Samsung 12kW Gen 6 ASHP struggling to heat DHW. Advice needed please.

[MikeJH]

Hi, my 12kW Gen 6 ASHP normally will heat my domestic hot water from 20 deg C to 53 deg C in about 30 minutes and uses around 1.5kWh. Recently, it has been intermittently struggling to do so with the compressor stopping twice during the process and using much more energy. The two figures from PassivLiving illustrate the change in behaviour. On 8th November, the flow temperature rises steadily to 63 deg C. The energy output which is recorded over 2 minute intervals runs at around 0.265 kWh (ie power of nearly 8kW). By contrast, on 9th November, the flow temperature rises more slowly and the energy output after a brief peak drops to the same level as consumption. Both then drop to zero as the compressor stops for a short period. By the end of the process consumption is greater than energy output. The flow rate is 19L/min, which is slightly lower than when space heating (22L/min). I have had no problems with space heating, so I wonder if it is something to do with the DHW cylinder which is a Telford Tempest Heat Pump 170 L tank. I would be very grateful for any advice.

[JohnMo]

Are your internal and external temperatures connected up and reading correct? Outside temp look very similar for different days.

 

Is it doing a defrost?

[MikeJH]

1 hour ago, JohnMo said:

Are your internal and external temperatures connected up and reading correct? Outside temp look very similar for different days.

 

Is it doing a defrost?

Thanks. PassivLiving gets the outside temperatures from the nearest weather station, so are close to the actual temperatures at my location, but not precise. The internal temperatures are reading correctly. It wasn't doing a defrost.