What is the power limit in the Junkers Cerapur Smart 5C 24kW boiler?

Question

Hello I wonder what the power limit in the boiler is. It is often read that someone reduced from 24kW to 12kW, What does it do? I look at my Junkers Cerapur Smart 5C 24kW boiler with underfloor heating in the CW400 controller and it shows that the minimum power is 12% and usually it works at...

badboy84 · Answer

This is probably about the connection options that power the boiler.

bumble · Answer

What this means is that the boiler starts at the moment of ignition with maximum power, then modulates to low power and increases the power to meet the demand. Now it may be different in new boilers. There is no need for the boiler to run at full capacity every time it is started.
The maximum boiler power will be 12kW. If the boiler is oversized and too large, it will not work with as much power anyway. However, reducing the boiler power will have a negative impact on domestic hot water heating. If we lower the maximum power for domestic hot water.

Wojewoda82 · Answer

Limitation of max power for CO (because it makes some sense here):
a) the boiler is quieter (at max power, a condensing boiler is louder than, for example, at half the available power), it matters if you have the boiler, e.g. in the kitchen
b) slower heating of the central heating system - so that the heating cycles are longer, and thus the comfort and durability of the boiler (smaller cycle times), e.g. in the case of radiators (especially if they are a bit small)
c) boiler efficiency is best at minimum power, the closer to maximum power, the lower the efficiency - for some time after firing, a throttled boiler operates with better efficiency than if it were running at 100%.

I also have it throttled to 10KW (from 20KW to central heating)

BUCKS · Answer

This is an individual matter. If someone has, for example, a domestic hot water tank whose coil has a lower power than the maximum power of the boiler, this power should be adjusted to the power of the coil. If necessary, we lower the maximum power. In this case, limiting the maximum power may affect the boiler`s operating characteristics. If someone has an ON/OFF room regulator, the regulator does not communicate with the boiler and does not control its power, but only gives a heating signal or turns it off, and the heating process is carried out according to the algorithm that is installed in the built-in electronics that controls the operation of the boiler. Currently, boilers have a set start power, i.e. the boiler can start with a defined power but then goes to maximum power and starts modulating if necessary. Too high a maximum power may result in the burner not heating smoothly, but sometimes it will heat more strongly, and in a moment it will reduce the power and there will be a sine wave in the boiler`s heating power. In my opinion, there is no point in setting the maximum for more than the power needed for frost -20, but ultimately, everyone sets the boiler according to their own needs. The practice is that most people leave it as set by the installer and do not change anything because they are afraid and do not know what to set and how to set it. And in my opinion, each case should be considered individually, because the maximum power is one thing, but the minimum power of the boiler is important. Anyway, everyone has a different sense of what is good and what is bad. For example, I was at home where the radiators were clearly humming, which indicated that the pump capacity was too high, but the owner claimed that it was OK and saw no need to change anything. I would immediately change the settings and look for the optimal settings, while someone else doesn`t care and doesn`t care. Added after 24 [minutes]: I would argue a bit here. Apparently, boilers have the highest efficiency at 100% power, but in the case of condensate, there is additional efficiency resulting from condensation, which gives the marketing efficiency above 100%. And a boiler operating at 100% capacity would eventually reach the boiler water temperature where condensation no longer occurs, so the overall efficiency of the condensing boiler ultimately decreases because we lose several percent of efficiency due to the lack of condensation. In other words, even if the boiler operates at partial power with lower efficiency, it gains an additional percentage of efficiency from the condensation effect, so in the end we gain more than we lose due to the lower power, which means the global balance is positive.

bumble · Answer

I have a Junkers condensate boiler ZSB14-3C and its power is limited to 75% and even then it is too high because at frosts of -25 the boiler operates at a maximum temperature of 52-54 degrees. However, for hot water I have a 125l jacketed tank and it heats water up to 45 degrees in about 35 minutes. but with the limit to 75% it takes probably 1.5 hours. In the case of hot water, the circulation temperature at unlimited power is about 85 degrees, and at limited power it is only 60 degrees.

rustin · Answer

If my boiler runs on max. CO20% most of the time, what will be the effect of limiting the power to e.g. 12kW? If the boiler modulates from, say, 3kW, because that`s what it says in its specification, after limiting it, it won`t be from 1kW?

