How to get weather compensation on Viessmann 100W working?

boccanegra · 28 Dec 2010

Hi,

I hope someone can help - I have a Viessmann Vitodens 100-W boiler and I am struggling to get the weather compensation working with it. Although the sales literature is full of descriptions of what the WC can do and how much it can save, it is short on how to make it effective, and neither the rep who sold my wife the system nor the installer were much more knowledgeable.

The system I have is:
• Viessmann Vitodens 100-W with WC module
• Horstmann ChannelPlus H37XL Series 2 controller
• Twin wireless thermostats (Drayton Digistat) – running a dual zone pipework set-up
• Viessmann Vitocell 200 cylinder
• TRVs on all radiators

My house is a detached, pre-1930s, non-cavity wall design and has lots of windows and although these are all double-glazed (and we have loft insulation in) the house lets out a fair amount of heat. Also, some rooms get markedly colder than others. Lastly, my wife is permanently cold so likes the temperature up!

The factors above meant that our previous boiler (an old, free-standing Potterton monster) guzzled gas by the shed-load and I am keen that the new system tries to reduce consumption to the minimum (hence going for the weather compensation etc). Having read the literature, it now looks like with our house we should have got the Viessmann 200, which has more sophisticated WC, but it is now too late for that.

My question is how to set up the various controllers etc so that the different rooms in the house remain at a reasonable, consistent temperature without burning more gas than is needed.

In particular:
• Does WC really mean the boiler should be on 24hrs a day as the rep seemed to imply to my wife? While I get that the system is designed to maintain a stable temperature, I assume it can’t use less energy that way than, for example, switching the system off at night and then turning on in the morning to heat the house?
• How, if at all, are the Drayton thermostats and the dual zones compatible with the WC? And can I set the two zones to different temperatures, controlled by the WC?
• How (if at all) do the various controls work with one another? I think the various controls we have are overkill on the system except for the WC itself (which is too simple) but would appreciate any help.
• The WC thinks that the house should be at a low temperature (I guess this is because of the heat loss). The operating instructions say you can “position (or shift) the heating curve so the boiler achieves and maintains the preferred temperature of the householder” but it’s not clear how you increase this temperature, unless it is simply by increasing the temperature of the hot water?

Any thoughts gratefully appreciated.

Thanks a lot,

Simon

Kev F · 28 Dec 2010

dont even attempt this yourself best to get someone in who knows, you need the outdoor sensor plus wiring loom, id use the wireless programmable stat they make and you will need a cylinder control box. it really is hard to explain let alone do it yourself if you dont do this sort of thing regularly

boccanegra · 28 Dec 2010

Hi,

As far as I know, the system has been set up and installed correctly (sensor in place, wiring etc). My questions were about controlling the system.

In particular, whether the WC would override the other controls or not and whether the heating needs to be on 24 hrs a day.

My assumptions (which are not a professional's and are therefore probably wrong) were:

* The WC sets the water temperature going through the pipes based on outside temperature with its estimate of what temperature in the pipes is needed to maintain a given temperature inside
*The main way to adjust the inside temperature is therefore to turn up/down the "base" temperature around which the WC varies
*The thermostatic controls in the two zones simply turn the flow of hot water on or off to that zone. So in effect they can can only turn the temperature down vs the main temperature that the WC is looking to maintain by switching off the boiler (because the WC when "always on" only gets to its target temperature)
*The TRV on the radiators can then further turn down individual radiators
*The programmer sets the whole thing on or off. This is only of any use if the system does not need to be on 24hrs a day
*Therefore, the way to set the right temperature is with WC on and the thermostats set to max and the TRVs to max to set the water temperature on the boiler so that the right temperature is achieved in the coldest rooms. Then to turn down TRVs to even out the temperatures in the rooms. And then to use the main two zone thermostats to adjust the temperatures in the different zones.

This is almost certainly a wrong interpretation, though, isn't it? And still I don't know if I need the system on 24hrs a day.

Any input appreciated.
thanks,
simon

mysteryman · 28 Dec 2010

Pretty well everything you say is correct. The weather compensation on a Vitodens 100-W is only really suited to a well insulated modern house, and you should have had a 200-W with its better weather comp.

