Running the pillefyr for DHW production only is a bit of a challenge, as the NBE manual as quoted by Michael (but not the NBE sales brochures
) demonstrates. Three constraints: (a) Boiler temps should not be too low as there will be condensation @47C or lower as per the NBE manual (and you'll want a bit of a safety cushion - none of the temperature feelers are calibrated); (b) boiler should dry out between starts if not constantly on; (c) there is a calcification issue if the water in the VVB heat exchanger gets too hot.
I'm not sure what you mean by "minimum" and "maximum" boiler temp. Do you mean 55 is the "wanted" boiler temp and 70 is the temp where it switches off? If so, at what temp do you switch it on again (the "difference under")?
In any case, as Michael says installation of a temp feeler would be best. If you don't have the option to use a pipe in the VVB for this purpose, or the VVB pipe does not allow you to install the temp feeler at the right height - approx. 50% of the VVB (the actual water reservoir) height -, you can drill a hole in the outer (!) VVB hull, push the temp feeler through the insulation against the water reservoir wall, and fix with PUR foam or similar).
In the meantime, you may want to consider using the DHW timer function. You can set the desired boiler temp to 65C, shut it down if it's, say, 5 or 7K above, and have it restart when it's 5K below. I'd also have it start the pump at 63C (there is an undocumented feature in the SW that shuts off the pump again if the temp drops 10K below that value, which is helpful in some circumstances) and shut it off at 63C as well. But all these settings will only apply during the period(s) when your timer is active. Start with, for example, four hours a day (e.g., 0500 - 0900) and see if that works for you. The objective should be to have the boiler start up once during one timer period and have it fully "charge" the VVB. You may also have to play with the P and I DHW regulation factors for this to work.
Good luck,
Karsten
