Vaillant ecotec plus cycling on HW only demand

[Agile]

Seeing so many over speced 400 series boilers, I have often wondered if it is possible to downrate the gas side to produce a lower output boiler.

On most models there is part of the inlet gas ways which differs on the various power outputs.

But I have never seen this suggested on any forum.

Perhaps I should investigate this and offer it to those unfortunates who have fitted over sized boilers?

 

[gaswizzard]

Seeing so many over speced 400 series boilers, I have often wondered if it is possible to downrate the gas side to produce a lower output boiler.

On most models there is part of the inlet gas ways which differs on the various power outputs.

But I have never seen this suggested on any forum.

Perhaps I should investigate this and offer it to those unfortunates who have fitted over sized boilers?

Don't waste your time , gas valve has no bearing regards input rate.

 

[scoobydo123]

Also yes it is oversized for the house it is in, but if I did need 28kw or even worse 38kw of heating load then it would still be the same outcome on the hot water side assuming that it is a software issue and not an installation/ fault.

I really wish I had access to another one to see if it behaves the same.


Gaswizard can you confirm if the ones that you have been to ALL exhibit this behaviour i.e. D0 ignored on EACH fire regardless of D40 D41 for 50 seconds per fire.

Really appreciate all the feedback and time taken.

 

[Agile]

I thought that the 50 sec was only on the FIRST fire of a sequence!

Your own test results also support that !

You have still not told me what you feel is wrong with how yours operates!

It gives a long fire to bring the cylinder up to temperature ( based on your d41 setting ). Then a few short fires.

You will get some interestingly different results if you increase the flow temp to 75 C.

Tony



PS The gas valve itself is not directly involved in the power setting of the various boilers. I never suggested that it was!

 

[gaswizzard]

On most models there is part of the inlet gas ways which differs on the various power outputs.

Which 'part' are you referring too?

 

[UpgradeME]

I thought that the 50 sec was only on the FIRST fire of a sequence!

Your own test results also support that !

I'm not so sure they do Tony? I don't think the OP has given us enough information (yet)..

As I mention a few pages ago, on my own 418 there is no 50 second firing at any kw. It just modulates as needed from startup (my tests were from 'cold' and the boiler was previously off, water temp was around 40C). It's by no means perfect as on low flow temps it struggles so there may be a 'lower limit' to it's startup kW (for emmissions reasons) but it's not set to 50 seconds like other posters have mentioned.

Googling around it looks like there are variations of system PCB's out there for the 400 series, however they all appear to have the same PN! I've seen various differences in components on board but have no idea if the actual software/logic is different. The VR65/VR10/VRT392 also add more advanced logic into the equation on my system. I've read lots of posts on here (and other sites) regarding this 'problem' but yet to find the root cause or a solution. My system is not unique either as there's posters on here that have also confirmed there system starts in the same way as mine. (Remember, people will rarely come on sites like these when there system is running perfectly well!)

With regards to the OP's problem, although his system startup behaviour may be exacerbating it, I agree with you and others that it sounds like the OP may also have a heat transfer / flow restriction.

On most models there is part of the inlet gas ways which differs on the various power outputs.

Which 'part' are you referring too?

Here's a nice diagram of parts to help!

 

[Agile]

I have not yet been convinced that there is really any problem with the OP's boiler operation.

The ebus controls take over the boiler operation and cannot be compared with the operation without external controls.

The part I have in mind is shown on that diagram but to be sure I would need to check the listing. Do you have a link to the whole document? Could be ein drossel klappe.

I would not mention it here anyway as I dont encourage encourage un reg tampering.

Tony

 

[gaswizzard]

.


Gaswizard can you confirm if the ones that you have been to ALL exhibit this behaviour i.e. D0 ignored on EACH fire regardless of D40 D41 for 50 seconds per fire.

.

The 4xx series installed CORRECTLY does NOT exhibit this behaviour , fitted lots of these boilers and NEVER had an issue , circulator sizing being paramount.

You have some of the best guys in the field giving up their time to help you on this , LISTEN to them. (831/mrv/bunny/bell) , ALL vaillant guys.

YOU HAVE A CIRCULATION ISSUE.

 

[UpgradeME]

I have not yet been convinced that there is really any problem with the OP's boiler operation.

So the above restated as (MM:SS):

WAIT --- BURN
00:00 --- 06:54
03:13 --- 00:03
02:52 --- 00:13
02:46 --- 00:15
02:44 --- 00:11
02:52 --- 00:07
02:44 --- 00:10

The above isn't normal/correct operation so there is an issue somewhere as the cylinder is still calling for heat... All the 4xx series can modulate down to 5-6kW so more info from the OP is needed (delta T figures will confirm if there is adequate circulation).

The part I have in mind is shown on that diagram but to be sure I would need to check the listing. Do you have a link to the whole document? Could be ein drossel klappe.

Ich spreche kein Deutsch, Englisch okay?

