John, thank you very much for all that. It explains a lot that I hadn't appreciated. The boiler is an ecoTEC plus 618, with a separate sticker that says 'designation VU GB 186/5-5'. It looks like this
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$_86.JPG I hadn't appreciated that the boiler sensed whether it was heating the DHW or the rads. Presumably it recognises which thermostat is calling for heat, i.e. whether the cylinder t/stat or the house t/stat. As it's an S-plan system, I assumed that the boiler just came 'on', raised the hot water temperature to something close to the maximum set by the push-buttons on the front (target temperature and water pressure), and then got diverted to either the rads or the cylinder, or both, as required. I couldn't understand why the water got nice and hot when heating the DHW, but not when heating the rads, and I thought there might be a flow problem due to a blockage in the rads pipework somewhere.
I haven't explored the installer mode settings, in part because although I have both the operating instructions and the installation and maintenance instructions (recovered wet and soggy from the builder's skip where they had been dumped when the property was being modernised and the heating installed!), I couldn't see how to get into them, or even get a full menu up! I've since had a good fiddle, pushing buttons in pairs for example, and I can now access the full menu, but I've still not tried going into installer mode. As you say, there are lots of codes! I don't find the manuals a lot of help to the inexperienced like me. They're a bit like trying to learn how to play cricket simply from the rule book. OK for the details once you know what it's all about, but difficult to get started. Is there a general overview manual that got left in the skip, perhaps?
Off hand, do you know which code is appropriate for the maximum flow temp for heating? The manual leads me to think it's D.071, while D.020 is the max setting for the cylinder target temperature.
I am in the process of balancing the rads to get those last two to heat up. I'm surprised just how far closed the other lock-shield valves have to be turned to get those rads warm. Most of them are only open half a turn, and I may even close them a little further.
Thanks for the suggestion, but I can't see a similar feature listed in the various ebus codes in the Vaillant installation manual. The house t/stat does have a green eco setting, but it's not activated ATM.
Same boiler as my own, apart from mine being the cupboard mount version..
No, it can only do that, with the Vaillant ebus controls which then will provide split temperatures for CH versus HW provision.
A more basic control system means the Vaillant only has one boiler output temperature setting, which obviously has to be set for the higher HW heating need. Done that way, the boiler will often output more heat than is needed for CH, overheat the house, then cycle like that for some time, taking a long time to settle to a steady temperature. That simply because the boiler only knows that heat is needed.
With the Vaillant ebus controls, the CH settles the house and heating system quickly to what temperature you dial in, with no overshoot and because it knows the actual temperature and desired temperatures it can modulate much, much better.
I had just a basic control system on my new Vaillant, it would overshoot, then be too cold, then overshoot again. The pipes could be heard creaking as the heated and cooled, with each cycle of heating and cooling. There is none of that now, apart from when the CH first comes on and the house after which the temperature is held within a fraction of a degree.
In part because of not having the ability to split the boilers output temperatures and the cycling temperature variations, I decided I ought buy a full Vaillant ebus kit, to replace my old controls - with valuable advice from John Rumm.
Apart from the weird problem, which doesn't affect the rest of its operation, it has been a great buy and well worth adding the Vaillant controls. I guess it has saved some gas, but was worth it anyway for the extra comfort.
I have not checked how/if it can do split temp with non ebus controls, although the difference in flow temp you are seeing suggests its possible. I will investigate a bit further later.
S Plan is good here since with split temp, there is not really any occasion where running CH and DHW at the same time is useable.
One of the things the posher controls do is translate into English (if a tad Germanic at times) menu options.
Tis one of the things I have often found lacking in the Vaillant documentation - the big picture system overview stuff. Perhaps you only get that on their training course.
I do have a range of manuals I can lob your way however some may be useful.
You also have to get your head round the language that they use at times being a bit counter intuitive. For example having a zone controlled by a dedicated room stat, is typically an "uncontrolled" zone (a controlled one is where the boiler is in charge of a blending valve and so can reduce the flow temp into a zone independently of the flow temp on that zone).
