Thanks, I have that manual, and I used the graphs on pages 18/19 to try various different settings. Now back to Slope 1.4, level 0.
Pages 18/19? Don't you mean pages 68 to 70?
Hopefully, as a competent engineer, you have kept a record of what effect your experimental changes have had. Could you post that information?
Do you know the system design parameters - outside, flow and room temperatures? Typically, in the UK, they are -1C, 75C, 20C, which will require a slope of 2.4. Modern systems, designed to make maximum use of condensing boilers may use lower a flow temperature. Different outside and room temperatures may have been used.
Weather compensation does assume that rads have been properly sized for the heat loss. So if some of your rads are giving off much more, or less, than is required you may have difficulty setting the correct curve and offset.
You say that the outdoor sensor is "under the eaves". This is contrary to Viessmann's instructions, which say:
• North or north-western wall, 2 to 2.5m above ground level; in multi storey buildings, in the upper half of the second floor
• Not above windows, doors or ventilation outlets
• Not immediately below balconies or gutters
• Never render over
• 2-core lead, max 35m length with a cross-section of 1.5mm2
NB "second floor" is what we, in the UK, call the "first". Viessmann, like all Europe and America, call the ground floor "first".
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