Vaillant 624 system boiler with Unistor and 2 zones CH/UFH - CH zone help needed

[acideraser]

I believe I looked through all posts here regarding to Vaillant system boiler with CH/UFH 2 zones setup but could not find a response though all the info was very helpful.


It is a new system installed by in the extension which consists of:
- Vaillant ecotech 624 system boiler v.6.08
- Unistor cylinder
- VR 61/4 Control centre v.4.18
- VRC 470 weather compensator (and thermostat used for UFH zone downstairs) v.4.20
- VR 81/2 thermostat for CH upstairs v.2.02
- DHW circulation pump

CH is zone 1, controlled by VR 81/2 upstairs
UFH is zone 2, controlled by VRC 470 in downstairs

Settings for CH (zone 1):
Minimum Temp: 40 Deg C
Maximum Temp: 70 Deg C
Auto Off mode: Eco
Room temp mod: Thermostat
Summer mode offset: 1K
Heating curve: 1,20

I understand from the plumber that system was installed using Hydraulic drawing 4:
http://www.manualslib.com/manual/538755/Vaillant-Vr-61.html?page=10#manual

I believe this is in line with what other guys with similar setup mentioned on this forum

Photos of the pipework if it helps:




However it seems there is no such diagram in the manual which came with my VRC470 so he selected system diagram 3 in VRC470.
The issue I have is that when diagram 3 is selected CH (zone1) does not come on when temp upstairs falls irrespectively of time program or if always on. UFH (zone2) works fine at the same time.

Here is the diagram 3 from my manual:


I noticed that when diagram 3 selected motorised valve on DHW circuit is constantly open and it seem to charge cylinder irrespectively of time program or even when DHW is set on off. Little tap icon keeps flashing on the boiler screen as well:


r


The only way to get zone 1 heating on is to either manually open motorised valve or select system diagram 1 in VRC 470 installer menu. In this case both zones UFH and CH work perfectly, heating comes on when thermostat temp drops below desired level so all good except sometimes (once a week or so) it can suddenly ran out of hot water and boiler does not respond cylinder boost in this mode, little tap icon does not appear on boiler screen either. Again the only way I found to get water is to manually open motorised valve when Boiler is on for CH or to set it to back to system diagram 1.

These are photos of two variants of diagrams 1 which I believe correspond to my set-up more or less.




Circulation pumps seem to be working fine in both cases.

Appreciate any advice/suggestion please, will have to speak to Vaillant support as well.

Cheers

 

[acideraser]

bump

 

[simond]

Where does it say in G3 that you can put an unvented discharge into an open PVC pipe?

 

[acideraser]

Hi Simon, thank for your response but not sure I can answer your question as I am not familiar with G3 though I do not see how this affects issues with heating and hot water mentioned in this post.

 

[simond]

In your Oct 2015 posts you said this set up was working fine with respect to the zoning.

Perhaps the controls were suitably unfathomable that you didn't realise then? The condense trap shows this system has been running for at least 6 months.

We started fitting Vaillant weather comp in 2004 with the first ecoTEC and found software errors, which Vaillant did rectify after getting Germany involved. Since then we have persevered with various VRC controllers but some years ago I realised that if the customer can't understand it, it must be poorly designed and not fit for purpose. Vaillant controls have always been designed by a programmer for a programmer.

The diagrams we've got show a VR40 expansion module being needed for the bronze pump, but your diagrams don't. As far as I can remember (we don't actively install Vaillant products now) only the 37Kw domestic models come with a VR40 onboard the PCB.

I think Group Service technical are where you need to go; I pity anyone else in your family having to work out how to control this on a day to day basis. I think Steve Jobs had the right idea; if it isn't almost immediately obvious, it is poor design. If Vaillant designed the wheel, it would have four button presses, and one long press, to get it turning.

If you want a clever control system, rip it all out and fit Evohome. It is a marvel in human factors design, and will make your boiler system more efficient.

 

[acideraser]

Thanks for pointing out to possible need of VR40. I just checked manual it indeed says that VR40 (multifunctional module) needed to connect circulation pump to the system and it is on board of PCB of 637/837 models only.

