Vaillant VRC 430f cycling issues - a solution?

[David937]

I emailed Vaillant technical and their reply was:

The VRC430f should be set to 'Thermostat' and mounted in the main living area. They did not explain what 'Modulating' is even though I asked quite nicely. Anyway, I'm not too fussed about it now as my system is running really smoothly now with the VRC430f set to Thermostat. It's only on for 2 hours in the evening and 2 hours in the morning (3 on weekends) at the moment.

I called Vaillant technical today as well and they confirmed that if the VRC430 was away from the boiler and used as a thermostat you should also set it as thermostat not modulating. They said modulating was for when you had no thermostat and it would use the outside temperature and the curve setting to set the temperature. So I presume you would keep altering the curve until it gives you an exceptable temperature.

They also said for me the curve should be set at 2.3.

Also I have set my minimum temperature to 50c and that seems to stop most of the cycling.

Glad you got it sorted I presume by no thermostat they mean the VRC430 is mounted on the boiler with the VR81 acting as the thermostat possibly.

 

[Gary27]

I emailed Vaillant technical and their reply was:

The VRC430f should be set to 'Thermostat' and mounted in the main living area. They did not explain what 'Modulating' is even though I asked quite nicely. Anyway, I'm not too fussed about it now as my system is running really smoothly now with the VRC430f set to Thermostat. It's only on for 2 hours in the evening and 2 hours in the morning (3 on weekends) at the moment.

I called Vaillant technical today as well and they confirmed that if the VRC430 was away from the boiler and used as a thermostat you should also set it as thermostat not modulating. They said modulating was for when you had no thermostat and it would use the outside temperature and the curve setting to set the temperature. So I presume you would keep altering the curve until it gives you an exceptable temperature.

They also said for me the curve should be set at 2.3.

Also I have set my minimum temperature to 50c and that seems to stop most of the cycling.

Glad you got it sorted I presume by no thermostat they mean the VRC430 is mounted on the boiler with the VR81 acting as the thermostat possibly.

I assumed that but they said it was if you did not have a thermostat.

 

[smokebox]

Gary
What information did you give Vaillant for them to suggest your heating curve number of 2.3?

smokebox

 

[Tipper]

I'm interested in that too as I have just upgraded to a 430f with my 937.

Is there some method involved in deciding which curve to use or is it just guesswork?

I'm curentluy running 2.0 and now it's got colder we're nice and cosy. Frankly it hasn't been much good up to now.

I assume the controller learns more about the heat demands of the building as time goes by. But would it be more economical on a lower curve?

 

[David937]

I'm interested in that too as I have just upgraded to a 430f with my 937.

Is there some method involved in deciding which curve to use or is it just guesswork?

I'm curentluy running 2.0 and now it's got colder we're nice and cosy. Frankly it hasn't been much good up to now.

I assume the controller learns more about the heat demands of the building as time goes by. But would it be more economical on a lower curve?

My VRC430f is set to 50ºc minimum flow temperature and a curve of 2.7, I did try 2.8 but found the house overheated, 2.7 works fine. The curve depends on the insulation of your house, our house is badly insulated apart from the extension so the curve of 2.7 was chosen based on 95% of the house, TRV's stop the temperature getting too high in the extension.

 

[Onetap]

In reality its not always so good. For example a force 9 gale greatly increases heat loss and draughts.

The other instance where simple weather control is inadequate is during warm-up. For example, if it is 10 degC outside, the weather compensation curve might determine that the heating flow should be, say, 55 degC. However, if the office heating has just started up after a weekend and it is 10 degC inside and outside, then you will want the flow temperature on maximum until the temperature is up to 21 degC. However, simple WC says you get 55 degC and that's what you get.

The mathematics of WC is set out here, the only article I know that explains this;

http://www.pmengineer.com/CDA/Archives/cdd55d5472298010VgnVCM100000f932a8c0

It is American, it is in imperial units and they call WC 'outdoor reset'.

I think Vaillant may have misinformed you about the thermostat and modulating settings. I understood the different methods of operation to be as explained in this paragraph;

Indoor temperature feedback may be provided through a simple on/off thermostat that temporarily prevents further heat input from the device the reset controller regulates (boiler, mixing valve, etc). It can also be provided by an interior temperature sensor that allows the reset control to automatically shift its reset line downward (to compensate for internal heat gain) or upward (to compensate for a higher than normal heat loss).

 

[anecdotal]

I am having the same issues. I have wall mounted VRC430 (actually sunk mine into the wall) and EcoTECH plus 831 combi and the manual is rubbish. I am doing up my house and have had this combination for about 1 year (last winter I could not seem to get enough heat out of it when it was -6 outside) - seems to keep circulating with no burners I have to keep going back to the boiler and seeing what the front panel thinks its doing (pressing the 'i' button)

These post make me laugh (or maybe that is cry). The endless tweaking and frustration of trying to get this system running is driving me mad. And google searches on this topic seems full of lucky Valliant owners wasting spare hours.

For me 'Modulation' seems to cause the device to come on when the 430 target temp is way above set room temp just because the time window allows it. Temperature of room seems ignored and 430 displays much higher temp than i needed it to get to.

Thermostat seem the best setting, but I find, some how, when the boiler cuts in because room temperature is below that programmed, it starts up fine, goes for a while and then switches of (for like 15mins - could be 'max pump blocking time') then starts up again.

