Vaillant system misbehaving

[Airmiles]

Hi All,

I've viewed the forum a lot recently but this is my first actual posting. I'm hoping someone can shed some light on this, though I can't find anything similar posted previously.

We have a brand new Vaillant-based system which was recently installed as part of a house refurbishment, but which we now realise is not working as it should. I suspect there may be more than one problem interacting, just to make life more difficult.

For various reasons we have long lost faith in the builders responsible, but I'd like to do some basic checks before going to a 3rd party picked at random from Vaillant's website, particularly as it doesn't seem a common set of symptoms. I can't touch anything myself and still hold the builders accountable.

the system is
Vaillant ecoTec Plus 630 boiler
VR65 Control centre
VRC470 weather compensator
Thermastor horizontal unvented cylinder.

It's plumbed as (I think) a Y, that is to say a single flow split in two with two, 2-way valves for CH and HW. The HW cyclinder has a variable thermostat which is wired into the VR65. We have not used the HW temp sensor supplied with the VR65.

HW is fine, maybe not as hot as I'd like but the tank thermostat is 70 max so what we get seems in line with that. The main symptom is that the CH only comes on with the HW, and at HW flow temperatures (which is to say 70+; scaldingly unsafe for my toddler....)

Note: the tank also has immersion heaters. The switch for these is unlabelled for on/off.....

The secondary issue is that whilst the VRC470 is internally "correct", and it and boiler are clearly "talking" on the eBus (more details below), the boiler does not acknowledge the VRC470 thermostat.

In more detail:

Boiler is at factory defaults throughout. I've varied a lot on the VRC470 but manually set it back to at or close to factory settings.

Boiler D.090 "Digital Controller Status" is "1.Recognised"

The VRC470's display of internal and outside temperatures are correct (or at least "reasonable"..). Boiler D.047 shows this same outside temperature.

With VRC470 set to "modulating", "Flow Temp target" adjusts appropriately for adjustments to both desired temperature and heating curve. The boiler diagnostics (D.005 and D.009) both reflect this FTT

However.. no amount of adjustment to Desired temperature or Heating timed programs, between "Modulating" and "thermostat" or indeed HW on/off, can get the boiler's thermostat status to shift from D.008 = "0. Open" (no heat requirement), even with target flow temps over 50 deg C. [summer offset is 0K, heat curve 2.25]

When the HW (and rads...) are on, the 470 shows Heat Generator Status as "DHW".

Finally, whilst HW is on and most rads open and warming up, Flow (D.040) is at 63 and return (D.041) at 45.

So I suspect it's some variation of:

1. Obscure Electronic setting, incompatibility, or outright fault preventing the CH thermostat coming on
2. Plumbing, mechanical, or wiring fault in the CH and/or DHW valves (possibly valve DHW and CH wiring in the VR65 inverted and immersions are providing HW ??)

(2) seems solvable in both the detecting and fixing sense, but does it sound like a reasonable diagnosis?

1. is just.. weird. the controller and boiler are clearly talking on the bus, and the controller clearly tells the correct temperature. VR65 was specifically recommended by Vaillant tech support for this install.

Many thanks
Miles

 

[oldbuffer]

I've got a similar set up, and it took quite a while to get it right.

The key I've found is making sure the programmer does not call for HW and CH at the same time.

With HW only, the boiler will run a flow temperature of up to around 75, which is fine for heating the water up to about 65.

The CH comes on after the HW, and with a heat curve of 2.0 (or thereabouts) normally runs at a flow temperature of 50 to 60, and runs 20 radiators perfectly well.

There is a parameter setting which I had to change in the installers set on the boiler, can't remember which one but I think it had something to do with hot water priority. If its any help I could look it up and let you know.

 

[Airmiles]

Ah, thanks for replying oldbuffer. Was this a parameter setting, or a physical one? There are a couple of shunts in the boiler and another one in the VR65 that are not well-explained in the instructions.

I did miss out that rather vital piece of information - I had exactly the same thought two days ago, and re-set the timings so DHW and CH didn't overlap.. with no change in symptoms. It was at that point I realised it might not be "pilot error" after all.

So to clarify, when the timing is DHW-only, the rads are coming on at T=scorchio, which is why I think something is up with the valves, and when the timing is CH-only, there is no CH and D.008 is not calling for heating load.

D.008 could be a) something up with the electronics, or b) due to the valves being reversed, and/or c) incorrect shunt settings in either/both boiler and VR65. It's throwing fault code F.78, the wording of which implies it expects the VR65 to be shunted if a cylinder temp sensor is not installed....[/i]

 

[fishpond]

Hi

Your installation seems pretty straight forward. It sounds like it just needs to be configured and programmed properly, since based on your write up I don't think you fully understand the setting parameters and their meanings.

The vrc470 is a great bit of kit and works very well once set up correctly.

The only additional thing I'd suggest is that you use the vr10 sensor with your cylinder... The existing cylinder stat can be wired up to act as a safely, but the vr10 should be used for maximum functionality.

...and then you need to have it configured correctly!

 

[Agile]

As far as I can read between the lines, your unvented cylinder is currently likely to be classed as unsafe.

You do not seem to have either a spring return two port valve on the heating coil of the cylinder.

OR

You do not have the Vaillant heat sensor fitted to the cylinder.

Clearly from the information that you have supplied the unvented was not installed by anyone who was appropriately qualified.

Presumably the cylinder was not notified to Building Control ( BC ) either!

Was the boiler Benchmark Certificate completed? Was that notified to BC ?

Tony

 

[fishpond]

As far as I can read between the lines, your unvented cylinder is currently likely to be classed as unsafe.

You do not seem to have either a spring return two port valve on the heating coil of the cylinder.

OR

You do not have the Vaillant heat sensor fitted to the cylinder.

Clearly from the information that you have supplied the unvented was not installed by anyone who was appropriately qualified.

Presumably the cylinder was not notified to Building Control ( BC ) either!

Was the boiler Benchmark Certificate completed? Was that notified to BC ?

Tony

Tony

Not sure how you can make such sweeping accusations without even seeing the installation!

If you read the first post, he states that he has 2x 2 ports... And he says that he is not using the vr10.

Perhaps you should stick to reading what's there rather than trying to read between the lines...

 

[Agile]

He said that its plumbed as a "Y" which made me ( wrongly ) think that it would have a three port.

Even so there is nothing he has said than makes me feel confident that it has been correctly connected as an unvented should be to be safe.

I have no faith in "Builders" who install unventeds!

For anyone who does not know they can explode!

Tony

 

[Airmiles]

All,

This is now sorted, thanks.

It was in fact as simple as the valves being wired the wrong way round in the controller.. clouded by a couple of "features"with Vaillant diagnostic codes and controls.

So once the valves were wired the other way round we now have DHW at DHW temperature and CH at CH temperature. Modulating is working correctly, once DHW and CH are scheduled at separate times. As and when the weather gets colder we'll see how the heat curves go.

for anyone's future interest:

D.008 is redundant. It's D.016 that tells the truth about the heating demand.

F.078 seems unavoidable without a valllant cylinder.

In this install you seem limited to the cylinder open/close thermostat ONLY. using the Vaillant sensor in the NTC slot, either with or without the cylinder thermostat, results in no DHW.

Ultimately it was very simple problem which would have been quicker to solve without the distractionsarising from the difference between the reality of the vaillant setup rather than the mildly fictional manuals. Inaccurate and over-excited postings don't really help.


Also for reference, yes this system does have BC approval.

Thanks

Miles