I don't do codes at all on mine - however I may be able to reverse engineer some by comparing the boiler display of codes against the settings I have mode on my VR470 controller.
Possibly, but not guaranteed to work. It does work extremely well with the Vaillant boiler and Vaillant controls, using an outdoor sensor. You just dial in your desired times and temperatures, plus an adjustment factor which fine tunes your heating system to its environment.
I have the night set back temperature at 12.5C, which means it would never, ever need to fire during the night and the day temp set at
16.5C. That again means that it generally never needs to fire up.
The actual house temperature only rarely falls below 18C. During the course of the day I gradually adjust the desired temperature up a little at a time, to 20C in the hall - comfort temperature depends on how much physical activity I'm involved with. By evening time, I will usually have set the temperature to 20C.
Ramping it up gradually, means the Vaillant will avoid modulating up to maximum output for CH.
It cannot do split temperatures, with just basic controls - the boiler only receives a single demand for heat, or no demand, with no idea of what is demanding the heat. Hence there is only one boiler output temperature setting in the menu.
Once Vaillant ebus controls are added, the menu then includes separate boiler output temperature settings for CH versus HW.
Yup, having looked at my connection manual, I would agree - I recalled it had two separate inputs, but on closer inspection that appears to be a choice of mains or 24V controls, rather than fully independent ones.
Some of the older ones also had mechanical knobs on front to set them independently - which needless to say could be confusing in cases where the system was not configured to support it.
d.0 looks like it can be set to limit the maximum output in kW (should default to the boiler's max output)
d.5 can set the flow temp target (or return target), where D.17 sets whether its the flow or the return that is regulated (factory set to flow). Note that if there are ebus controls they can override this setting.
d.20 Probably only makes sense when the boiler can "see" the current cylinder temp. Note that contrary[1] to my expectation at the time, this is not achieved via ebus, but by a direct connection from a NTC Thermocouple in a pocket in the cylinder, that is connected directly to the boiler.
[1] I thought I had all the wiring in place for my system. I have a VR61 wiring concentrator / mixer unit that can (among very many other things) allow the system to control traditional S-Plan+ style valves, and I assumed things like the temp sensors would terminate here, but actually found I needed to install an extra cable to connect the cylinder temp sensor back to the boiler.
Thanks again for your replies, and thanks also to Harry. Further up this thread I got the impression that ebus or its equivalent was standard in all boilers, including Vaillants, but I now realise that it's an extra, that there is only one target temperature and that is simply set from the front panel without even calling up the main menu. In case I've not mentioned it, the DHW is unvented, like the CH, and there are two expansion vessels in the loft, but I don't see that as being at all relevant.
Which raises the question as to why my system seems to perform sluggishly when heating the rads, but as expected when heating the DHW tank. Harry said that before he fitted his ebus, the CH came up to temperature quickly and the pipes would creak as they expanded, only to cool again as the boiler went off. That sounds just like the way the older model Vaillant worked in my previous bungalow, and indeed how I expected this one here to work, which prompted my query.
Is there a flow-rate sensor in the water circulating through the boiler, such that if the flow-rate is low, the boiler heating is throttled back accordingly? If so, could a low flow rate be caused by having the lock-shield valves turned down too far? But I would have thought that that would just mean the water got up to temperature that much faster, and anyway, two of the rads, the ones I mentioned earlier as not getting very warm, have their l/s valves and TRV's wide open, so there should be adequate water in circulation.
Or could it be that the fancy Honeywell house T/S has something to do with it. I'm familiar with three-term PID temperature controllers for pottery kilns, which throttle back the heat input as the kiln approaches its set temperature so as to avoid overshoot. But I can't work out from the Honeywell blurb whether their thermostat does something similar.
Not all boilers have ebus, although I think all current Vaillants do. However you don't have to use ebus controls just because the boiler has the capability.
(personally I did since it enabled significant extra capabilities that I wanted)
Unvented DHW does not really change anything for the purposes of this discussion.
Why two expansion vessels OOI? (the boiler includes one for the CH side of things, you then normally only need an additional one for the cylinder)
Yup that is interesting. It would be interesting to see what the boiler is reporting for d.40 and d.41 during CH heating.
