Vaillant EcoTEC plus system boiler - DHW control?

[Ric2013]

Hi there,

Boiler question, but nothing that contravenes gas regs.

To get to the point, the Vaillant EcoTEC Plus seems to have two knobs. One has a tap symbol, the other has a radiator symbol. Even the system boiler version of this boiler has two knobs.

What I cannot make out is what purpose the DHW control knob has on a system boiler. And I'm still confused having read the manual, as the boiler manual isn't very clear (especially to me who isn't even sure what the time is today).

Does the boiler fire at a higher flow temperature when it knows it is heating hot water? This would be the logical way of being able to set a proper condensing temperature when the cylinder is satisfied, but I can't see anything in the wiring diagram that would suggest the boiler knows whether it is heating a cylinder or radiators.

I have told the customer that while I don't think the DHW control knob does anything on her system boiler variant, I'm really not sure.

Hoping someone with more Vaillant experience will be able to enlighten me....

 

[king of pipes]

It doesn't do anything on a heat only boiler Ric the boiler modulates up and down due to heating demand usually by using ntc thermistors in the flow and return pipework in the boiler they work on resistance measured on the ohmes scale and reduce or increase the resistance at different temperatures when heat is past over them in turn controling the boilers modulation process , best practice to achieve satisfactory hot water demand is set the boiler temperature to 65° c this temperature is hot enough to switch the cylinder thermostat off at 60° c but still achieving a good supply temperature to the radiators if that makes sense . Kop

 

[Ric2013]

Yes, it does make sense. Anything less than 65°C would really struggle to heat the cylinder to the required temperature, but any more and you risk not having the boiler condense the rest of the time.

So, in the age of smart controls and weather comp, has any boiler manufacturer actually made a boiler that will run at one temperature for space heating, and then ramp up to a higher setting when heating a cylinder? This would seem desirable, or am I missing something fundemental?

 

[king of pipes]

Yes but they use a Combi and connect it to a 100 litre unvented vessel alpha are the ones who spring to mind . Kop

 

[Brambles]

The normal way of configuring weather compensation for a single channel system boiler is to use a relay on the weather compensation connection. When CH calls for heat, the relay remains closed, so weather compensation operates. When DHW is called the relay opens so weather compensation is ignored and a high flow temperature is delivered.

The relay is activated (opened) by the micro switch on the DHW control valve.

 

[garygvl]

Yes, it does make sense. Anything less than 65°C would really struggle to heat the cylinder to the required temperature, but any more and you risk not having the boiler condense the rest of the time.

So, in the age of smart controls and weather comp, has any boiler manufacturer actually made a boiler that will run at one temperature for space heating, and then ramp up to a higher setting when heating a cylinder? This would seem desirable, or am I missing something fundemental?

Ideal logic heat five words

 

[Scott_D]

Yes, it does make sense. Anything less than 65°C would really struggle to heat the cylinder to the required temperature, but any more and you risk not having the boiler condense the rest of the time.

So, in the age of smart controls and weather comp, has any boiler manufacturer actually made a boiler that will run at one temperature for space heating, and then ramp up to a higher setting when heating a cylinder? This would seem desirable, or am I missing something fundemental?

Ideal boilers do this

 

[EvilDrPorkChop]

So, in the age of smart controls and weather comp, has any boiler manufacturer actually made a boiler that will run at one temperature for space heating, and then ramp up to a higher setting when heating a cylinder? This would seem desirable, or am I missing something fundemental?

Actually Vaillant was one of the first to do this I believe, they were well ahead of the game 10+years ago. Other manufactures are only just starting to do this, where the germans have been doing this a while. The issue is here that you aren't using the Vaillant wiring centre, cylinder probe and controls.

If you use their own controls it'll allow you to do precisely as you say. You'll get HW priority where you can use the boiler front to select the temperature of the water, it'll have a higher flow temperature for quicker HW recovery, and you can select the output of the KW of the boiler to match the cylinder coil. It'll then allow you to run a lower flow temperature for your central heating circuit, whilst the controller modulates the temperature through the eBus system.

The issue is whoever fitted the boiler originally has just used the S/L to get the boiler to come on or off therefore it cannot differentiate between a HW demand or CH demand.

 

[Ric2013]

Actually Vaillant was one of the first to do this I believe, they were well ahead of the game 10+years ago. Other manufactures are only just starting to do this, where the germans have been doing this a while. The issue is here that you aren't using the Vaillant wiring centre, cylinder probe and controls.

If you use their own controls it'll allow you to do precisely as you say. You'll get HW priority where you can use the boiler front to select the temperature of the water, it'll have a higher flow temperature for quicker HW recovery, and you can select the output of the KW of the boiler to match the cylinder coil. It'll then allow you to run a lower flow temperature for your central heating circuit, whilst the controller modulates the temperature through the eBus system.

The issue is whoever fitted the boiler originally has just used the S/L to get the boiler to come on or off therefore it cannot differentiate between a HW demand or CH demand.

That's good to know. I was puzzling at the IOM for some time trying to work out if there was the presumption you'd use their own controls and that that knob would then serve a purpose.

 

[EvilDrPorkChop]

That's good to know. I was puzzling at the IOM for some time trying to work out if there was the presumption you'd use their own controls and that that knob would then serve a purpose.

Vaillants instructions aren't great at times, especially when it comes to wiring! The controls instructions aren't much better either.

 

[Ric2013]

Vaillants instructions aren't great at times, especially when it comes to wiring! The controls instructions aren't much better either.

Yes. I assume it's the VR 65 control center (sic.), but it would be good if the IOM said what you explained above. Can't help thinking that had I been an RGI, I'd have used a simple switched live, whereas, having read your explanation, I wouldn't.

 

[EvilDrPorkChop]

Yes. I assume it's the VR 65 control center (sic.), but it would be good if the IOM said what you explained above. Can't help thinking that had I been an RGI, I'd have used a simple switched live, whereas, having read your explanation, I wouldn't.

I believe the VR65 has now been replaced by the VR66, again Vaillant have never really stated this anywhere!

 

[Ric2013]

No dount. I was just quoting the IOM which refers to the aforesaid control centre without explaining why you'd want to use it.

 

[king of pipes]

Valliant controls are ok if you're good with tech where they fall down is in their installer and user instructions far far to complicated for the average person to use, installers don't understand them electricians don't know how to wire them, Their boilers are as good as any other of the top 5, I myself sometimes install them 9 times out of ten I would use Honeywell controls or a form of smart control why ! Only reason is because they are easy to install , to set up and are user friendly even my Senior clients can use them , install a VR control they would struggle and would result in nuisance call backs for me, I did fit one once to a combi in a beauticians lost count how many times I went back nightmare, I would want to do the Valliant training before ever trying them again.