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Vitodens WWSD Operation

Finally have an approximation of warm-weather shutdown. Continuous circulation with TRVs and 11°C (20°F) reset shift, so boiler continually wanted to make heat even when not needed by the house.

Outside temp is solar influenced--it turns yellow during times of peak influence.

Supply target is based on curve in boiler--it does not come directly from the boiler but does agree very closely when the sun isn't shining hard at least ;)

Rather strange way to get the thing to go into WWSD. You use the "External Switching of Heating Program" function. You set address 011 to 001 and 0C8 to 000, then connect your DRY contacts to X4.1 & X4.2

When the DRY contacts are closed, "Telephone Prog" appears in the display and the boiler runs at the NORMAL room temperature setting. Am guessing that the expected use of this function is for a vacation home or similar where you "telephone for heat" as the boiler is assumed to be at the reduced temperature setting.

So, for me to use I had to remove all normal/reduced program timing (this keeps the boiler in REDUCED temperature mode at ALL times). Then, use the normally closed contacts of the WWSD. Whenever outside temp is below the changeover point, the contacts are closed and the boiler runs in normal room temp mode. When outside temp rises, the contacts open and the boiler reverts to reduced room temp mode.

My reduced temp mode setting is 52° and changeover point is 55° so with outside temp ALWAYS above desired room temp the boiler seems to go into "standby". 32° is displayed as the target temperature and the circulator stops. Supply target on the graph changes to dashed blue to reflect the setting.

A second outdoor sensor for the boiler will be coming soon. Am going to mount it on the South side of the house and flip-flop between the two outdoor sensors (via gold-plated relay contacts) when solar influence is high but outdoor temp not too low.

Goal is to shift the WWSD point based on solar influence. On a nice sunny day, it should switch over at around 50° (measured on the North) but will still switch over at 55°-60° in cloudy weather.


  • Glen
    Glen Member Posts: 855

    Mike -

    As 4.1 and 4.2 only respond to the closing of dry contacts (eg external call for heat or shutdown) and I have looked at these contacts/programming addresses too. Why don't you use a stat to close the contacts - and then you would have a floating point with which you can experiment. I think close on temp rise would work nicely.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    The WWSD has a variable setpoint like a thermostat--it just uses a remote bulb sensor. Seems to have about a 5° differential. Believe it was actually made for some sort of refrigeration application as setpoint varies from about minus 20° to 70°. It also has both normally open and normally closed contacts.
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