Michael Chare wrote

With a conventional programmer the boiler is trying to keep itself warm
whenever
the timer says the C/H is on which in your case would be always.

This is not true, certainly not in every case. With my Honeywell S Plan system
with conventional programmer, the power to the boiler is controlled by
microswitches in the motorised valves which only operate when the stats are
calling for heat. Only the frost stat overrides this.

IMO the question of whether to have the heating on constantly has more to do
with personal preferences and the thermal capacity of the building rather than
with efficiency. It will always be marginally more efficient in itself to turn
the heating off when not required, but if the building cools down quickly (or
warms up slowly) to the extent that you need another heat source (eg a gas fire
or fan heater) to reach the comfort zone when you come home, this instantly
wipes out any benefit of switching off the heating. Like Danny, I leave mine on
constantly at a lower temp.

Peter