Three days ago I installed a Grundfos Alpha 2 pump. Initially all appeared to be well and the system starts up and runs well for 2 hours in the morning. However if we turn the heating on around 2pm then by about 6pm the heating system has stopped and the pump shows “ - - “ on the LCD display. Increasing the thermostat set point will not restart the pump and the only way to get everything going again is to power the whole system down for several seconds and restart it. The pump then appears to run OK for a while but then goes back to the “ - - “ display. The pump is running in the Auto mode and usually displays around 20+ watts when running. Any ideas please?