We disable/turn off all the thermostats that call for heat - this means the buffer doesn't heat for the central heating. Our ASHP remains "on" but the only thing it does is HW. 

Correct me if I'm wrong, but is heatmiser an on/off thermostat type controller?

Can you describe your GSHP a bit more:

Make / model /power?  Is it inverting, or on/off (small ones usually are)?

My knowledge is all generic I'm afraid - I made my own gshp, it has no buffer, and just feeds rads or a DHW tank on demand.  Ours is just a 2.5kW on/off unit, as many small gshp are.

As to whether you can turn off the buffer, but keep DHW depends on how it is plumbed and controlled.  Do you have a conventional DHW tank as well as the buffer?  Here's a simplified pic of ours (replace boiler with gshp)- could you find/draw a picture of yours, I think it would help a lot:

Posted by: @square93

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I have a new GSHP system, installed in January 2023.  It is a all-new retrofit but that’s just for background.  I have gradually fine-tuned to our needs and it is working well. 
The controller is CTC Ecologic.

What should I do during the summer.  I normally don’t need heat from May to end Sept (or can use secondary source for minor cold spells).

I have the room thermostat (Heatmiser) down low and that is stopping the heat but (correct me if I’m wrong) the system is still keeping the Buffer tank hot.  I still want DHW all summer but surely Its costing me money to keep the buffer hot for several months.

Is there a way to switch off Heating and Buffer but retaining DHW or am I over-concerned.  Is best practice to turn system down but leave it running?

 

Does the CTC controller or an in-built display on the heat pump unit allow you to program when the heating is on or off?

You may also find it beneficial to control the hot water settings too. My hot water is set to only turn on for an hour in the morning and a couple of hours in the evening, although I expect the saving from this is minimal. 

@robl We have the Heatmiser Neo Air V2 and this is an on/off system. Can’t locate the setting right now but, I’m certain there is an adjustment for hysteresis but that is all. I had hoped to have a Homely Smart Controller but, as yet, there isn’t a version for the Daikin that will control 2 separate pumps. Regards, Toodles.