There are [hopefully going to be] several people who have contributed detailed information about the cycling problem with their 400-series boiler, which can be found in the documents stored here. [N.B. when you click on the word "here" at the end of the previous sentence, you should be taken to a Google docs page containing several documents, one for each user and an uncompleted form called "_Template". One user has reported that he does not see this. At the moment it's not clear why not, but if you'd like a copy of the document emailed directly to you, please contact us at the email address on the "Contact" page.]
If you'd like to contribute your own experiences, we'd be very pleased to add them too. Please do so by following the same link and filling out the form in the "_Template" document, not by adding a comment to this page. If you have suggestions as to how the form might be improved, feel free to add a comment or email us.
Whilst I think this is a great idea to have a single place for all the info, I don't think it is as straight forward an issue as shown on here.
ReplyDeleteIt's not clear to me (being a non boiler engineer) how it is _supposed_ to operate?
i.e. In a house with TRV's, as the house comes up to temp and the TRV's switch off, unless there is >5kW of heat being 'dispersed' on the system, even at the lowest output, there is too much heat (kW) generated so the boiler will cycle off.
Perhaps you could define what time period would be considered "short cycling" and what would be normal operation at differing outside temps?
Rad sizes (over or undersized for the room) will also affect the boiler cycling along with the various d.x settings and whole house heat loss / boiler size / d.xx settings.
Perhaps you should add in the common d.xx settings e.g. d.0, d.1, d.2, d.17 (+others if not set to DHW priority) the IDHEE kW size (http://www.idhee.org.uk/calculator.html) and for completeness kW output from rads to your template!?
The issue is not exclusive to the VRC430 / Weather Compensation. The VRT392 which also has modulated flow control for water temperature also has the same issue. In simple terms, the 392 works in a similar way to the 430 but only uses inside temperature rather than outside temp & inside temp to regulate the flow temperature.
The 392 is also missing a "minimum flow temp" setting which makes masking the short/micro cycling all the more difficult. The only way I found was to set d.17 to return regulation which has the effect of increasing the minimum flow temperature and stopping the micro cycling.
This may also be of some use, which explains how the 'anti-cycle' operates.
ReplyDeleteVaillant d.2 code - Example of operation
Lets assume d.2 is set at 60, the modulating controller is currently requesting a flow temperature of 40C and the burner has already fired. The boiler upon entering anti-cycle mode starts a timer with an initial 'goal' of waiting 38.5minutes (from the Table below).
If after waiting 20 mins, the room temperature drops, the controller then changes it's flow temperature request from 40C to say 60C. The anti-cycle time for 60C is 17 mins, as the timer has already reached 20 mins, there is no anti-cycle time remaining (it's actually now -3mins) so the boiler then fires the burner again.
[timer] - [current waiting time from Table] = [d.2 time]
Initially that would have been be 0-38.5=38.5mins then changed to 17-20=-3mins
The above example is assuming a modulating controller set in 'analog' mode where the flow temperature demand is dynamic. If set to 'two-point' mode (or using a.n.other room stat), the flow temperature is static and set via the dial on the front of the boiler. As an example for a static flow temperature demand, if the boiler was set at 65C, after it enters anti-cycle mode the boiler will wait 11.5 minutes before firing again with d.2 set at 60, or 4.5mins with d.2 set at it's default of 20.Pump is off and zone valve(s) are closed during anti-cycling period."
[TABLE - Not sure how this will display?]
