CH.
If you have the Atmos running (CH Mode) with an external sensor I assume
from reading the blurb that the boiler alters the water supply temp by
modulating the boiler according to external air temp variation. The max,
min. and slope of the curve can also be modified I believe.

If the boiler is connected to an open therm Danfoss TP5000 which has a
Proportional and Integral function which presumably derives its control from
an internal air temp sensor, what does this actually control on the boiler?
is an on / off signal ( varying the mark to space ratio) to fire the boiler
or is there some other mysterious control function which I have missed here.
I am familiar with PID temp controllers and their action but always
controlling electrical heaters in controlled environment cabinets/ rooms, in
this situation the mark to space ratio can be a matter of seconds.

It's not a good idea to switch boilers off and on repeatedly so I'm assuming
that in this case it's a compromise between minimising repeated switching
and accuracy of temperature control.

I would be grateful if anyone can confirm the above ramblings or enlighten
me on the subject.
Regards
Don