Pretty sure it’s reverse circulation, hot water was running there and I could feel the return to the rads hot. It’s connected to the return from the coil on the cylinder. Not sure why it would have been done that way. Three way valve etc is in the attic above the hotpress so I assume they could have just continued the old radiators return up there and connected in? Even if they add a non return valve now on the rad return it still means when the rad circuit is on its pumping through the cylinder coil? Which probably doesn’t make much difference.. it’s funny my family were complaining the house was way to warm and blaming the heatpump.. I was explaining all it as doing was heating water last month but it’s also putting some heat back into the rads during the hot water cycles probably 1.5 times a day. Probably not helping the efficiency of the hot water cycle either
Mine does exactly the same. After the hot water cycle the valve moves back to the default CH position and a small amound of warmth can be felt on the top of the radiators in our loft conversion. I don’t think it would be enough to actually warm anything up in my case, but I would prefer it not to do it. When the installer comes out to service it in a couple of months I’ll mention it to him
It’s definitely reverse circulation on ours. Hot water is going into the return from the cylinder coil into the rad return.. they probably shouldn’t have plumbed it this way. Installer is going to come back to fit a non return valve on the return to rads..
After my DHW cycle i can feel a big chunk of hot water go round the pipes, makes them click a lot with expansion. I’ve never really felt the rads but would imagine it wouldn’t heat them up much but you can absolutely feel it in the pipes. Goes hot then cool.