Question regarding boiler and TRV consumption

No

Anyway, that is not how you use trvs. Warm your house up to the temperature on the thermostat you want & then go to each room & if you feel hot in it or think you can live with a lower temperature in that room then turn the tvr down until you get to the temperature you want in that room. It could mean you could turn an upstairs radiator completely off because the heat rises from downstairs.

Each radiator should have its own setting. If you are setting them all at the same level then you are throwing money down the drain whichever way you look at it.

It is all about the boiler having to heat as little radiator water as possible but still keep you comfy &/or adjust the right temperature to each room. After you have done it then shutting all the doors will help further because you can adjust trvs lower in the warmest rooms like the lounge, which is normally the room you want the most heat in & ideally you don't want it just floating upstairs. (edited)

Unless the trv is able to control the boiler then isn’t what you set the trv to a bit of a moot point or have I not understood the question?

The only thing that might help lower the costs in a dumb trv environment is if the rooms all get to temp and they close their valves which would mean that the boiler will most probably not have to keep firing to keep the circulating water hot but even that would depend on the boiler?

Thanks all for sharing best practices around TRV use.

But my question remains unanswered.

Is the cost the same as having trv set to full compared to 2.5?