Veissmann Vitodens 200 ...

[Dave Plowman (News)]

Finally finished off the installation by fitting the weather compensation kit and remote programmer. The last bit because the boiler is in the bathroom and I'm used to having the programmer handy in the kitchen. Expensive convenience, though.

All I can say is thank gawd Viessmann have a technical department you can actually talk to and know their subject.

With the original programmer it worked fine straight out of the box - it has factory settings which do for a start. But not the other two. Got a fault light with the weather comp one. Although it seemed to work ok. Phone the tech dept. Got told how to code it - about 5 steps - and not referred to in any of the many handbooks. Unless perhaps you understood everything already. So far so good. Was a bit chilly in the evening so switched the heating on. (The hot water was fine) Nothing. Pump running but no heat. Phoned them up again this morning. Had to alter the weather comp gradient. Think this might be a steep learning curve...

The engineer said there's no need for any internal thermostat since the programmer has a temp sensor. He reckons properly set up the outdoor one will do all that's needed. I'm not convinced since the temp in the kitchen will vary far more than where the original is - in the living area. At the moment that is the original programmable type - no longer needed since the boiler controller can do all the time/temp settings so I'm thinking of fitting the Viessmann room temp sensor in its place. Any comments from someone with this system or similar?

[Andy Hall]

Did you put the weather compensation sensor on a north facing wall, or at least where the sun won't fall on it? This is fairly important because it should be sensing the ambient temperature and not the result of the sensor being hit directly by the sun. It would give an artificially high reading.

Do they have a handbook that documents in detail all of the engineer menus? It would be surprising if a German boiler manufacturer didn't document these details somewhere, but possible that it's in a different one to the installation and certainly the end user guides.

On mine (MAN Micromat) there are engineer settings to control whether the weather sensor is taken into account and then settings for end points of temperature, offsets and slope. These concepts are pretty much the same for all boilers that include integral weather compensation - i.e. have a sensor that can allow the boiler's controller to determine the actual temperature outside.

I went through almost the same steps. The boiler has an integral programmer that can handle the time settings. It has inputs for the weather sensor and a similar temperature sensor for the HW cylinder. There is a further input for a room programmer or thermostat.

The HW cylinder sensing can be set to use the temperature sensor, in which case the boiler can determine the HW temperature and operate to give good control. ALternatively it can be set to use a simple cylinder thermostat.

The room controller input can be similarly set. The boiler can work without it at all, can use a conventional switched programmer/thermostat or can use an intelligent proprietary external programmer and temperature sensor.

Initially, I used the weather compensator, the boiler's internal time setting and TRVs on all radiators. This did work quite well. Later I added the external programmer and room temperature sensor (these are both in the same unit). This unit also has a user accessible setting whereby the balance between the influence of the weather compensator and the internal sensor on the boiler's behaviour can be adjusted. This appears to be a fairly fine adjustment because it's clear that even if set to the room sensor end of the range, the weather compensator still affects behaviour. E.G. if the outside temperature drops rapidly, the boiler is starting to react before the inside temperature would be starting to fall.

So I think that it is worth having the inside measurement, but as you say, measuring the kitchen temperature is not really the useful place.

I'm sure that you've played around with op-amp circuits qute a bit. All of this is very much akin to adjusting gain, offsets and output swing limits with these. Now imagine having two circuits that have considerable time constant slugging and combining the output of these proportionally. This is roughly what you have.

The settings have to be determined experimentally.....

[John Rumm]

Or modelled in pSpice or similar...

[Andy Hall]

Is that still free now that Cadence are involved in it?

[John Rumm]

Not looked... but there are plenty of Spice versions that are.

[Donwill]

No, but I'm hoping to install the same this year so am very interested in your experiences, and hope you will pass on all relevant information. In a past home I installed an oil boiler with a Honeywell AQ 6000 controller which controlled CH temp on the external temp sensor, but also had an internal sensor. The system was self learning so it would adjust gradually over a period of days to control on the ext temp allowing for building heat loss and thermal inertia. In practice I found it to be a superb system. I'm hoping the Viessman will give similar results. Regards Don

[Dave Plowman (News)]

If you're DIYing the install I can certainly pass on my gotchas.

I'm told this does the same.

Hopefully it will.

[Dave Plowman (News)]

A north facing wall would mean the front of the house - and a bit of a pain wiring wise. It's on a west facing one. Really the only practical place for it.

It's in a white box. ;-)

It does - but scattered over several. There's an installation one - a service one - and sundry others for the upgrades. A real hotch potch.

Mine can only use the Viessmann sensor. An expensive extra.

I can use an ordinary room stat - indeed that's what I've done. Which all worked fine until I fitted the weather compensation upgrade - which consists of a complete new programmer to go with the external sensor.

Indeed. Luckily I should have some time to suss it out before it's needed in anger. Assuming I can afford the gas then.