Vitodens 200 with weather compensation uses a graph to determine the flow temperature from the outside temperature. The limitation of the flow temperature leaves thermostats at heaters open. This saves energy to circulate the water through the heating system.
Vitodens with weather compensation uses no thermostat to measure the room temperature. It assumes by supplying a certain flow temperature to reach a target room temperature. All you need to get right is the level and slope of the graph. These parameters depend on the house type.
With the right parameters this approach will hold the target room temperature once the target temperature has been reached and the parameters do not change because of bad insulation (e.g. drafts from wind).
- there is a minimum interval between two burner ignitions of 4 minutes which cannot be changed
- the hysteresis between the flow and return flow is fixed and cannot be changed
What you see happening is: the controls magically determine that the burner needs to ignite. A certain high gas input has to be provided for the ignition, then the burner reduces. Often the flow temperature quickly rises because the return flow is still hot. The burner switches off after less than 2 minutes. Then the burner is blocked for 4 minutes until the game starts again. After a few such cycles it eventually will happen that the return flow is cold enough and the burner will fire a few minutes longer. This easily leads to 150 burner starts within 18 hours for a normal room temperautre of 20 degrees celcius and outside temperatures btw. 0 and 10 degrees celcius. Assuming 100 days of heating per year this leads to approx. 15000 ignitions per year. causing damage to the gas valve and the relays on the board. With the needed high gas input for the ignition and the short circulation of less than 2 minutes, most of the heat does not get to heaters. Viessmann may tell you to balance the heating system, but that will not solve all issues.
The issue with this design is:
- fixed slope and level does not work for badly insulated houses, e.g. in Ireland and England, houses are badly insulated and there are drafts in the house. I.e. with strong winds hotter flow needs to be provided, i.e. there needs to be a set of slope/level for windy days
- missing thermostat in the house (all depends on the chosen slope that is determined by experiment)
- too short time between ignitions (the heat needs time to distribute)
- the graph determines the flow temperature to keep the inside temperature at e.g. 20°C for a specific outside temperature. There is no information what the flow should be if the temperature ever fell below 20°C.
- after a reduced temperature (e.g. in the night) the flow temperature must be increased until the 20°C are reached.
The start limiter reduces the number of burner starts to 15 and less and the average burner on time is 20 to 50 minutes. All heating controls remain working as before.