I had a new boiler installed 3 years ago, along with a Salus ST620WBC thermostat and control unit. The thermostat batteries went and were replaced but then it stopped working a few months after and would not work with new batteries as the display just kept flickering. I rang the manufacturer and they advised it was faulty and would need replacing and that this particular thermostat was discontinued. I thought I had sourced the same one online but it won't pair with the existing control unit. The new one came with a new control unit so it seems that I will have to get this fitted also, and by a gas safe Engineer? It will involve taking the cover off so I don't think I can do this myself? without voiding the warranty for the boiler anyway.