For some time now, my thermostat has been flashing the word "Service" above the temperature. Does the boiler want servicing, or the thermostat? Also, the thermostat is programmed to switch the boiler off at 9pm, but it no longer does so. Nor does the thermostat allow me to re-programme. It does not need new batteries. Do I need a new thermostat, an electrician, or a plumber? Please help.