 

[gaswizzard]

I would not mention it here anyway as I dont encourage encourage un reg tampering.

I've posted it up for you in the CC , your input would be most welcome.

 

[Agile]

We do not know what the cyl stat is actually turning off at ( not what its indicated to be as they are notoriously inaccurate ).

Nor do we know what the actual cylinder temperature is.

Thats why I suggested the OP repeats the test with the flow turned up to about 75 C as that may give more headway above the cyl temp and the cyl stat setting.

It may well be the cyl stat is never being satisfied with the current settings of stat and boiler flow.

Tony

 

[scoobydo123]

Tony flow is currently set to 75 in the hope to put more heat into the cylinder for the initial burn. Cylinder stat is satisfied with current settings after many short burns often under 10 seconds and nothing even approaching 20 seconds, this is why I think I have a problem. Gaswizard thanks for confirmation that the ones you have seen do not do the 50 second malarky.

When I go round there I will do the following

Empty cylinder of hot water via bottom drain cock
Inspect cylinder with endoscope camera
Refill cylinder
Set up camera to record gas meter during reheat
Try to get as many D40 / D41 readings during first burn with timings
Monitor what D40 and D41 is when second burn starts
Try to get D40 D41 settings during 2nd burn this might be difficult if it behaves the same as when only 30L was drawn off.
If burns are very short then pull open CH valve for around 40 seconds and monitor D40 D41 if boiler does modulate.
Take photo of pipework around boiler and valves including ABV
Get a picture of PCB
Have a Grundfos 15/60 on order that I will fit on recommendation of you guys (although if this does not come before I can organise a visit then this will be after).

Anything else I should be doing

Thanks

 

[kevindgas]

sorry but i think there is an issue with the 400 series, not when running a 2 zone system via a VR65 but certainly when running a 3 zone system via a VR61 as has been seen by me since swapping from one to the other!

 

[kevindgas]

i have copied the reply to the above from the CC so that all can see.

MrV wrote:

kevindgas wrote:
sorry but i think there is an issue with the 400 series, not when running a 2 zone system via a VR65 but certainly when running a 3 zone system via a VR61 as has been seen by me since swapping from one to the other!

That was a bit of an unfair comment Kev. You haven't really explained the issue your having, or given any resolve a try, and the system installed isn't exactly designed to the correct specification that the vr61 is designed for.
You have also been receiving support to help bridge the compatibility issues.

maybe it is, but the design although good could be improved I believe with a software redesign thus eliminating the small problem I have experienced when the system is running for just UFH
the help you and others have given is very much appreciated don't think it isn't my suggestion is that simply Vaillant could surely with a little bit of effort make these systems work really well just by making the system run at different power levels according to the demands I:E a low fire when in UFH only a slightly higher fire for UFH/Heating or Heating/Hot water and a full fire when all three are required.
please don't think i'm critical, i'm only suggesting that the system could be improved to make it more compatable with various components surely that is the whole idea of research and developement.

 

[scoobydo123]

Currently round there and have emptied tank so far burn time is 22 minutes D0 currently at 11kw flow target 75 i have a flow of 63 and return of 54. I guess this is showing the cylinder is dispersing heat although only with a differential of 9 I have the timings of d40 and d41 on voice recorder so can publish when I get home. Still waiting for the first cycle to finish assuming cylinder does not become satisfied in the first burn. I believe that this is showing good circulation. Will give the rest of the results when they come in.

**UPDATE**

Right had to walk away after 1hr 10min of cylinder still not being satisfied and micro firing started after boiler switched off @ 1:04:14 brief account of events

Boiler fired d40 rose at about 1 deg per sec then started dropping off from 35 seconds after the gas valve actually opened (ie gas sign on display) so assume that this is when it took note of D0. Temp of D40 was 50 when this happened then the temp started dropping off from D40 down to 39 and D41 was down to 32. Other timings all elapsed
2min D40=45 D41=40
5min D40=52 D41=43
15min D40 =59 D41=50
27min D40=67 D41=58
34min D40=71 D41=63
39min D40=75 D41=67
@41minutes you could hear the boiler modulating as flow was 75 return 67 this continued until 1hr 4 min 24 seconds had elasped (boiler then shut down still with call for heat and code S7).
Boiler then went into micro fire mode with D40 dropping to 69 D41 67 and then 4 second burns with D40 shooting up very quickly and overshooting target flow rate.

below are some stills from the endoscope of the coil
View media item 44536

Untitled

• scoobydo123
• 3 Apr 2012
• 2

View media item 44534
Whilst I waited for the Cylinder to drain (which took ages) I decided to run some tests on the CH circuit. With it set @ 11Kw I could tell it was going to take an age to get any sort of heat out the system so set D0 to 22. This gave me a burn of over 40 minutes didn't time it properly but on restart after the boiler shut down with call for heat not satisfied I was then presented with micro firing on the CH circuit as well.

Does any of the above help.

Thanks