How to fix my towerstat RSD thermostat?

Hello
My radiators were not getting very hot so I looked at my thermostat and noticed that is wasn't working - batteries ran out - I changed the batteries and then noticed temp was set at 20 so I increased to 25. Then over the next couple of hours my radiators switched off completely. Boiler still working and still getting hot water but can't get radiators to come back on