controller

[shedder]

That's not it - this one is on the main heating circuit. If I swap the HR92 for the Iflo it comes on.

[Richard]

Have you measured the valve pin height as per the video on the compatibility page?