bumble · Answer

So if it`s 20%, why so big? You had it explained.

rustin · Answer

Is that what I`m asking? And if it were smaller, it would work with a power of 2kW instead of 3kW. Let`s stick to the question, one bought out of ignorance Added after 2 [minutes]: This is definitely not the case in the boiler I have and it is mentioned in the first post

bumble · Answer

And with what power does your boiler turn on the burner?

rustin · Answer

Today I will check carefully and tell you. I may be wrong, but I think I saw it once.

bumble · Answer

Choosing of course is all about Limiting the power helps keep the boiler from condensing too. If you have the option of heating the room quickly and not comfort or eco, use high or even maximum power.

BUCKS · Answer

Most boilers are as already written, i.e. they start at starting power and after a few or a dozen or so seconds they switch to maximum power. But such a scenario occurs if you have an ON/OFF regulator and you have an original that communicates with the boiler and controls its power, so the boiler will automatically have different operating characteristics. I suspect that if you disconnected your regulator and connected, for example, Salus, Euroster, Auraton, i.e. a regular ON/OFF regulator, it would be as I wrote, or as my colleagues wrote above. Basically, you already got the answers but you don`t understand them and that`s the problem. To understand it, you need to have the basics, without the basics it is difficult to understand. To sum up, if you don`t need to reduce the maximum power, don`t change it and that`s it. The power is reduced to adapt to the installation, because, for example, the boiler has large power fluctuations and the burner operates not with constant power but with a continuous sinusoidal wave, because the boiler produces too much heat than the installation can absorb. Or, as I have already written, the power of the hot water tank coil is lower than the power of the boiler. Added after 8 [minutes]: It is only small, but when choosing a boiler with a minimum power of 3-4kW, we can choose a single-function or double-function boiler. If we want the minimum power to be as low as possible, we can choose between 2-3kW, but then only single-function boilers are available. A single-function boiler requires a domestic hot water tank, which takes up additional space, so it may be crucial in an apartment. But since you are writing about a Junkers Smar 5C boiler with a power of 24kW, you have a 1-function boiler, because a 2-function boiler has 20kW for central heating and 28kW for domestic hot water. In such a system, you could have purchased the ZSB14-5C model, i.e. a 14kW boiler with a minimum output of 2.3kW for 40/30, and in your case such a boiler would be better suited in terms of central heating power. At most, you can also select the power based on your hot water needs if someone has an exceptionally high demand, e.g. because they like to use the rain shower for half an hour non-stop.

rustin · Answer

I checked, I set the set temperature in the house at 22` to 23`, after a while the boiler started up with 47% power and immediately it started to drop to 13%. Does it make sense to limit it in my case?

rustin · Answer

Can anyone advise whether to limit it or not?

bumble · Answer

You`re supposed to do that. 75% for starters. You`ll see what it will be like in heavy frosts. If you limit it and there is a demand for the full power of the boiler, you may not be able to heat it, but in your case this is unlikely.

Added after 36 [seconds]:

How do you know that the boiler started at 47% power?

Added after 2 [minutes]:

You will have the power reading in the service data. When starting up as you described, did the boiler start with the maximum fan speed? If so, it means with maximum power. I don`t really know what the burner power is 47% and the boiler power is 24Kw. Is your boiler a single-function zsb?

Added after 6 [minutes]:

What is the power requirement of the house? What house? Additionally, it offers the intelligent Drayton wiser heating and control system

Added after 39 [seconds]:

https://www.elektroda.pl/rtvforum/topic3620638.html

Added after 34 [seconds]:

Then you won`t have to worry about the limitation because the boiler will fire up when needed.

