Something odd happening

[Norfolkboy]

hi norfolkboy, I think from your previous messages we have the same system setup, viessman wb1b opentherm. I occasionally get those low flow temps as well, but it only seems to be at a time when you would think the is a possible reasone.g. only 1 room on, and its within 0.5 of setpoint, so its just using those last few therms before it fires the boiler again. my system has been in a year so learning all done. I have also seen it happen late at night, all rooms setpoint of 15, one has cooled to 14.5. so it pumps 30 degree water round and squeezes that 0.5. Just seems to be what OT does with this boiler.

I do also get that odd "switch off then back on" but it doesn't happen often enough to matter / doesn't make a difference to the practical behaviour so I have stopped worrying about it. Glad I'm not the only one who that has a new hobby of watching the boiler working!

FWIW, I spent the first 6 mo of the system being in standing for many hours in a corner of the kitchen where I could see both the boiler screen (other end of utility room) and the evo controller (hall) , with a notepad... so your keen-ness to watch whats going on after only 10 days is very understandable!

Thmaks for you update, yes we have the same system, but weirdly mine didn't required the hot water demand box, OT seems to up the flow temp to 78c when hw is on. Must be a firmware difference?

[Norfolkboy]

It was OT that forced me to get some boiler diagnostics going. No way was I going to run into the Loft numerous times a day to check what the Flow, Return and Target Flow were. You guys are lucky, I can't say I'm completely happy with the OT implementation on the Vaillant boilers with the VR33. The OT seems to run the boiler too much at the max even when there is no HW demand. Yes, sure enough, it isn't simply toggling between max and off now, but I was expecting the boiler to run at a much lower temperature when there was only CH demand.

I'm come to the conclusion that OT is not 100% reliable in the way is talks to the boiler, doesn't seem that the "common" language used is translated correctly all the time- flow temp is good on mine but the random switching off of the pump is annoying!

[sandyman]

Thmaks for you update, yes we have the same system, but weirdly mine didn't required the hot water demand box, OT seems to up the flow temp to 78c when hw is on. Must be a firmware difference?

really? so your only control input to the boiler is OT, when evo calls for hot water over OT, you get the tap symbol on the boiler screen and 78c flow? in which case must be a firmware thing, as mine in exact same config wouldn't do it. needed the extra hw input to the viessman to get 78 (hence why I told you you HAVE to get that extra box...)
would love to know whether its the evo OT box or the boiler or both thats been changed. have to keep firmware on so many things up to date, had never thought that could be the case with the boiler! would be really good if we could get someone from the boiler mfrs to pay attention to these forums (in the same way as the honeywell guys do) as there's plenty of valuable product improvement information in here for them.

[Norfolkboy]

really? so your only control input to the boiler is OT, when evo calls for hot water over OT, you get the tap symbol on the boiler screen and 78c flow? in which case must be a firmware thing, as mine in exact same config wouldn't do it. needed the extra hw input to the viessman to get 78 (hence why I told you you HAVE to get that extra box...)
would love to know whether its the evo OT box or the boiler or both thats been changed. have to keep firmware on so many things up to date, had never thought that could be the case with the boiler! would be really good if we could get someone from the boiler mfrs to pay attention to these forums (in the same way as the honeywell guys do) as there's plenty of valuable product improvement information in here for them.

I dont get the tap symbol, the rad one stays on but the boiler temp increases once Evo calls for hot water. it works if no heating is on or zones are calling for heat, it overrules the heating flow temp target. i now have a surplus heat demand box! luckily i picked up a 2nd hand one so didnt cost too much. I did add the box to start with but the the tap symbol would come on for 3 seconds and then go off but still reach 78c. OT must take priority over the demand box

My boiler was installed 12 months ago fyi, would be great to get some feedback from Viessman on the intrigration of Opentherm with their boilers

[sandyman]

OT must take priority over the demand box

My boiler was installed 12 months ago fyi, would be great to get some feedback from Viessman on the intrigration of Opentherm with their boilers

so my boiler is also 12 months old install, so you ought to expect they are same build!

not quite right on the priority (took me ages to find this first time round)

https://www.manualslib.com/manual/703223/Viessmann-Vitodens-100-W-Wb1b-Series.html?page=85

footnote 1 - highest of all input signals.

[richardc1983]

It was OT that forced me to get some boiler diagnostics going. No way was I going to run into the Loft numerous times a day to check what the Flow, Return and Target Flow were. You guys are lucky, I can't say I'm completely happy with the OT implementation on the Vaillant boilers with the VR33. The OT seems to run the boiler too much at the max even when there is no HW demand. Yes, sure enough, it isn't simply toggling between max and off now, but I was expecting the boiler to run at a much lower temperature when there was only CH demand.

Same with the lyric t6 and vogue. Ideal say that the min flow temp the opentherm will do is 45C yet you can select down to 30C manually on the boiler. Even running at 45C is too much output! 40C was what I set my old boiler to after house was upto temp!

[Norfolkboy]

so my boiler is also 12 months old install, so you ought to expect they are same build!

not quite right on the priority (took me ages to find this first time round)

https://www.manualslib.com/manual/703223/Viessmann-Vitodens-100-W-Wb1b-Series.html?page=85

footnote 1 - highest of all input signals.

Not quite as OT is priority 2 and demand box is 3, and as OT was calling for 78c heat as well then that would be still be priority, that's why the tap symbol did not appear on mine when dew was on