Vaillant VRC700 - Temp Mod vs Thermost Temp Mod or None

[Ian Clarke]

Hi,

Can some one please explain the difference in plain english as struggling with manual for Activating Room Temp Mod.

None
Temp mod
Thermostat Temp mod

Installer said if set on thermostat its not a true weather compensator just an expensive thermostat, although I have set on thermostat.


Can someone explain if possible what the differences are between the 3 settings, and if not on thermostat how does it get the room to 20/21 if that's what set it too. Just thinking if on thermostat it is turning boiler off and on as you would expect but also read that weather compensation shouldn't do this but actually leave it on all the time firing lower, instead of 60c flow.

Thanks in advance

 

[ScottishGasMan]

Hi,

Can some one please explain the difference in plain english as struggling with manual for Activating Room Temp Mod.

None
Temp mod
Thermostat Temp mod

Installer said if set on thermostat its not a true weather compensator just an expensive thermostat, although I have set on thermostat.


Can someone explain if possible what the differences are between the 3 settings, and if not on thermostat how does it get the room to 20/21 if that's what set it too. Just thinking if on thermostat it is turning boiler off and on as you would expect but also read that weather compensation shouldn't do this but actually leave it on all the time firing lower, instead of 60c flow.

Thanks in advance

Temp Mod = weather compensation taking into account the current room temperature
Thermostat = STILL weather compensation taking into account the current room temperature BUT will also cut the heating off completely if it goes over temperature and bring it back on once the room temperature drops.

On a perfectly balanced system in a well insulated house then Temp mod would be good, but Thermostat function still runs the WC exactly the same, but more suited to retrofit where rads/ventilation/heatloss may not all be perfectly balances so allows the system to cut off for a while if needed.

On either setting its dependant on the Curve being set right, as to high and regardless of room temperature the flow temperature will to too warm and overshoot the desired heating temperature in the house.

To prove to yourself right and installer wrong. Set it to thermostat, then turn the heat curve all the way down, youll see the flow temp stays very low as its still in Weather Compensation mode.

 

[Ian Clarke]

Can I ask do you know why it has a none setting and that’s default from factory, I would have thought it would only have the two settings temp mod or thermostat if they the ones to always use.. think that’s what’s confusing me.. vaillant also said curve normally 2.1 to 2.8 but it’s actually moving itself down when started on 2.0 it’s now down to 1.7

 

[ScottishGasMan]

Because these controllers are for a massive range of applications and appliances from your single heating zone domestic, to large cascade commercial systems with heat pumps/solar/ventilation control all in one, so there are a number of settings that you wouldn't use in a house and unfortunately what makes them so complicated to set up.

If the heat curve is still on auto adapt then it must be reaching room temperature and/or overshooting so it will automatically lower it to suit, although the auto processes are never 100% reliable, but if at 1.7 your still getting to the set temperature then thats a good thing

 

[Ian Clarke]

Thanks very much for your quick replies, that makes sense, it’s lowered to 1.7 and still overshooting at moment, room getting to 21.5 when called to be 20.5, although this better than first day when curve had been left on 1.2 and it never got to 20.5 .

Guess it’s the fine tuning now, when I spent 45mins on phone yesterday to vaillant all he wanted to do was ensure a 15 difference between d40 and d41 on first fire up and had me increase d0 to 20 to get that.

 

[ScottishGasMan]

Yea, its a case of either leaving it to it, or manualy trying different values for the curve, I tend to leave mine a tad low so that it often wont get to it, but will get pretty close, that way the boiler pump keeps circulating and the rest of the rooms keep being fed with some heat (its rare that all the rooms will loose heat at the same rate so it can help a little at keeping them balanced rather than the lot going off and a room loosing temperature quicker than the hall ends up cold)

 

[Ian Clarke]

Thank you think be better at Lowe then, do you leave auto on though, or turn that off and say set to 1.5 and see how it goes, do you agree with the vaillant guy just trying to get d40/41 15 difference, he basically said it was always on as the system small so water returning too hot. Asked me some settings, did some calculations, said it’s using x per min litres and set d0 to 20 and then we do get exactly 15 back, although he even said with all rads it should be d0 - 12