TFlow Set maximum burner blocking time [min]
°C 1 5 10 15 20 25 30 35 40 45 50 55 60
20 2 5 10 15 20 25 30 35 40 45 50 55 60
25 2 4.5 9.2 14 18.5 23 27.5 32 36.5 41 45 50 54.5
30 2 4 8.5 12.5 16.5 20.5 25 29 33 37 41 45 49.5
35 2 4 7.5 11 15 18.5 22 25.5 29.5 33 36.5 40.5 44
40 2 3.5 6.5 10 13 16.5 19.5 22.5 26 29 32 35.5 38.5
45 2 3 6 8.5 11.5 14 17 19.5 22.5 25 27.5 30.5 33
50 2 3 5 7.5 9.5 12 14 16.5 18.5 21 23.5 25.5 28
55 2 2.5 4.5 6 8 10 11.5 13.5 15 17 19 20.5 22.5
60 2 2 3.5 5 6 7.5 9 10.5 11.5 13 14.5 15.5 17
65 2 1.5 2.5 3.5 4.5 5.5 6.5 7 8 9 10 11 11.5
70 2 1.5 2 2.5 2.5 3 3.5 4 4.5 5 5.5 6 6.5
75 2 1 1 1 1 1 1 1 1 1 1 1 1
UpgradeME,
ReplyDeleteThanks very much for your comments. Your point about defining what is 'normal' is a good one. It might be that short firing is the normal behaviour - certainly it is the behaviour that I have observed when logging data from a 600-series boiler with a VRC430f, for comparison with my 400-series. However, it does not seem a very sensible normal behaviour in circumstances where the heat demand from a house exceeds the minimum temperature to which the boiler will modulate. It would be interesting to hear from Vaillant whether they consider short firing to be normal, and if so, what it's supposed to achieve.
You are quite right that, when the house is warm enough or when the weather is warm enough, there will be occasions when the heat demand is less than the minimum that the boiler can deliver. If the boiler fired continuously in such circumstances, the house would heat up too much.
What we mean by 'short' firing is that the cycling on and off is seen when such conditions do not prevail. In other words, the boiler cycles on and off even though the heat demand is enough to warrant continuous firing. In my case, I know that on this definition there is short firing with my boiler because, when I turn off Pump Delay Time to achieve continuous firing, the house comfortably maintains the correct temperature and does not overheat.
Otherwise, it's hard to put arbitrary time limits on what constitutes short firing. In practice in my case the short firing seems to be always for less than 30min, and rarely if ever more than 20min. Alternatively, it seems pretty unlikely - unless you have an incredibly well-insulated house - that when the outside temperature is 5C or less and all radiators are requiring heat (e.g. first thing in the morning), any observed non-continuous firing is due to the required output dipping below 5kW. In any case, you're right that we should clarify exactly what we mean by it.
Your suggestions for adding to the template are good ones, and I shall have a look at that.
Where does your information on d.2 come from?
I found the d.2 table during my own investigations last year (someone pointed it out to me from another manual) and the text is a combination of text from Vaillant manuals, other posters on Diynot forums and my own observations.
ReplyDeleteHaving vrDialog would have been a great help when I was carrying out my tests but I couldn't justify the £70+ cost (especially as I know it would cost less than $2 to produce commercially!) so I had to resort to manually watching the boiler operation when making changes and never did create a (nice) graph like shown on here for on/off cycling times.. :(
As a visual person, it would be great to see what 'should' happen to compare against (or debate) what you have graphed for your boiler with regards to micro/short cycling!?
I would 'assume' that on a cold winters morning, initially the boiler would be on continuously until the room temp approaches set temp. After the room/house has reached set temp, the boiler will cycle on/off for varying lengths of time depending on insulation, outside temp, movement (doors opening etc) inside etc. If the initial 'continuous' period above is 'cycling', then I would envisage the system is not working 'as designed' by Vaillant (assuming the rest of the plumbing/rads etc is upto specification).
From my reading of Diynot, it would appear there are often boilers installed which are over-sized for the property, boilers that haven't been commissioned (i.e. d.0 set correctly for the property) and any number of other factors which affect how the systems operate.
The reason I mention this is professionally, I have worked in an enviroment where technical issues such as this were investigated (not in this industry). In my experience, the 'best' way to get Vaillant interested will probably be to make life as easy as possible for them to resolve it. Providing them with structured information / data of what you expect to happen and what does happen along with as many variables as possible (i.e. d.x settings, IDHEE kW, TRV's, Rads, typical outside temp when issues occur etc) to elimanate their engineers just dismissing it and taking you seriously.
If the new VRC470/VRT370 fixes the "cycling issue", be prepared for Vaillant's response to be along the lines of "working as designed" for the VRC430/VRT392!
Finally, just for completeness, I also found that the Glow worm Ultracom HXi are a cut-down version of the Vaillant ecoTEC 400 series (Glow worm is a Vaillant Group brand, the ecoTEC 400 series were launched in Sept 2006 and the Ultracom in Mar 2007). There are also Glow worm branded equivilents of the various controls which combined are likely to exhibit the same issue!
