pairing

I have a WB Greenstar boiler with a DT10RF Thermostat (Receiever unit on the boiler and transmitter / Thermostat normally mounted on the wall). The the batteries leaked over summer when it wasn't in use and since then it shows the wrong temperature, eg 28c when it is obviously around 16c...

My dad is slightly deaf, which he's entitled to be because he's 92. This means the TV can be on very loudly at times, which annoys my mum, and probably the neighbours too. I looked at branded bluetooth TV listener devices, but I'm reluctant to spend £300+ on a pair untested. I bought a pair of...