 

[ScottishGasMan]

the temperature of the return water will be massively affected by the efficiency of the radiators. ie you could have small single panel rads, or massive triple panel ones, they may be balanced or restricted, or open full bore, so knowing the temp difference between the flow and return wont yeild any useful info without a lot of other info on the system, although when systems heating up running full tilt, I wouldnt want D40/41 to be any further apart than 20,

Biggest thing is having weather comp on system at all, and having curve set as low as can be comfortably heated, the output of boiler being 12 or 20 would be saving a fraction of a fraction of a percent of gas, boiler will modulate the output once the flow temperature has reached what the weather comp wants anyway. But again, if you want to try it, lower D0 to what you want and see how it goes, you could set it at 12kw and thats fine, but when its -2 outside next it may not be enough to keep up with the heat loss, so generally better to be a little bit over on D0 than under.

 

[Ian Clarke]

Thank you for all your help and advice. As said trying to get this setup right, isn’t easy, hoped installer knew it, but unfortunately didn’t, in fact told me didn’t rate wc units at all and at moment it’s been using more gas per day than before having it, I appreciate weather too and hopefully will see better savings when it gets milder as assume that’s when they come more into there own, as then the curve better.

I’ll leave d0 alone, it was on fire up it was only getting around 11 difference and he wanted that to be 15 and then modulate down to 7 to 10 difference. I had actually phoned vaillant to ask them what they recommended the heat curve to be set too.

Detached bungalow, 2 bed in Derbyshire, 1990 built so cavity etc and they said we say 2.1 to 2.8 and might be using so much gas as curve set too LOW. To me that didn’t make sense as thought lower more economical not worse. Told her it was moving downwards automatically when set at 2

 

[Ian Clarke]

Should the 831 boiler know it’s got the vrc700 connected, it is via ebus and 3 and 4 closed but according to boiler manual d47 is Outdoor temp (with weather compensating vaillant controller only) should show actual degrees outside, yet vrc700 showing 7 degrees, d47 reads 999 ?

Just wondering if installer wired something wrong, mark one 2011 boiler

 

[rbranco]

Should the 831 boiler know it’s got the vrc700 connected, it is via ebus and 3 and 4 closed but according to boiler manual d47 is Outdoor temp (with weather compensating vaillant controller only) should show actual degrees outside, yet vrc700 showing 7 degrees, d47 reads 999 ?

Just wondering if installer wired something wrong, mark one 2011 boiler

If you have a wired VRC then OT sensor connects to the boiler, if its wireless VRC then it communicates to the VRC directly. On my 418 it's wireless and d47 is 999 but it shows correct value on the VRC controller.

Check d05, this is the requested target flow temp by ebus, it should go up/down and (on my 720f) it shows target flow temp on controller as well.

Remember that VRC tells boiler what to do, if the VRC is disconnected the boiler should end up being on 247, so essentially the controller is telling boiler to halt and lower target temp from what is set on the panel.

 

[Johntheo5]

Thanks very much for your quick replies, that makes sense, it’s lowered to 1.7 and still overshooting at moment, room getting to 21.5 when called to be 20.5, although this better than first day when curve had been left on 1.2 and it never got to 20.5 .

Guess it’s the fine tuning now, when I spent 45mins on phone yesterday to vaillant all he wanted to do was ensure a 15 difference between d40 and d41 on first fire up and had me increase d0 to 20 to get that.

Wonder was he suggesting 15C dT because Vaillant fireup (or used to) at 65% output irrespective of range rating like a lot of other makes but then hold this firing rate for 60 secs before releasing the controls to modulation, this requires a fairly high flow rate to avoid burner cut out at SP+5C and repeated cycling then unless the anti cycle time is set fairly long.

 

[Harry Bloomfield]

vaillant also said curve normally 2.1 to 2.8 but it’s actually moving itself down when started on 2.0 it’s now down to 1.7

Mine does that too, you set an initial value, it then fine tunes the value as it 'learns'.