I see that a legible image of the d.2 table is included in your thread at http://www.diynot.com/forums/viewtopic.php?p=1936820
ReplyDeleteDo you understand that this timing mechanism using d.2 comes into play only when the boiler has entered state S.8 (anti cycling mode)?
With regard to what should happen, I agree with you. For a visual representation, see the graphs in the new section headed "How should it look?" that I have just added to the page "The problem".
The d.2 Table came from this manual http://www.vaillant.co.uk/stepone2/data/downloads/4b/43/00/ecotec-exclusive-installation-manual.pdf
ReplyDelete... and yes, I understand how / when the anti-cycling (and pump over-run) come into play during cycling! I guess the above may not make it clear (I just cut that text from a spreadsheet I created for my ref and maybe doesn't explain it all!? :) )
The new graphs look good, as I assumed it 'should' work.. I would love to know (see) how mine is working now, I might have a play with a IR camera I have to see if I can record the LCD display for 'movement' which will create me a log I can drop into Excel! :) - It won't give me all the temps but should record any cycling on/off times? #CreativeSolutions
As you have vrDialog, is it possible to plot burner output (kW), temperature demand, actual flow & return temp on the same graph? Here's why I think micro firing occurs on many installations:-
ReplyDeleteWhen the house does not need much heat (perhaps when most of the TRV's are off & the requested flow temp is say 40C), logically the burner should start at it's minimum and work upwards if necessary. I don't believe this is the case with the 400 series. I believe they have a 'bug', the burner initially fires at a higher rate and then modulates itself down after xx seconds.
The problem occurs when the initial higher burner rate causes the flow temp to increase to the requested temp in seconds so the boiler cuts out (your 'Micro firing') before it has chance to modulate down to its minimum power output approx 5kW.
I have a hunch it may be due to some kind of emmision regulation but may not be for this country or even specifically for this boiler! (You will see from the diynot post you linked above, the same software / firmware has been used across a range of boilers. e.g. the 400 series does not contain a pump (that's in the system / combi models) but the settings in the software are still there! ;-)
If you could plot what is happening with the burner output (if that's not plottable, perhaps gas usage?) and flow/return temp's you may be able to highlight the actual cause/affect using Vaillants own diagnostic tools! ;-)
My question "Do you understand that..." was intended to have the sense "Is it your understanding that..." (since I don't have a clue!) rather than "You fool, don't you even understand that..."!
ReplyDeleteYour ideas about the source of micro firing are interesting. Sadly vrDialog does not record burner output or gas usage. The best surrogate that I've found is fan speed, but I doubt that that the correlation is at all linear. There is an additional problem that the micro firing happens on a timescale much shorter than vrDialog can record, since (although it can record parameters frequently, at 10s or even 1s intervals) it takes about 50s to refresh all of its parameters.
The problem I have is that the minimum modulated output of the boiler 5kw eventuly exceeds the heat required, even though the room is still not upto temperature. The reason for this is the radiators cannot disparate enough heat and I only get about a 10C drop from the inlet d41 to the flow output d40. So when d40 reaches target flow temperature the boiler switches off and waits (I have no idea what criteria other than d67) and then re-fires. Up until this point I understand what is happening and except this will happen as the radiators are a bit small and the house is very well insulated. My problem is that when it restarts it overshoots the flow temperature and can get into a cycle. The ways to get around this have been to set the minimum flow temperature of 55C, derate the boiler which prolongs the time to reach the problem set d67 to 60, run my pump on high, also have all radiators on.
ReplyDeleteAlthough this works not to bad in the cold weather and is probably not making much difference to efficiency my problem will start when the weather warms up and ideally i will be looking at flow temperatures well below 55C.
I cannot understand why there is not a way to reduce the output for that first 60 second burst, if that was lower I'm sure most of my problems would go away.
Looking forward to seeing what comes of this Blog.
Gary in Coventry.
Completely agree with UpgradeMe about the boiler settings - I see you have done the template but could you post up your own settings?
ReplyDeletePraise be to UpgradeMe for his d2 table which is not in my 415 manual. I spent many happy days working out my own version. The a***s at Vaillant had no information to offer despite explicit requests.