BUCKS · Answer

since you have the original CW400 regulator, which communicates with the boiler and controls its boiler power, in my opinion, changing the maximum power settings in the boiler will probably not affect the operation of the boiler. Setting the maximum power would be important with a regular ON/OFF regulator, because then the regulator does not change or control the boiler parameters and the entire heating process takes place only according to the settings on the boiler. As a rule, you can set the maximum power that will be needed for frosts to -20. For example, if you have an uninsulated building and you need 100W/m2, then if you have 100m2 you will need a maximum of 10kW for frosts of -20, not 24kW for

rustin · Answer

Bumble, I see you know less about yourself than I do. So I don`t know if there`s any point in having discussions with you.
Are you seriously asking how I know how fast the boiler started? Since I posted a photo, you can probably see for yourself. I was standing at the controller, the boiler was not heating, I increased the room temperature and immediately entered the cw400 service mode, there was no flame, the fuel valve was closed, the actual burner power was 0%. After a while, the boiler started, the burner started and the burner power started to increase, it reached 47% and after a while it started to decrease. The boiler has a power of 24 kW. So 47%, let it be about 12kW, with this power it started. Then you ask how I know what time it started?

Bucks is probably, as you say, zd cw400 controls the power of the boiler, which can be seen during its operation, when the burner turns on if there is a demand for heat.

bumble · Answer

So tell me, what is the nominal power of 24KW? If the burner power is 12 kW, what is the rest?

Added after 50 [seconds]:

Everyone advises you to lower the boiler because it is oversized, and yet again you ask whether to lower it.

Added after 56 [seconds]:

You did not specify the type of boiler. We know what kind of boiler it is from Cerapur and 24KW

Added after 6 [minutes]:

Lower the power to 50% and start the boiler. Let`s see if it will still fire at full burner power? I think I can`t be wrong. This is how you can save on gas, especially when the boiler is running. Every firing. Burner on max then on minimum and why? Maybe 30% will be enough for you.

BUCKS · Answer

CW400 shows what can be read from the boiler, so it is reliable data. 24kW is the nominal power, i.e. the maximum power of this boiler. The minimum is 12%, but you have to approach these percentages with caution, because 12% of 24 is 2.88, and the ZSB24-5C model has a minimum of 3.0kW for 80/60 boiler water, so this 12% is not entirely clear what it comes from is counted. This 47% is the actual power of the burner at a given moment, but looking at the discrepancies for 12%, it is difficult to say exactly how much 47% is. I estimate that it is over 12kW. Although mathematically 47% of 24 is 11.28. Starting power is another parameter, which, as I recall, was most often around 6kW, so the 47% does not have to be starting power. These parameters can be set and read on the boiler, but I do not know if the service menu is fully available if we have a CW400 regulator connected. If the boiler starts operating at a level of approximately 12kW and then modulates down, then if we limit the power to 10kW, the boiler will start at a maximum of 10kW and then modulate down, unless the regulator settings have a higher priority than the boiler settings. not probably, but definitely, because CW400 type regulators are bought to make the boiler control more sophisticated, not just simple ON/OFF. You`d have to read the CW400 manual to see what you can change, and then there`s a series of tests to see what the difference will be in practice. On the one hand, it gives many settings options, which may be terrifying for a layman, but on the other hand, it gives you the opportunity to set everything to best suit the user`s individual needs.

bumble · Answer

As I mentioned, I have a zab14 with fw100. From what I remember and tried, the boiler settings are priority. It`s not about temperatures. Maybe someone can explain this to me. The boiler has 24 kW and the burner has 47% of what? Power is given in watts, not %. And if so, if the burner has 12 kW, where does 12 kW come from? My boiler has two power settings for central heating and domestic hot water.

Added after 2 [minutes]:

http://junkers-pl.boschtt-documents.com/download/pdf/file/6720860036.pdf
Technical data at the bottom
Rated power 24 at 80/60, minimum over 5kW.

rustin · Answer

Bumble, I don`t know what not to understand here, Bucks wrote exactly. Maybe he`ll want to fight it again. Like the bull writes in the first post what kind of boiler and you don`t provide any photos. Do you read at all? Junkers cerapur Smart 5C 24kW, can you take a photo again? No offense really, but you have no idea, you are just repeating what you read and not reading exactly what is written

Cw400 has priority over the boiler.

Bucks, then there is no point in messing with power in my case, if I understood your post correctly

bumble · Answer

Someone put a nonsense sticker saying the burner power was 47%, which had nothing to do with anything. Cw has priority not in all parameters. Although I don`t know because I have fw100. You started a topic wanting an answer and you got it. Most boilers ignite at max power. If you limit it, you will save. But I have no idea. Probably not. But I didn`t buy the oversized cauldron for myself. When it comes to savings, read the topic from the link I provided, maybe you will like it. Besides, I don`t know anything. I just wanted to know what this 47% is. Because if the burner in the boiler has 12 kW, how does the boiler have 24 kW? Bucks didn`t explain this. Have you read the pdf? Parameters. There is no word there. Anyway, it`s not important now.

