A C in the top-right corner should be visible indicating TX module and Receiver are connected and Communicating. However you say "Turned the thermostat right down but heating stayed on." which does not seem to point to the programmer. With the release of ExpressLRS v3.0, updating your Binding Phrase via the WebUI is an even more compelling reason to use a Binding Phrase. a TX Module with version string of 3.2.0 will NOT sync or bind with a Receiver with firmware version 2.4.0 Records the default button state of the corresponding category & the status of CCPA. It works only in coordination with the primary cookie.

A Receiver flashed or set with a Binding Phrase WILL NOT initiate Manual Binding mode, however many times you try the procedure below. You must first reflash the receiver with the Binding Phrase field disabled and/or unset. Why would you not use a bind phrase though if you're already having to flash the RX anyway? There is a 230 volt and 24 volt model it seems, this is the instructions. https://www.plumbase.co.uk/link/1/h002877_20563_t.pdf You are now in the Tools Menu where Lua Scripts can be found. Scroll down and select ExpressLRS Lua Script.SPI-based Receivers on Betaflight 4.4.0 and newer will only sync or bind with ExpressLRS 3.x firmware Power up your transmitter/radio and use the [BIND] button on the ExpressLRS Lua script, which sends out a binding pulse. The Popup will briefly show up and then disappear.

a Receiver with version string of 3.1.2 will sync and work with a TX Module with firmware version 3.0.1 If the button is being pressed or pinched, remove the cause of the pressing or pinching. Heatshrink can sometimes press a button on the receiver.Older Radios or those with only one Menu Key will need to long-press the Menu Key to access the System Menu. If the other UART is occupied by another peripheral, disconnect it and swap places with the Receiver. Disconnect the RX and TX wires of the Receiver from the Flight Controller. Reconnect power to the drone or aircraft. Observe the LED on the Receiver once again.