ref: boss therm model bps242rf?

We have had the above installed in a new property for 15 norths now and have never had the controller operating automatically in all that time. I have set the send and receiver done the learn sequence etc and it all connects standing next to the boiler(receiver) with the sender - which are in the garage. I then take the sender indoors and mount it on the wall.
All is fine until the room reaches temperature and shuts the boiler off. From then on I cannot get the sender and receiver to communicate, unless I take the sender to the receiver set the required temp. and the boiler starts again.

It programmable BPS242RF appears not fit for purpose. I am now contemplating replacing the system entirely.

Can you submit any practical advice?