You will need to keep the radiator knob on the boiler turned well up in severe weather, but you could lower it a bit in milder conditions.

ianniann · 28 Dec 2010

You may have to adjust your concept of "on 24 hours a day". Modern heating systems are designed to be on continuously and then controlled by a thermostat. At night, and possibly during the day, the thermostat will use a setback temperature which is lower than when you are at home enjoying the warm ambience. Very possibly the setback will mean the boiler does not fire at all during those periods except in very cold weather. Are your zone thermostats like this, with different temperature settings at different times of the day? If not, then forget what I said and just expect your system to be off at night and on when you need the house warm (and for a little while before).

As I understand, the 100-W system features a fixed flow temperature/outside temperature curve. This may mean that you find the system rather slow to heat up your poorly insulated house. In severe cases it could become unusable, but most likely it will work OK when you keep the house near the set temperature for long periods. You may need to adjust the setback periods so that the house has plenty of time to warm up to the living temperature.

You probably shouldn't worry too much about the complexities of this system. It is nothing different to you turning the boiler knob up a bit in winter and down a bit in spring, except that the controls do it continuously and automatically based on the outside temperature. Your boiler will produce hotter water in cold weather, but other than that you have a perfectly normal set of boiler controls.

So most of your trickiness is adjusting the two zones and the various TRVs to keep each room at the right temperature. You have little choice except to set the TRVs based on how warm you want each room to be. Rooms you prefer cooler can have a lower setting, rooms you want warm get a higher setting. Don't try to use the TRVs to control how fast a room heats up, that will be a disaster. You can, within limits, balance the radiators to send more heat to rooms that are less well insulated or have smaller radiators although the best solution is to size the radiators correctly for each room. Set the zone thermostats to a temperature that allows each room in that to warm up to the desired temperature, and ideally that will also be the right temperature for the area with the stat.

Agile · 29 Dec 2010

If the rep, the installer and you know little about this system then it follows that you needed someone to specify and set it up who knows rather more.

Of course Viessmann say that their boiler is fine with weather comp ! One of the comments above rather disagrees.

Properly designed and set up AND USED I would expect that reasonable resusts could be obtained.

Tony

ajrobb · 29 Dec 2010

I suspect you know the answer already. Use your ears...

Turn down the boiler setting gradually (one step a day) until you hear complaints then turn it up one.

In a solid-wall house like yours, running the heating for a minute extra is going to use more gas. Running the heating 24x7 (continental style) is going to use much more gas in a poorly insulated house than condensing can save.

In contrast to our old poorly insulated houses, in my sister's house in Sweden 30 years ago it was -20°C outside and I turned the room thermostat down when I went out for a few hours thinking I'd save some oil. When I came back, the temperature inside had hardly dropped! Incidentally, the room thermostat didn't control the boiler directly, it controlled a small electric heater (a light bulb) that controlled the boiler output temperature. The longer the light was on, the higher the flow temperature became. The longer it was off, the lower the flow temperature. I suppose it was an early form of weather compensation.

D_Hailsham · 30 Dec 2010

boccanegra said:
The system I have is:
• Viessmann Vitodens 100-W with WC module
• Horstmann ChannelPlus H37XL Series 2 controller
• Twin wireless thermostats (Drayton Digistat) – running a dual zone pipework set-up
• Viessmann Vitocell 200 cylinder
• TRVs on all radiators

Do the zone valves just open/close as instructed by the Digistats, or do they also control the boiler?

Are the Digistats just thermostats or are the programmable stats?

If you have TRVs on all rads how will the Digistats work? You should set the TRVs to Max in the room which has the Digistat.

Also, some rooms get markedly colder than others. Lastly, my wife is permanently cold so likes the temperature up!

Set the TRV in the coldest room to Max and then adjust the boiler temperature so that room reaches the required temperature. You should then find that the TRVs in the other rooms will keep them at the correct temperature.

Does WC really mean the boiler should be on 24hrs a day as the rep seemed to imply to my wife? While I get that the system is designed to maintain a stable temperature, I assume it can’t use less energy that way than, for example, switching the system off at night and then turning on in the morning to heat the house?

It all depends on how quickly your house loses heat and how quickly it heats up. The energy used to maintain a house at 20C for 7 hours over night may be less than that required to heat it up from 10C within an hour. Experiment. A Max-Min Thermometer is useful here.