Also d.0, d.5, and d.71
(as an aside, when running, what icons show on the boilers LCD? - there is a icon of a tap for DHW heating mode, and a rad for CH mode - do you get both at once?)
Perhaps the boiler is seeing a return temp very close to the flow temp, and hence modulating right down...
Just a thought, have you checked the setting on the internal bypass valve? If that was set to a very low pressure, and you have a bit of flow restriction on the CH circuit, then the bulk of the flow might run though the bypass, convincing the boiler that the system is up to temp and not shedding much heat.
(I have my internal bypass pressure set very high, since I have some rads without TRVs, and so never need to cope with a completely obstructed flow path - so never expect the bypass will need to do anything. In a case where the house is warm, I would rather push extra flow through the non TRV rads since they share a space with the main stat, and hence should force it to cycle off once the house is warm enough)
That is the way most will work without weather compensation. I get the impression though that something is interfering with that on yours.
(On mine I find I can tell the outside temp when I wake in the morning just by listening to the pipe noise. On very cold mornings there will be more creaking and ticking as the pipes heat more / more quickly due to the higher flow temp)
There is d.37, but I suspect that might mean DHW flow rate and be applicable to the 800 series combis only.
See the comments above about the internal bypass. It could be interesting to run the boiler with the cover off, so you can feel the temp of the bypass pipe, and see if it feel like its taking lots of flow and getting hot - especially downstream of the valve. (or failing that just twiddle the screw to turn the bypass pressure right up)
(see section 5.8 in the install manual (email me if you need a copy))
If its only wired into the "call for heat" control on the boiler, it can't throttle as such, although it could be an optimising stat that attempts to compensate for the heating time constant of the house by shifting the demand times away from the actually programmed times, so that the target temps are met right at the time specified rather than the system start moving toward hitting them at that time.
(i.e. an optimising stat may learn that if you say you want it to be 20 degrees at 8am, it might need to fire the heating at 7:15 to actually make that happen. A non optimising stat will simply turn on a 8am and run until its 20 degrees at whatever time the in future that may be).
I did a little experiment: I opened up all the TRV's and L-S valves on the radiators, set the house t/stat to 30°C, and watched and waited. On the older Vaillant in my previous property, that would have brought the burner in on nearly full blast until the water temperature approached the set target (about 65°C), when it would modulate back, and it would only take a fairly short time, say a few minutes, to get there.
But here, the water temperature rose only very slowly, taking about an hour to reach the maximum target of 70°C from a starting temperature of about 35°C, and the burner bar (the little inverted triangle on the LHS of the LED display), rose only slowly to about half way, but never any higher, as the water temperature came up. It was as if they were moving together, but slowly.
While the water temperature was slowly coming up, I took a few readings on the parameters you suggested, as follows:
D.000 Heating partial load - Auto D.005 Flow Temperature Target Value - 70°C D.037 There is no D037; it jumps from D036 to D039 (as it does in the list in the manual) D.040 Flow Temperature Actual - 43°C D.041 Return Temperature Actual - 39°C D.071 Maximum Heating Target Flow Temperature - 75°C
I note that the flow and return temperatures are only 4°C apart, which may be relevant to your point that if there's not much difference between them, the boiler may be modulating right down as a result.
Some of the other things you asked about:
I have no idea why the plumber put two expansion vessels in the loft. As you say, there's one in the boiler anyway.
I checked the setting on the internal bypass valve; it was set about mid-way, i.e. roughly five full turns from either end, as the manual suggests, but I didn't feel the bypass pipes to see if they were hot because I wasn't immediately sure which pipes they were. By doing a bit of feeling around subsequently, I think I've located them. Which is the downstream pipe - the one that comes forward from the valve, at the front, or the one that goes across, at the back?
I did notice in the manual (section 8.4 Setting the bypass valve) that it said if the bypass valve pressure is increased, and the pump output is set to less that 100%, things may not work properly, and then the pump output (D.014) should be set to 5 = 100%.
Currently, D.014 Pump Speed Target Value - 0 Auto.
