[spudstrawb]

Thanks Allan. As you say, it definitely has SHT21 and HTU21 markings. I tried once again setting it to SHT21 but the same thing happened. I got the first 2 flashes from TX led, then nothing.

The board is TX v3.1.2 and the software is TX_v2.0_b009.

This has all been a good experience for me. I'd not done anything with Arduino stuff before, so I've learnt a bit there. It was a bit confronting at first but it's quite simple once you've done it a couple of times.

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This might be the problem... I found this quote from Werk_AG in another thread:
"The question is, the SHT2x series communicates using the I2C protocol, which implies that you also have to install the I2C bus extender Philips chip on the TX unit, which is not required for the SHT1X series."

I haven't installed an I2C bus extender. I'll either get hold of one or else get an SHT1X sensor.

I have another problem now. My WD unit is locking up. Once it gets the values from the RX unit, either the screen goes white or it locks up (the 2 dots stop blinking).

Hopefully there aren't too many more issues to overcome.