Would this be correct? Short cycling means any cycling which is unhelpful to the heating goals
and which is voluntarily engaged in by the control mechanism rather than because flow temp exceeds maximum? Then short cycling is a bad thing and you seem to have serendipitously abolished it by setting C21. Hallelujah!
Normal cycling happens when the boiler exceeds target flow temperature setting and switches off to avoid overheating but restarts again effectively in a timely way.
What I think you refer to as Microfiring is a form of Abnormal cycling. The boiler stops because target flow temperature is exceeded but tries again before this is possible, rapidly overheats and stops again. The temperature fall needed before a successful restart depends on all kinds of things but key is the flow through the boiler. For the 415 at the minimum flow rate of 10.6 litres/sec with 12kw fixed input during first minute the return needs to fall 15C below target. That can take a good while and d2 needs to be set appropriately.
I have d2=55. Even with the maximum d2=60 that will only take me down to 45C minimum flow temp in my extremely challengingly tiny and well-insulated environment.
I suspect that if you tune d2 a lot longer, you may be able to get rid of microfiring and still have good low targets in your large house.
Mike,
ReplyDeleteI have added my boiler settings, which are:
d0 = 27 (presumably kW)
d1 = 5 (presumably minutes)
d2 = 20 (presumably minutes)
I agree entirely with your description of short cycling, normal cycling and micro firing.
The importance of UpgradeME's description of d2 operation is only just beginning to sink in. My d2 setting (which I suspect is just the default one) may well be much too short. In the interests of maintaining a structured approach to providing and discussing information, I intend to put the d2 table and explanation into a blog post on the home page, with my queries as to what it all means, and then we can have a d2-specific discussion there.
Gary,
ReplyDeleteI believe the "first 60 seconds" is not always SIXTY seconds on all 400 series boilers. I haven't worked out if it's a firmware version change, a attached component or system board revision.
e.g. On mine, it only last for approx 20 seconds and is affected by d.0 however, I understand that on some models, d.0 has no affect to burner output and it last approx 60 seconds
I read from a senior Vaillant engineer on diynot that the burner runs at 80% of the boiler's full power for 60 seconds (which is not correct on mine).
On my 418, I believe the burner runs at 80% of d.0 kW for the first 20 seconds. I have not been able to absolutly confirm this though so is an approx based on observations and many tests last year.
When did UpgradeMe get his boiler? My 415 is 3yrs. It definitely gives 12kw out of 15kw for about 55 seconds and this is irrespective of d0.
ReplyDeleteI'm thinking if I should be pursuing those b*******s at Vaillant for this change which they said nothing about when they were stone-walling my complaints. Problem is I mostly have it tamed now after a fashion. What if they changed something else and then I can't fix it? They are not exactly forthcoming with information so I would not be able assess the risk.
20 seconds versus 55 would make the "delay tank" I have plumbed into my bypass circuit redundant but otherwise d40 has usually maxed by 20 seconds. 80% of my d0 of 10kw would make a huge difference though - system should restart after cooling 10C rather than 15C that would be excellent.
Which of the problems do you have and why?
MikeH,
ReplyDeleteMy boiler was installed about a year ago, I fitted (upgraded) the controls (VRT392/VR65/VR10) myself afterwards.
The problem I have is 'micro firing' when I have d.17 set to default (flow) & moderate outside temps (I use d.17 as a work-a-round as the VRT392 doesn't have a minimum flow temp setting!) d.17 set to return regulation increases the flow temp so negates some of the 'benefits' of fully modulating but "fixes" micro firing for me.
NOTE: During the initial 20 seconds (with d.17 set to flow), if the requested flow temp is low (say 43C) the return temp quickly rises to approx same temp and the boiler starts its micro-firing cycling.
After 'fixing' micro-firing with d.17, I'm not sure if I have 'short cycling' or 'normal operation' for my system without logging it. I see cycling but not convinced if it's a problem without the logs.
Hello,
ReplyDeleteI'm just now at the beginning of what looks like it may be a long and painful learning curve.
I have just had a EcoTech Plus 428 fitted with VRC470f and VR65. As my HWS tank isn't a uniSTOR I don't have the VR10 fitted.
