Vaillant weather comp - lower heating curve = less gas used?

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I have a wall mounted Vaillant VRC 430 (and Ecotec 618 and Unistor - with VR10 - running through the VR65 control box).

This autumn, I have had a full loft conversion to current regs which has greatly improved the insulation of my Victorian mid terrace.

Prior to the conversion, I had the heating curve set to 2.8. Once the conversion was finished, I reset the VRC 430 to try and wipe its 'memory' - it is set to modulate with respect to the room temp, and I wanted to allow the unit to recalibrate to the heatinh response of a much better insulated house.

Since the completion of the conversion and the recent cold weather, I have experimented with reducing the heating curve as far as 1.9.

This has obviously reduced the flow temps, and the set temperatures have been maintained. However, the boiler seems to spend longer firing.

Questions:

1) Does lowering the heating curve reduce energy consumption?
2) Why do Vaillant recommend such a high (expensive) heating curve for the UK?
3) What heating curve does any one else (installers/users) recommend?

thanks
 
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Have the heating curve as low as you can while still providing adequate heat. The lower the curve the longer the boiler will condense and the more efficent it will be. Has the boiler been range rated using d0? I would also suggest the following; d1 to 8, d71 to 70.
 
I think that you should try to better understand what the WC is doing!

The outside sensor output is used to compute how much heat, in the guise of the flow temperature, is likely to be needed to heat the house to your desired temperature.

Many of the WC systems are in my view rather lacking because they do not monitor the INSIDE temperature. What they seek to do is compute the heat loss and supply that amount of heat.

Having said that most work very well and give a saving by lowering the flow temperature when less heat is required thus enabling the boiler to condense more.

If the flow temperature is lower then more time is required to heat the inside up. With a better insulated house a lower setting may be adequate.

Tony
 
Have the heating curve as low as you can while still providing adequate heat. The lower the curve the longer the boiler will condense and the more efficent it will be. Has the boiler been range rated using d0? I would also suggest the following; d1 to 8, d71 to 70.

Boiler was range rated to 15Kw, and also d1 already set to 8mins.

Have reduced max heat flow (d71) as suggested - many thanks.
 
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I am the proud owner of a VRC430 which is set as a roomstat in my main room. The boiler is an EcoTec 415 open-vent boiler fitted in a fairly standard Y-plan setup via a VR65. House is small 3 bed semi with cavity insulation etc.

I'm a retired person and very keen to be economical with the gas for financial reasons as well as carbon footprint. I only heat the living room, kitchen and bathroom as a matter of course and usually only to 18C.

I have had ever such a time getting this to work acceptably. I have spent solid weeks measuring, theorising, writing to Vaillant about what they should do to make the boiler work better, modifying the plumbing and tuning. In the end, I have a workable solution with limitations.

I'm now using a heating curve of 1.5 which is down from 2.5 in the early days. I also have the minimum temperature set in the VRC430 to 45C because it doesn't work at all at lower temperatures. With these settings, steady temperatures are well maintained but it is hopelessly unresponsive. I believe that there is no alternative to trickery to get it up to temperature in the morning or to raise the temperature rapidly at other times.

Your questions:

1) Does lowering the heating curve reduce energy consumption?

I have seen graphs showing that there may be up to 8% more efficiency from running at a return temperature of 30C as opposed to 50C. This related to some sort of generic condensing boiler but is an indication that there is something there worth going for. The fact that the boiler runs for longer should not be relevant apart from energy consumption in pumping and any losses in the pipework which don't contribute to the heating of the house. Room temperature should be contained within a narrower range.


2) Why do Vaillant recommend such a high (expensive) heating curve for the UK?

I think it is because they have found that this is more likely to work for their customers so that they get fewer complaints. They would probably say that their boilers are very efficient at high temperatures anyway. My own analysis is that there is a "feature" of the Vaillant boilers operation which is challenging in low temperature operation and this may well be common to other manufacturers. The difficulty is possibly most apparent in smaller and/or better insulated homes. You may have noticed that when the boiler fires up it runs at a fairly constant rate for about the first minute. My boiler is rated to modulate between 5 and 15 kw. In the first minute, it runs at 12kw. Given the minimum acceptable flow rate through the boiler, that gives a rise of about 16C. If the heat requirement of the house falls below 5kw the boiler has to cycle. Once the boiler has switched off, it cannot start again until the return water has fallen to about 15C below the target flow temperature. This is quite quick at high temperatures but it gets increasingly slow at lower temperatures. The details will vary with every installation. In my house, at 70C it takes 10 minutes, at 45C it takes 35 minutes. This is made more difficult because the VRC430 reduces the target temperature as room temperature rises and also if the outdoor temperature rises. This is what happens in the morning. So successful restart is even further delayed. Setting d2 so that the retries (which are time based) have a chance of succeeding is a challenge.