Added after 32 [minutes]:

Rated power 24 at 80/60 degrees Celsius, efficiency at this temperature (no condensation according to technical data: 96%. 24*0.96=25kW. The burner should have this power for the boiler to obtain its rated power as the only source of energy in the boiler. Unless that there is something else. These powers will be higher at lower temperatures, as stated by the manufacturer - 106 degrees Celsius.

rustin · Answer

Man, I have floor mats, it says in the first post. so there was something wrong with 80/60 degrees Celsius. I`m ending discussions with you because it makes no sense

bumble · Answer

Read with understanding. The 80/60 parameter is for a boiler power of 24kW. For 50/30, the boiler power is 25kW. 80/60 doesn`t bother the floor fan because you probably have a mixer with a pump and a valve, or maybe it`s a fluke. I claim that for a boiler power of 24kW, the maximum burner power is 24kW, full stop, and it cannot be otherwise. The burner is modulated, so power ranges from 4 to 24 kW. Physics. 24kW does not come from the moon. I`m also finishing the discussions and to understand it you have to go back to primary school. The burner power must be greater than the boiler power because there are still losses. I suggest reading, in your case, man, a long read. Answer my question: if the burner in the boiler has 12 kW, where does the boiler have 24 kW???

rustin · Answer

Who told you that the boiler has a 12kW burner? Who told you the wisdom that you need a mixer just for the floor? Get over yourself and don`t get carried away anymore

bumble · Answer

You, my friend, are probably making fun of yourself here. Added after 33 : Added after 50 : Added after 1 [minute]:

rustin · Answer

Let Bucks explain it to you if you don`t understand what he wrote
Assuming that you only have underfloor heating at home, like me, and 0 radiators, you should congratulate the master who provided the mixer.

bumble · Answer

Go on with yours. Great. Congratulate. That`s it. Limit. Don`t limit yourself. Do what you want.

Wojewoda82 · Answer

The percentage given by the display regarding the current burner power varies from manufacturer to manufacturer. I have a 24KW boiler for hot water and a 20kW for central heating, turned to 10kW for central heating and, for example, for central heating it shows 70% a moment after starting, although it is turned to half of the nominal power. When it goes down to minimum power (5.2KW), it shows 0%. So in my case it shows a little differently. MCR HOME 20/24.. With a maximum power of 10KW it has 100%. I haven`t checked the DHW, but it probably calculates differently there because it has a larger operating range (it`s hard to get more than 30% with the battery open at full capacity and the water at 38 degrees).

So either the % on the display (of the boiler or the controller) means % of the nominal power (then it will not go to zero when the burner is on) or % of the available burner modulation (it will go to zero). I guess that`s how you have to explain it.

Now I turned it on specifically for central heating, the boiler fired up at about 70% of the available modulation, i.e. somewhere around 8KW, dropped down to 10% for a moment (i.e. somewhere around 5.5KW) and then spun up to 100%, i.e. 10KW. It took him a total of 20 seconds. So @bumble, your theory that the boiler always starts with max power is a bit off... In many boilers, the max power is limited and the starting power automatically drops to the limited max power (if it was higher). In others, there is a separate regulation of the starting power.

In my instructions for the installer there is a Fan RPM start parameter (i.e. fan speed, and therefore starting power), which can be changed, page 33:
https://dedietrich.pl/wp-content/uploads/2016/09/MCR_Home_IT.pdf

[Solved] What is the power limit in the Junkers Cerapur Smart 5C 24kW boiler?

Post #1

Post #2

Post #3

Post #4

Post #5

Post #6

Post #7

Post #8

Post #9

Post #10

Post #11

Post #12

Post #13

Post #14

Post #15

Post #16

Post #17

Post #18

Post #19

Post #20

Post #21

Post #22

Post #23

Post #24

Post #25

Post #26

Post #27

Post #28

Post #29

Post #30

Topic summary