Atmos HE32 & Danfoss TP5000 PI Temp controller. ??

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

I'm not familiar with this boiler, but your description sounds about right.

So, whenever the boiler is running, the burner is modulated in order to produce a water temperature which is a function of the outside temperature - but the boiler only runs when the TP5000 tells it to.

No, that's precisely right - you haven't missed anything.

The blurb says "Chrono-proportional cycling rates of 3, 6, 9 or 12 per hour can be selected."

The slowest rate thus has a 20 minute cycle - turning the boiler on for a proportion of this, and off for the rest. The fastest rate has only a 5 minute cycle. If it's like my Honeywell stat, there will also be another independant parameter which you can set in order to specify the minimum ON time - to prevent too much short cycling.