I never see the little tap symbol in the display; there is a radiator symbol permanently displayed on the RHS, and when the house t/stat calls for heat, a flashing radiator symbol appears on the LHS above the position where the tap symbol would normally be.
Well, with all valves wide open, the system is going to be unbalanced, so a lot of the flow will take the easiest circuit and not drop much in the process ...
Change the D.000 "heating partial Load" from Auto to whatever the boiler CH heat output is ie 24kW , I dont believe this is critical. This solved exactlt the same problem on my new Valliant.
Also if your boiler has an Installer Setting - Appliance config - Green IQ - try turning this off . Only relevant if your boiler is a Green IQ model.
Hmm...I take your point, but all the rads started to get warm, and I would expect with the largest rad area available to the hot water, the heat loss and hence temperature drop would be greatest, which is why I did it. But I'll try throttling back the rads via their l-s valves next time and see what happens.
Interesting comment. I take it your model is the next one up from mine. Mine is only 19kW, I believe. I'll try that the next time I fiddle with it! Thanks.
I'm not aware that mine is a Green model, but I'll explore the Appliance config settings.
Just had a look and no mention of Green IQ in there AFAICT.
If you fully open all the TRVs and lock shields you may create a system which is highly unbalanced, with the lions share of the flow going through one or two rads. This might skew the results a bit.
What does the burner output bar show when heating the cylinder?
I might be tempted to set that at a value - say 10 or 15kW and see if you get different behaviour...
(IIRC there is also a test program you can run in the installer menu that runs the burner at full power)
Sorry my bad, d.36 is described as Hot water flow sensor with an output in l/min
Sometimes they add an extra one on a system with lots of rads. (having said that I have 21 rads on just the internal vessel). So perhaps you have one as an extra CH one, and another for the unvented cylinder.
I am guessing that the one coming from the front is the main CH return.
ok in a sense that is reassuring - I would only expect that if the boiler knows that its doing a DHW reheat.
I think the rad symbol on mine only flashes when there is a demand, but the boiler is not firing (say due to being in an anti cycling timeout)...
I am at long last beginning, just beginning, to understand it. The situation confused me because the house thermostat has a proportional setting that comes into play either 1.5 or 3.5°C before the set point, to slow up the rise in house temperature and stop it overshooting. This, combined with a rather slow start-up on the Vaillant, meant that the Vaillant would get cut out by the t'stat before it had properly settled down into it's firing routine.
There seems to be about 30 seconds delay when the t'stat calls for heat, during which time the burner comes on at a low setting, and what I presume are the pump and fan come up to speed, before the burner comes up to full blast as defined by D.000 (thanks to both JR and Robert for suggesting I change this setting; it has improved things a lot). But partly because of that delay, the burner barely has time to warm any water before the house t/stat cuts it out as part of it's proportional control. Grrr! I see no way of over-riding this proportional band in the house t/stat, nor of shortening the period of time the burner runs at a low setting before coming up to full blast.
I'm going to temporarily replace the house t/stat with a nice simple mechanical one, that just switches off/on with no exotic complications, while I get the boiler doing what I want and the rads properly balanced. Then I'll swap back to the previous t/stat and see how it goes.
For JR: the burner bar comes up to between 1/4 and 1/3 when it's heating the DHW tank, and the output temperature on the boiler gets to around 70°C with no difficulty. That side of things is OK, but of course there isn't a proportional control in the DHW tank t/stat!
For Harry B: I noticed as I was browsing through the various diagnostic codes for the boiler, that code D. 018, Pump operating mode setting, could take one of two values: quote "1 = Comfort (continuously operating pump). Internal pump is switched on when the heating flow temperature is not at Heating Off and the heat requirement is enabled via the external controller. 3 = Eco (intermittently operating pump). Internal pump is switched on every 25 minutes for 5 minutes once the overrun time has elapsed" (there is no setting 2).
It explains to me why I often hear the boiler 'working' even though it's not fired up for a while. It may not be the same as your query, because I think you said yours actually fired up briefly and you have an eBUS controller, but it may be worth looking at the various diagnostic codes to see if there's anything there that looks familiar.
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