Why would a Viessmann boiler be commissioned with continuous operation mode?

[Adsibob]

We are away on holiday and have a friend checking up on the house. He called me up to tell me the boiler fan was running and some adjacent pipes were hot. At the time this observation was made, the thermostats in the rooms and HW for the cylinder had all been off for 30h at least.

 Fishing through the various menus on the Viessman (a Vitodens 200W system boiler), and consulting the manual it appears that there are three modes which it can be setup on initial commissioning: 

 

- weather compensated mode

- continuous operation

- room temperature dependent mode

 

Im just trying to work out if this was a mistake on commissioning or if there might be a reason for choosing continuous operation? We have our system boiler installed with a low loss header. All our heating is UFH (four manifolds) except in two bathrooms, where we also have a towel rad in each one.

 

My friend couldn’t seem to change the mode to “room temperature dependent mode”, so he has just turned the whole boiler off at the mains.

 

I will investigate when I’m back home, but it was commissioned 9 months ago and because we have the hot water tank heated by the boiler three times a day plus a recirculating secondary loop that comes on wherever you’re in the room where the boiler is, I had assumed the hot pipes were from that - never noticed the boiler make any fan noise when it was meant to be off, so I wonder if this is a mistake at the time it was commissioned, or an issue that’s developed since. 

 

I attach a screenshot from the manual; it doesn’t give much info:

 

 

[Mr Punter]

It is probably best not to get your friend to fiddle with the commissioning settings.  Maybe ask the engineer when you get back or when they service the unit.

[Adsibob]

2 hours ago, Mr Punter said:

It is probably best not to get your friend to fiddle with the commissioning settings.  Maybe ask the engineer when you get back or when they service the unit.

Indeed.

Just curious as to other’s thoughts on the utility of a continuous operation mode. Maybe @Nickfromwales will chime in with some views. 

[Adsibob]

@larry has the same boiler, so curious in what mode his was commissioned.

[Temp]

I'm wondering if the installer wasn't familiar with UFH and someone told him that the best way to run UFH was "continuously" so that's the boiler mode he selected !  

 

Presumably when none of your UFH manifolds or towel rads are calling for heat a bypass opens, the return temperature rises and that shuts off the burner?

Edited March 27, 2023 by Temp

[Nickfromwales]

1 hour ago, Adsibob said:

Indeed.

Just curious as to other’s thoughts on the utility of a continuous operation mode. Maybe @Nickfromwales will chime in with some views. 

Continuous operation as I read it in your screenshot means it just doesn’t attenuate flow temp a-La weather comp. Not that the boiler ( heat generator ) would run continuously? 
Was there a WC’p outside sensor installed also when the boiler was installed? If not, then that’s why it’s set to that. 
 

I would have thought room temp setting would have been the one, with the room stat dictating this? 
 

FYI, I’ve never worked on / been around an install for one of these. 

[Nickfromwales]

4 minutes ago, Temp said:

Presumably when none of your UFH manifolds or towel rads are calling for heat a bypass opens, the return temperature rises and that shuts off the burner?

If there is no call for heat, the 0v or 230v signal would drop and the boiler would go into pump overrun and then go into standby? If it’s a system boiler. 

[Temp]

13 minutes ago, Nickfromwales said:

If there is no call for heat, the 0v or 230v signal would drop and the boiler would go into pump overrun and then go into standby? If it’s a system boiler. 

 

That's what I would expect in Room Temperature mode but it doesn't mention being controlled by room stats (directly or indirectly via a wiring centre)  in the paragraph describing continuous mode. 

Edited March 27, 2023 by Temp

[Adsibob]

13 minutes ago, Nickfromwales said:

If there is no call for heat, the 0v or 230v signal would drop and the boiler would go into pump overrun and then go into standby? If it’s a system boiler. 

Yes, it’s a system boiler. There are thermostats for each zone, on timers. The boiler should only come on when a thermostat calls for heat. But this wasn’t the case on Saturday 30h or so after the last call for heat.

[Adsibob]

19 minutes ago, Nickfromwales said:

Was there a WC’p outside sensor installed also when the boiler was installed?
 

no.

19 minutes ago, Nickfromwales said:

 

 

 

 

If not, then that’s why it’s set to that. 
 

I would have thought room temp setting would have been the one, with the room stat dictating this?

don’t these two statements contradict each other?

[Temp]

Manual also has this..

 

Quote

 

Your system is preset
Your heating system is preset at the factory and is
therefore ready for operation following commissioning
by your contractor:

 

Central heating in weather-compensated operation
■ Between 06:00 h and 22:00 h, rooms are heated to
20 °C "Room set temperature" (standard room
temperature).
■ Between 22:00 h and 06:00 h, rooms are heated to
3 °C "Set reduced room temperature" (reduced
room temperature, frost protection).

 

Central heating in continuous operation
■ Between 06:00 h and 22:00 h, the set flow temperature
is 60 °C ("Normal set flow temperature")
■ Between 22:00 h and 06:00 h the set flow temperature
is 50 °C ("Reduced set flow temperature",
frost protection)

Central heating in room temperature-dependent
operation
■ The rooms are heated in accordance with the settings
on your room temperature controller.

 

 

Not sure it make things any clearer.

 

 

 

[Temp]

[Temp]

The only time I can think continuous mode might work is when you have a rad system with a TRV on every rad? and a bypass to shut the boiler off when they are all closed. 

 

Will be interesting to hear what the answer is.

[Lofty718]

Running a Viessmann 200W without weather compensation is a crime against humanity, any installer putting in one without weather comp is a cowboy. Has he set it up as a 4 pipe system with hot water priority like it's designed to be?

 

That's the whole reason the boiler is so expensive because it comes with weather compensation out of the box, It's like buying a Lambo and limiting the engine to 150bhp. Heating systems in Germany and Holland are mandated to be used with weather compensation, we are lightyears behind here

 

Viessmanns are best run continuously at a low flow temperature, with no room thermostats and the ufh manifolds should be low temperature ones controlled by electronic mixing valves not the crappy high temp one on the manifold

 

I've never owned a Viessmann but my Vaillant has holiday mode I'm certain Viesmmann has the same.

 

 

Edited March 27, 2023 by JoeyF

[Adsibob]

1 hour ago, Temp said:

Thanks @Temp, this just makes me think it should have been commissioned in room temperature-dependent mode.

[Lofty718]

@Adsibob You'll see the manual refers to mixed circuits, which is how Viessmann intends their systems to be used with mixers like below.

 

 

https://viessmanndirect.co.uk/Catalogue/Divicons-and-Mixers/Divicon/Divicon-with-Mixer-Extension

 

*can be found much cheaper than this though*

 

could you post a pic of your boiler setup?

Edited March 27, 2023 by JoeyF

[Nickfromwales]

17 hours ago, Adsibob said:

no.

don’t these two statements contradict each other?

Er, no?

If no WC'p sensor, it would default to continuous as it could not be commissioned. It would show an error code if trying to select WC'p mode, Shirley?

 

Albeit, yesterday was a bit of a blur.

[Nickfromwales]

Thanks @Temp

Seems that continuous mode uses either comfort or economy temps, and doesn't actually shut off. I expect having DHW and a HRC running when in residence has masked this occurrence.

Case closed. "Watson, fetch me my pipe!".