Yes, with a multimeter or 2 pole voltage indicatorDo you know how we could check the heat link?
Have you checked the 'predictive heating' protocol? Ours was set in the (default) on position. It would come on at all hours.My Vailliant boiler (EcoTEC plus 937) which has a nest thermostat attached id not turning off the central heating!? We have turned off the Nest thermostat but the boiler continues to heat the radiators?