tech.aircon@samsung.com may be able to help. My immersion heater is connected only to the solar iboost, so cannot help you much. Prior to the iboost being fitted, my memory of the disinfection cycle was that it only used the immersion heater and the outside unit was not involved. 

@mike-h Thank you. I'm interested in your experience with the iboost. It's something we've considered. How do you use it? Does it work well for you? Is it controlled via the Samsung controller or separately?

@bauchie I like the iboost. It’s pretty simple and it does our hot water for 7-8 months of the year. It operates independently of the heat pump and is directly connected to the immersion. The original connection between the Samsung wiring and the immersion was removed. It uses excess solar produced electricity, but you can also use it to run straight from the grid manually or according to a schedule.

We are on the feed-in tariff so the solar boost saves us money. Those who are getting an export tariff of 15p/kWh prefer to use the heat pump to heat DHW. 

@mike-h ah yes. That makes sense. If you get the FIT then I guess you might as well maximise your own usage! For us - we are on the newer export tariff so I guess exporting and suing the ASHP to heat our water all year round is probably cheaper as well as more efficient...

@mike-h Ive just happened upon this thread mike. You do know that you can still export to the grid at 15p per unit and keep your FIT generation tariff. You just need to apply to octopus to split them. Generation goes to FIT tariff and export goes to export tariff instead of the paltry FIT export rate. Ive done it myself and thats why my Eddi is sitting unused 🙂

@bontwoody Thanks very much for pointing this out as I was unaware that you could do this. The need for a hot water cylinder is the one thing I feel is a disadvantage of owning a heat pump. Mine is supposed to lose 0.3C per hour, but seems to lose twice that and a lot more when the Samsung does its 5 minute run every 24 hours to keep things from seizing up during the non heating season. I also don't get a particularly good COP, 1.5-2.0, when heating DHW. Leaving the iBoost to do its thing during the summer has kept things very simple, but I will certainly look into what you have suggested. Thanks again.

@mike-h No problem Mike. Actually I dont use my heat pump to heat my DHW. Im on Intelligent Octopus Go and have a Mixergy cylinder so just use the immersion at night for 7p a unit. That gives me a financial COP of about 3.5 even discounting that there might be some efficiency gains through the stratification of the Mixergy tank.

The 1.5-2 COP doesnt sound very good, there is a lot of discussion about how to get good DHW COPs on heatgeek. Big coils help but I think they are emphasing slow heating cycles too. might be worth a look.