Having read many posts on diynot I am going to make the VR10 an option in a dry pocket just above the coil, which is where it would be in a uniSTOR, so I MAY get better control over the hot water, but I plan to keep the regular cylinder-stat wired in, just set somewhat higher.
Back to the existign installation - my installer seems as baffled by the boiler's cycling antics as I am, and Vaillant don't seem to be helping him either - so far.
I don't have access to a vrDialog, but I can confirm my new boiler is cycling, micro-cycling, and failing woefully at any attempt to achieve its targets. Set 24°C, let it run all day, it might hit 21.5°C. Not good.
Initially I suspected the issues to be related to possible airlocks in the long (and inaccessible) 28mm L-shaped flow/return pipework between boiler (in garage) and control gear in airing cupboard.
My system has history of being a pain to re-fill, and there is still a little air percolating around now, but after 3-4 days I've seen that sometimes the boiler will fire up for many minutes with sensible differentials, suggesting flow isn't an issue, but at other (most) times it cycles like crazy.
I was thinking of investing in an automatic bypass, instead of a existing gate valve, to maximise flow to where it's needed i.e. into the 13 radiators with TRVs and the 2 with lockshields that are balanced to allow system control via roomstat, or rather now via VRC470f. That may be a good move, but seems unlikely to resolve the cycling.
Now though, after encountering this blog, I'm thinking of investing in vrDialog, but I'm also wondering when a revised PCB might be available to me too...
Thanks for creating this blog, at least we are not alone!
Hi bbstrikesagain,
DeleteYour described behaviour is certainly consistent with the issue that has beset several others. Of course there may be a different or additional problem, but if you say to me EcoTec 428 and VRC470f, it certainly raises in my mind the notion that your cycling issues are nothing to do with airlocks and everything to do with the boiler PCB. Come to think of it, I don't think I know of a single person who has reported that they do not experience cycling with that sort of combination - although there are doubtless many who proceed in blissful ignorance of the perpetual cycling that is taking place.
I've certainly learned a great deal from having vrDialog, and have used it to observe the microfiring in all its glory, but whether or not it would usefully tell you more than you know already is perhaps questionable. I wish I could tell you when the revised PCB might be available, but I still have no information about that.
Good luck with resolving it all.
Finally I have vrDialog working. I had to run it in a virtual Windows XP Home machine inside VMware player as I couldn't get it to work under Windows 7 64bit, but it works fine like that. Apparently later versions of Windows and devices like my VRC470f will need a forthcoming vrDialog replacement, to be called something like commsDialog.
ReplyDeleteI calculated that my Grundfos 15-50 and Honeywell DU144A need replacing to meet the 428's minimum flow specs - a 15-60 and a Myson ABV22S should do it justice - so I will investigate and post more results when the hydraulics are up to spec. In the meantime I can report that I have identified some cycling and micro-cycling that cannot relate to the slightly low flow...
After the system's been on for a long while it goes into cycling, on for 1m30s, then off for 3m30s, the turn off trigger apparently being a sudden increase in return temperature - I see this as hot water having made a full circuit, perhaps through the bypass.
The micro-cycles occur when the system has gone into set-back which seems really odd, with
I posted a fisrt snapshot at:
https://dl.dropbox.com/u/20135218/Vaillant/First_log_428_%2815-50%29.png
The heating has coped with the recent warm/cold/warm spells, but I'm not sure it should really be cycling and micro-cycling...
More to follow.
Hi,
ReplyDeleteAny progress on the new prototype PCB that Vaillant supplied? Has it eliminated the cycling issues?
Unfortunately I have no further information about it. Vaillant has not responded to my queries as to when it will be available.
DeleteI also have not used the boiler since October (for unrelated, house refurbishment, reasons). However, it worked fine with the new PCB up until that point.
Hi, below is a copy of an email sent to Vaillant technical this evening and clearly relates to the above blog,I don't undestand alot of the d factors mentioned,looks like I have been captured 2 boilers not performing as they should.
ReplyDeleteGood evening
3 years ago I changed my boiler to a Vaillant ecotech 318 as recommended by the gas installer, having changed the boiler every winter the boiler struggled to reach 21° temp in our lounge, I was convinced that the boiler was too small, but my installer stated that it was the same size as the one removed.
