I know some makes of remote changed the frequency used, they do not say why, I would assume they use a permitted frequency in the USA or Europe which was not permitted here in the UK. So even using one from the same manufacturer may not work.
I had problems with mother's house,
I fitted two wireless systems one shown top of picture one bottom, the original shown here,
was very good, it had a loss of RF signal safety device so if no signal in ½ hour it would auto turn off boiler, so with a discharged battery it failed safe. It also had a mark/space ratio, so it would start cycling the boiler on/off as it approached the target temperature, ideal with a non modulating boiler, but not what is wanted with a modulating boiler, and it had no programming functions.
This one
seemed far better at first, it could be programmed, and also did not have the mark/space thing, so would allow the TRV to do its job, however it gradually over time lost the RF linking, and had to be placed closer and closer to the receiver to work, and had no fail-safe, so would start the boiler, then not turn it off again.
After this I decided, one did not want a battery powered unit if I could help it, and two if using RF wanted a two-way unit, basic idea is one confirms with other signal has been received.
I still got it wrong, I went with Nest Gen 3, only to find out after getting it, they had stopped supporting the linking with Energenie TRV heads, so now considering again using two thermostats in parallel, but as yet not made my mind up, Drayton Wiser, or Hive, the Drayton Wiser more expensive, but also it seems better.
The Horstmann thermostat shown it seems is sold under many names, I assume made in China and different labels used.