My radiators are on microbore (I upgraded to 10mm for the large living room rad) so a significant proportion of the water going through the boiler goes through the automatic bypass valve and staight back to the boiler. This leads to a bad effect of unsuccessful restarts - they delay the possibility of a successful start while the extra heat is dissipated. I have now worked out how to avoid failed starts - set d2 to 60, d1 to 38, keep the kitchen radiator on and don't try temperatures below 45. I changed the pump to a more powerful 6m head model to get more flow and added a well-insulated 3.6 litre radiator into the bypass circuit to stop the heated water getting back to the boiler until the first minute is up and the boiler is ready to modulate down to 5kw.

All in all, it is much simpler to set a high heating curve. Lower efficiency and lumpy heat delivery are the consequences.



3) What heating curve does any one else (installers/users) recommend?

I would agree with some of your other posters. The lower the better while it continues to keep you warm and is responsive to changes. When I bought this kit , I thought that 5-15kw modulating would mean what it said and I had sized my radiator to work at about 1.2 heating curve. I was horrified by my early experiences but I'm fairly pleased that 1.5 works quite well. I doubt I will notice any effect on my gas bill which has been low throughout because the house and boiler are quite efficient.
 
Hi MHOL, I realise it has been some time since you posted, but I'm having similar problems, with a similar system.

I have an ecoTEC plus 637 system boiler, an external thermostat, a VRC430 thermostat located in the hallway and a VR65 connecting everything together.

I've been working at home this week and noticed that the house gets quite cold during the day, with the radiators being luke warm to warm, whereas in the evenings the house feels warmer and the radiators are red hot.

At 15:31 on a Tuesday afternoon, the VRC430 is showing an external temperature of 13 C, internal temp of 18 C, however it is set to reach 21 C, which it rarely ever does, unless it is a hot sunny day!

The heating curve is set to 1.5, which was set by the installer. I'm guessing that I need to increase this to increase the temperature during the day, but I don't want the house to be any hotter in the evenings!

Based on your experience, have you any thoughts on how to tweak my system?
 
I think that you should try to better understand what the WC is doing!

The outside sensor output is used to compute how much heat, in the guise of the flow temperature, is likely to be needed to heat the house to your desired temperature.

Many of the WC systems are in my view rather lacking because they do not monitor the INSIDE temperature. What they seek to do is compute the heat loss and supply that amount of heat.

Having said that most work very well and give a saving by lowering the flow temperature when less heat is required thus enabling the boiler to condense more.

If the flow temperature is lower then more time is required to heat the inside up. With a better insulated house a lower setting may be adequate.

Tony

with vaillants weather compensation you can monitor room temperature too as long as the controller is not mounted in the boiler...

you just have to change a parameter
 
As I said, the thermostat is installed in the hallway (the coldest area of the house). It shows both an external and internal temperature, but the internal temperature is 3 degrees C below the programmed, required temperature.

I understand that the external thermostat is having an effect on the internal temperature, my problem is it appears to be having too much of an affect such that when it's really cold outside, the house warms up nicely, but when it gets milder (13 degrees C today according to the outside thermostat), then this results in the heating not being warm enough.

I suspect increasing the heating curve might help this, but I'm not sure and I can't find any documentation showing the effect of the various heating curve settings.
 
I would look at balancing firstly to ensure that all radiators get evenly hot..

what is your set back temperature and is the controller set to energy saving, frost protection or eco mode...

Is the room control strategy set to modulating, none or thermostat..

it may be that you are just relying on outdoor temperature sensing when you could benefit from indoor temperature sensing too. You need to enter installer level to set the controls to take in to consideration the indoor temperature...
 
The only "set back temperature" setting I can see on the VRC 430 is the night set back temperature, which is set to 15 C. During the day (between 6:00 and 23:00) the temperature is set to 21 C, but never reaches this and is usually around 18 to 19 C.

As for the other functions you mention, I have no idea how to tell if they're set or how to set them. I've checked the Vaillant Owner guide and it doesn't mention them!

As for getting into the installer menu, I haven't been shown how to do this.

Do Vaillant produce any decent documentation that explains these features, when and how to use them, or is this type of documentation reserved for engineers?
 
Alec....thought you had Vaillant fix the 400's do that WC works below 45flow?

MHOL.. Your not the guy that wrote the blog and that Alec said was suing him are you?
 
I doubt I could get vaillant to do anything.. but the issues on my clients 400 series boilers have been resolved by vaillant themselves...
 
Would it not be wise then to enlighten MHOL as he currently believes it doesn't work below 45 when you know different.
 
He has a 637, which works fine with the 430 and other modulating controls. The issue can be resolved by making adjustments as I suggest.
 

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