I put a new 3 way valve, an energy efficient pressure pump and a programable room thermostat to try and make the system more efficient,but to no avail.
My house size is 4 bed detached ensuite etc with 11 rads, 3 of which are doubles.
Having gone on your site and plugged in the house spec, it came up with a 438 or a 428 (eco tech plus) as an alternative.
So I decided to bite the bullet and had a 428 installed and find that although its a little better it still doesn't appear to pump out the heat, the boiler tends to fire up and knock itself on and of with regularity much the same as the previous boiler.
I read a review tonight from the which magazine which mentioned the same boiler overshooting and knocking itself off and resetting much the same as what mine is doing, and having cleared debris from the system, it now heats up and stays that way without overshooting until the house heats up, alarm bells started ringing as to whether my boiler is performing as it should.
Currently it is 0° outside and my heating has been on since 1.30am and the thermostat is showing 20° set for 21.5°I,m wondering if my boiler is doing what it should do, should it be knocking itself on and off by racing to @ 76/77° then dropping down to @ 46° and repeating the above cycle, the bolier was swapped about a month ago and there is still air in the system.
Is the boiler performing correctly
Martin, you're particularly unfortunate to have suffered this with two boilers. My impression has always been that the 318 does not suffer from the microfiring problem described here, so it may be that there is something else wrong with your set-up. However, your current rapid on-off cycling with the 428 does sound like the microfiring software problem.
ReplyDeleteYes and having now paid more attention, it actually goes down to around 46° then fires steadily to @ 75°, (takes around 2 mins) knocks off then drops to around 68° then the full burners appear to kick in and it fires to to anything upwards of 76 to 79° then drops down to @46 and starts all over again.
ReplyDeleteHaving had the boiler such a short time, it is still under guarante, could it be considered defective?
Is there a fix for this issue or is it one Vaillant are ignoring, I still haven't received a reply from Vaillant technical as yet.
Cheers
If this is indeed the same problem as the one I have experienced, then the only fix I know about is the one involving the new circuit board that I describe on this blog. It is not, so for as I know, publicly available yet, and I have no information as to when it will be - Vaillant's communication is notoriously poor.
DeleteOf course, my experience of this problem is during weather compensation, with much lower flow temperatures than the high-70s that you are seeing. It's a bit surprising that a cold house cannot lower the return temperature enough for the boiler to fire continuously in your case, which is why there may be something else going on for you. More than that, I cannot say.
There is clearly something wrong with your system. If it's the boiler that's the cause (rather than the combination of pump and pipework, for instance), then I'd say the boiler is defective.
I called vaillant with them not having responded to my email, eventually I spoke to an operative who advised that when the raditor is flashing and it I thinj she said S53 when the i is pressed then the return is not hot enough which puts the boiler into cycle so its she said its my system thats at fault, but having checked, when it goes to te cycle it goes through the S numbers finishing with pump over run and then sometimes goes to @68 and re fires and sometimes to @48 and goes through the cycle again. I have contacted by installer who asked me to fully open the pump bypass and let it run which it did, only knocking off once during the hour it was running, I have an air seperator on the system and he thinks there may be an issue with this being gunged up so is going to remove it and just put a couple of T joints which may sort the issue if indeed it is sytem generated, otherwise back to Vaillant, the system has already been machine cleaned, my first boiler was a potterton profile and the system worked fine, so I cannot imagine why there should be an issue with aa new boiler manufacturer.
ReplyDeleteWe have had problems with s53 ever since our 428 was installed over five years ago. It has cost us more in service charges, flushings, etc. in that time than our old Potterton did in more than 25 years. No one seems able to make a permanent fix to the problem.
ReplyDeleteWe have an ecoTEC plus 418 and are experiencing short/micro firing - every 5 minutes or so with the ignition firing for about 2 minutes before switching off again. The trigger temperature appears to be about 46 degrees C, temp climbs rapidly to 69 deg.C, the ignition pauses until the temp drops down to about 66C and it then fires again briefly to 73C before shutting off.
ReplyDeleteOnce the temp then drops to 46 or thereabouts, a few minutes later, the ignition fires again and it starts all over.
We don't have weather compensation installed.