This diagram also shows circulation pump connected via VR40 <a href='http://www.manualslib.com/manual/538755/Vaillant-Vr-61.html?page=10'>EW 1200 i on manualslib.com</a>

What I don't understand though is that circulation pump (bronze) is working fine and when it is supposed to, it's the cylinder charging I have issues with... It just seems that DHW flow temp is not what I set in controls (45 Deg) but whatever is flow temp of CH, hence when it is cold outside I have hot water without issues but when it gets warmer and weather compensator reduces CH flow temp to below 20 or 30 deg C flow from the hot tap is not hot...

Just one more question - Do I need a separate cylinder charging pump to connect via VR40 or there is one inside the boiler?

cheers

 

[acideraser]

Here is an update:
- There is VR40 next to PCB in the boiler and Circulation pump connected via VR40, aux.relay 1 (D27)
- Vaillant confirmed that System diagram 3 is correct diagram for this set-up
- When diagram 3 is selected, there are no issued with DHW but motor valve to cylinder stays open all the time and LIve monitor on the boiler shows "S.20 - DHW demand".
- CH does not come on irrespectively of room temperature or time programs

I guess that constant DHW demand prevents central heating from switching on because Hot water has a priority but why would there be constant DHW demand even when water not used at all?

 

[jeff the gasman]

Reduce the cylinder temperature in the menu and make sure the boiler stat is on maximum.
Sounds like cylinder is not achieving set point.

 

[acideraser]

thanks Jeff, I've reduced DHW temperature but it didn't help.
Still shows DHW demand on live monitor but boiler is not firing, just motor valve open and sound like pump is running...

One thing which I considered not important and didn't mention before but after your post mentioning cylinder not achieving the set point I suspect this may be important: VRC470 does not show actual Cylinder temperature at all, this is how it looks like on this photo. in fact it has been like this from the start. Could this be the reason?

Thank you

 

[Baz1312]

Hi, I see you mentioning trying to set the cylinder temperature via the boiler or vrc470. To do this you have to have a vr10 thermistor installed in the cylinder and connected to your control center. I don't see that mentioned in your setup.

 

[Baz1312]

Sorry forgot to add, the VR10 sensor enables setting hot water temp via boiler or VRC 470, it also allows boiler flow temp to increase to max (default 75c) during a dhw demand, shutting other zones giving priority to cylinder allowing it to recover its heat as quickly as possible (max time 17.5 minutes.)
When the weather comp sets a low flow temp the result is a low flow temp through cylinder coil when (VR10 not installed) thus affecting the secondary water temperature (you mentioned no hot water when this happens).

 

[The831Bunny]

Hi, I see you mentioning trying to set the cylinder temperature via the boiler or vrc470. To do this you have to have a vr10 thermistor installed in the cylinder and connected to your control center. I don't see that mentioned in your setup.

The VR10 needs to be connected to the boiler if using a VR61. The VR10 only connects directly to a VR66. The cylinder temperature will then display in D.4 and on the VRC470.

 

[Baz1312]

Ah ok. Still remains that if a vr10 is not fitted the controls/boiler cannot monitor the cylinder temp.

 

[The831Bunny]

Correct. The VR10 IS the cylinder temperature monitor. Also D.70 on the boiler should be set to 0 (zero - factory setting) which is HW priority mode.

 

[acideraser]

Hi Guys, thanks for your input and my apologies for not being clear in the original post. I seem to have learned a bit more about this system since then. below is updated specs:

- Vaillant ecotech 624 system boiler v.6.08
- Unistor cylinder 210L
- VR 61/4 Control centre v.4.18
- VRC 470 weather compensator (used as thermostat used for UFH zone downstairs) v.4.20
- VR 81/2 thermostat for CH upstairs v.2.02
- DHW circulation pump connected to boiler via VR40 extension module
- VR 10 sensor in cylinder dry pocket connected directly to the boiler

CH is zone 1, controlled by VR 81/2 upstairs
UFH is zone 2, controlled by VRC 470 in downstairs

There is VR 10 NRC, it is connected directly to the boiler, however Current cylinder temperature is not shown on VRC 470.

To summarise - the issue is that boiler constantly showing DHW demand but not firing. Boiler display looks like

this

all the time except when it actually heating water during pre-set time periods or Cylinder boost mode, in this case boiler display looks like this (there is a little Tap pictogram blinking)

My guess is that Constant DHW demand is preventing central heating from switching on as DHW has a priority and what causes constant DHW demand. Could it be faulty VR 10?