Vaillant discontinue VRC 430 before replacement is in stock?

[Mboursnell]

So "modulating" and "thermostat" both use the outside temperature. What exactly is the difference then? Are you saying that "thermostat" only uses the OT when the desired room temp hasn't been reached, but that "modulating" uses it all the time?

That doesn't make a huge amount of sense to me. I think I have missed something.

 

[ALEC1]

modulating also looks at the room temperature and adjusts the flow temperature within parameters, thermatat shuts down the whole system when the target room temp is reachesd None the boiler follows the heat curve..

 

[David937]

As I see it, in 'Thermostat' mode my 430 looks at both the room and outdoor temperature to decide on what flow temperature to use and switches off when the room temperature is reached, the flow temperature also ramps down as the room approaches it's target temperature. It will remain off until the room drops 0.5ºc below the target temperature. I know it definitely looks at the room temperature as once some windows were left open when it was around 11ºc outside which made the house very cool, when the heating was fired up it used quite a high flow temperature to quickly bring the house up to temperature. Ordinarily, at that sort of outside temperature when it is just bringing the house up from the setback temperature, the flow temperature is a lot lower.

In modulating mode, it attempts to keep the boiler running at a constant low flow temperature to maintain the target temperature, it will only switch off if the room temperature overshoots by 3ºc. I did try modulating but the house would overheat since my boiler can only modulate down to 12kw and cannot maintain a flow temperature much lower than 50ºc without cycling.

This is all based on what I have tried and observed in the first few months of owning a VRC430. It is now left on Thermostat with a set time programme and is rarely ever touched

HTH

 

[slup]

The 430 and the 470 must differ then - I've got mine set to modulating mode and don't get any overshoot at all. As the temperature gets close to the set point, the boiler output gradually ramps down and eventually shuts off.

 

[Mboursnell]

Maybe the different behaviours are due to different heat curves? Perhaps with a high heat curve you get more overshoot of the desired temperature.

Does anyone know what an "Adaptive Heat Curve" is?

 

[David937]

The 430 and the 470 must differ then - I've got mine set to modulating mode and don't get any overshoot at all. As the temperature gets close to the set point, the boiler output gradually ramps down and eventually shuts off.

Yes but mine can't really ramp down very much, it only modulates down to 12kw so the flow temperature begins to overshoot and hence causes the room temperature to overshoot!

 

[ALEC1]

I think the post above says it all..

I only install and commison boilers, and Vaillant, in common with all manufacturers dont give much away. I think modulation operates a degree or two (room temp) either side if the curve.. so the curve has to be broadly right. This Vaillant only, not other manufacturers.


I dont think modulation turns the heating off, just lowers the flow temp..


an adaptive heat curve is one that learns over time the charateristics of the house AND heat emitters..so curve setting becomes less critical..

 

[ALEC1]

what boilers are these on?

 

[slup]

Mine's an 831 - it definitely fully shuts down. Heat curve is set to 2.1.

 

[slup]

Actually, I've got mine set to Thermostatic mode, not modulating.

I think they both do the same (in terms of the modulation), but it's the thermostatic mode that actually fully shuts the boiler down as well.

 

[ALEC1]

I wold expect shut down in thermostat mode, not modulating control..

the three options are the same for both the 430 and the 470.

 

[slup]

The confusion isn't helped by the manual. Looks like they renamed the menu option on the controller but didn't update the manual:-

None:

Thermostatic control:
The built-in temperature sensor measures the current room temperature in the reference room. This value is compared with the target room temperature and, if there is a difference, results in adjustment of the heating flow temperature by means of the so-called "Effective target room temperature".
Effective room set target temp. = set room target
temp. + (set room set temp. - measured room set temp.) The effective target room temperature is then used for controlling instead of the set target room temperature.

Thermostat:
Works in the same way as thermostatic control, however the heating circuit is also switched off when the meas- ured target room temperature is +3 °C greater than the set target room temperature.
When the room temperature falls 2 °C below the set tar- get room temperature again, the heating circuit is switched on again.
The use of room thermostat control, in combination with careful selection of the heating curve, leads to optimum control of the heating installation.

On the actual controller, the order of the options is 'None, Modulating, Thermostat' - so I reckon 'Thermostatic Control' above is 'Modulating'.

This also means that the 'Thermostat' option does 'Modulate' as well!

 

[ALEC1]

That too is also correct..

These vaillant controllers are good stuff, but Vaillant don't help themselves with their translations, or english for tha matter

 

[David937]

The instructions are truly awful which is why I just tried each option and worked out how it operates and then chose what is best for me.

 

[slup]

We've both ended up using the same setting, but I don't have any overshoot. Is it worth tinkering with your heat curve?