How, if at all, are the Drayton thermostats and the dual zones compatible with the WC?

Were the zone valves there before you fitted the WC boiler?

And can I set the two zones to different temperatures, controlled by the WC?

The WC just controls the temperature of the water circulating through the rads, it does not control the zone valve. That's the job of the Digistat.

How (if at all) do the various controls work with one another? I think the various controls we have are overkill on the system except for the WC itself (which is too simple) but would appreciate any help.

I agree that the system is overkill as currently configured.

1. Why temperature controlled zone valves? I could understand if they were time controlled, so you could then stop heating a zone when not used. But temperature control can easily conflict with the TRVs.

The WC thinks that the house should be at a low temperature (I guess this is because of the heat loss).

But you said you have a high heat loss, so I would expect the water temperature to be high.

The operating instructions say you can “position (or shift) the heating curve so the boiler achieves and maintains the preferred temperature of the householder” but it’s not clear how you increase this temperature, unless it is simply by increasing the temperature of the hot water?

Yes. it's as simple as that. You just turn the boiler temperature up (righthand knob) until you get the required temperature.

Bunnyman · 30 Dec 2010

Ajrobb. An early form of an optocoupler as used on the early non hybrid Vaillant vow 242 mother boards ! Shine a light switch it on light goes off switch it off

Untitled

Bunnyman
26 Mar 2010
499

thecrazyplumber2000 · 7 Jun 2011

Hi. As a Viessmann trained and approved contractor can probably help. Firstly I need to know if it is Viessmann 100W combi, system or compact boiler. Also if it is a compact, is it running hot water and heating through a mid position 3 port valve or two 2 port zone valves?
Chris.

boccanegra said:
Hi,

I hope someone can help - I have a Viessmann Vitodens 100-W boiler and I am struggling to get the weather compensation working with it. Although the sales literature is full of descriptions of what the WC can do and how much it can save, it is short on how to make it effective, and neither the rep who sold my wife the system nor the installer were much more knowledgeable.

The system I have is:
• Viessmann Vitodens 100-W with WC module
• Horstmann ChannelPlus H37XL Series 2 controller
• Twin wireless thermostats (Drayton Digistat) – running a dual zone pipework set-up
• Viessmann Vitocell 200 cylinder
• TRVs on all radiators

My house is a detached, pre-1930s, non-cavity wall design and has lots of windows and although these are all double-glazed (and we have loft insulation in) the house lets out a fair amount of heat. Also, some rooms get markedly colder than others. Lastly, my wife is permanently cold so likes the temperature up!

The factors above meant that our previous boiler (an old, free-standing Potterton monster) guzzled gas by the shed-load and I am keen that the new system tries to reduce consumption to the minimum (hence going for the weather compensation etc). Having read the literature, it now looks like with our house we should have got the Viessmann 200, which has more sophisticated WC, but it is now too late for that.

My question is how to set up the various controllers etc so that the different rooms in the house remain at a reasonable, consistent temperature without burning more gas than is needed.

In particular:
• Does WC really mean the boiler should be on 24hrs a day as the rep seemed to imply to my wife? While I get that the system is designed to maintain a stable temperature, I assume it can’t use less energy that way than, for example, switching the system off at night and then turning on in the morning to heat the house?
• How, if at all, are the Drayton thermostats and the dual zones compatible with the WC? And can I set the two zones to different temperatures, controlled by the WC?
• How (if at all) do the various controls work with one another? I think the various controls we have are overkill on the system except for the WC itself (which is too simple) but would appreciate any help.
• The WC thinks that the house should be at a low temperature (I guess this is because of the heat loss). The operating instructions say you can “position (or shift) the heating curve so the boiler achieves and maintains the preferred temperature of the householder” but it’s not clear how you increase this temperature, unless it is simply by increasing the temperature of the hot water?

Any thoughts gratefully appreciated.

Thanks a lot,

Simon

Bunnyman · 7 Jun 2011

Hi mate I c ur new check the dates this thread finished 6 months ago

Untitled

Bunnyman
26 Mar 2010
499

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

How to get weather compensation on Viessmann 100W working?

mysteryman

Similar threads