When it is cold and my 12 kW Samsung Gen 6 ASHP is not running, the water pump periodically runs for 5 minutes to keep the circuit from freezing and takes heat from the DHW circuit. This is standard behaviour and apart from reducing the temperature of our DHW, it usually doesn’t cause any problems. However, I have noticed that if the space heating is scheduled to come on during one of these freeze prevention episodes, then the space heating behaves very abnormally as in the graphic below.
The compressor starts while the 3 way valve is still switched to the DHW circuit making it appear on the Emoncms graphic as if it is heating DHW. The valve then switches to space heating, but electricity consumption rises to very high levels with an instantaneous COP falling to 1.1. The first time this happened, the compressor stopped by itself and then restarted a few minutes later and space heating returned to normal. On this occasion, I stopped it and restarted it.
Has anyone seen this behaviour before and has anyone any suggestions how I might avoid future occurrences?