Viessmann boiler question

[mars_man]

Hi I have had a similar problem with a similar boiler that was caused by the boiler always trying to achieve a temperature differential of no more than 20 degrees between the flow and return. If greater than 20 degrees the boiler simply cuts out. As crazy as it seems it was designed to do this. Viessmann recommended replacing the pcb since they have been made aware that this is causing problems for many users and have changed the internal boiler control algorithm on the new pcb. Yours might be dping a similar thing. I would suggest contacting Viessmann who I'm sure would be happy to help. One additional note - if this is the cause of your rads not reaching temperature be sure to check you have a decent flow through the boiler first, since restrictions in flow will cause a greater temp differential. Best of luck and please post omce you get to the bottom of it so we can all learn.

Viessmann hasn't come back yet . They did offer to troubleshoot over the phone which I didnt want .
This boiler is now 2 months old , how old was your when you had this problem ?

 

[Joe.R]

A bit late to the party, but I have had a similar issue in my own house. The Vitodens replaced a 15 year old suprima in December.

The heating took quite a lot longer to reach temp, and I put this down to the weather compensation curve, however, the hot water cylinder went from 40 min reheats to 2 hours + (with the hot water relay for weather comp it’s target temp becomes 80 degrees)

Turned out it needed a low loss header. System works exceptionally well now, no cycling and quicker to heat (sub 25 min reheats on hot water, and 3 hours less on heating to reach 20 degrees - with flow temp that seems to average 55 degrees). I thought it was a little overkill for a 1930s semi, 20 rad, 1 unvented cylinder system...but...it cured the issue. Also, there are three heating zones on this system too - ground, 1st & loft.