I am currently trying heat curve of 2.3, min temp of 20 (reduced form 40), and thermostat - see how that goes.

I have been trying to balance rads to ensure I did not have some sort of bypass. I think when VF! reaches same tempt as target flow it does this. Also I moved outside sensor to shady North facing wall to stop early/lend of day sun artificially changing the curve ...and the initially the room temperature control is set to 'none' - which was a nice default!

In theory this system should be very flexible, but it's mental. You should just come in set the temperature and forget it. Half thinking of buying a basic Drayton type controller ...or maybe the PC software or v81 to help monitor

 

[BarryCambs]

I think this relies on air circulating through the unit to detect the temp, so not sure it's going to work if sunk into the wall??

I have had a VRC400 and VRC430 both on a 831 boiler, and haven't had any issues after the initial set up. The system seems to work well for me. It's set to thermostat control, minimum temp of 40 and I think a curve of 2, but it's been set and forget for 3 winters.

 

[smokebox]

Moderator can you help me!
I hit ignore for Barrycamb in error when i wanted to quote him! and reply.
Can you restore him for me please! ASAP

Smokebox

 

[smokebox]

Barry camb

I agree about burying in the wall seems very counterintuitive for an air readingg thermomometer and stat. There will be hopeless lags in time response and relevance of timely information.

I note the instructions are pretty clear about surface mounting!

smokebox

 

[David937]

Moderator can you help me!
I hit ignore for Barrycamb in error when i wanted to quote him! and reply.
Can you restore him for me please! ASAP

Smokebox

Go to your settings and you can edit your ignore list.

 

[Onetap]

However, Aufschaltung (without the hyphon) translates to "activation" or "forward control" - I can't find a translator to get anything like "Modulating"...

'Feed forward control' is a control technique that is used in weather compensation controls.

The description on Pg.36 .....

"Forward 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 results in
a difference in an adjustment of the heating supply temperature."

Seems to describe a simple cascade control, that is;

1) a control loop compares the space temperature with the space temperature set point and , depending on the PID values, gives an output signal (0 to 100%) which rescales the hot water flow temperature up or down.

2) a second control loop uses the flow temperature from 1 above as its set-point (hence cascade, the output of one loop being the set-point input to the next) and compares this with the actual water flow temperature. This loop gives an output signal (0 to 100%, depending on its PID settings) which determines the modulating burner output or the mixing valve opening (0 to 100%).

Note that the outside temperature isn't used in this cascade control.

Feed Forward Control is a further elaboration of this in which, for weather compensation, a change in the outside air temperature is also used to rescale the output signal of loop 1 above. It is called feed forward because it anticipates a forthcoming increase in the heating demand on an outside temperature drop and increases the water flow temperature to accomodate this. And vice versa, of course.

Simple weather compensation simply sets the water flow temperature according to the instantaneous outside air temperature and doesn't consider the space temperature or any changes in the outside air temperature. This has some obvious inadequacies, but it is/was used on some domestic WC systems.

Sorry if that sounds complicated but if you've dealt with control systems it may make some sense. I suspect Vaillant don't want to give out detailed information on how it all works.

PS Editted to try to better explain this.

 

[David937]

I'm sure I read something very very similar in CIBSE Guide 'H'

 

[smokebox]

However, Aufschaltung (without the hyphon) translates to "activation" or "forward control" - I can't find a translator to get anything like "Modulating"...

'Feed forward control' is a control technique that is used in weather compensation controls.

The description on Pg.36 .....

"Forward 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 results in
a difference in an adjustment of the heating supply temperature."

Seems to describe a simple cascade control, that is;

1) a control loop compares the space temperature with the space temperature set point and , depending on the PID values, gives an output signal (0 to 100%) which rescales the hot water flow temperature up or down.

2) a second control loop uses the flow temperature from 1 above as its set-point (hence cascade) and compares this with the actual water flow temperature. This loop gives an output signal (0 to 100%, depending on its PID settings) which determines the modulating burner output or the mixing valve opening (0 to 100%) .

Feed Forward Control is a further elaboration of this in which a change in the outside air temperature is also used to rescale the output signal of loop 1 above. It is called feed forward because it anticipates a forthcoming increase in the heating demand on an outside temperature drop and increases the water flow temperature to accomodate this. And vice versa, of course.

Sorry if that sounds complicated but if you've dealt with control systems it may make some sense. I suspect Vaillant don't want to give out detailed information on how it all works.

Yes onetap - I reckon it his highly likely Vaillant has an anticipatory computed algorithm for impendind change in heat demand. They maw well be a bit secretive about this id detail!

smokebox

 

[anecdotal]

I think this relies on air circulating through the unit to detect the temp, so not sure it's going to work if sunk into the wall??

I have had a VRC400 and VRC430 both on a 831 boiler, and haven't had any issues after the initial set up. The system seems to work well for me. It's set to thermostat control, minimum temp of 40 and I think a curve of 2, but it's been set and forget for 3 winters.

I agree it may not be quite so good, but it looks much better and actually only suffers a little lag in true readings. Even so, the whole modulating/thermostat issue is unclear. And why does the system cut out (for ~15 mins) when it should still be in heat mode (temperature not reached on thermostat)