on the subject of the grant vortex combi actually – It lives outside and is fairly poorly insulated.
Annoyingly it heats up a small tank of water inside it for on demand water. – this it fires up every 90 minutes for 3 minutes to maintain that tank temp – and the maths works out that it accounts for why my oil usage for hot water over the summer is so much when the heatings been off.(always has consumed this much over summer its not a new thing)
till now I’ve had a controller with no timer on the hot water- I’m toying with wiring up the second channel on the thermostat to switch of the hot water side during the night and assuming the smart thermostat can do it – when we are away and letting the frost stat control the firing.
Next year once the solar thermals in the combi water heating will likely get wired off permanently when i move the heating controls onto the tank valves.