EXPLAIN THE SCIENCE BEHIND COMBI BOILER WORKING

I would be most grateful any \\\" Boffin\\\" can explain to me the science behind the Combi boiler so I can understand why my boiler shake.

At present as a layman all I understand is:
Gas supplied through the main.
Electric to run the timer & maybe spark?
Water comes in from the main supply: supply (A) a concealed system of water for the central heating
(B) go through a loop of pipes where the gas fire up when the hot water tap is turn on. This supply the hot water needed.

FLUE: this is for channelling the fumes burnt by the boiler out.

Q1) If you refer to my other query on 19/10/05 where I mentioned my boiler shakes. Please explain to me the science behind the boiler.

Q2) What is the important governing factors?

Q3) Does air circulation in the room where the boiler is affect the performance of the boiler?

Q4) Does water pressure from the main supply affect the boiler? If the stop cock is turned half, will this affect the boiler? Any of this affect the DHW or the CH?

Q5) How does the flue configuration/route affect the boiler?

Q6) Why my boiler shake for 15 seconds then stop?

Q7) Does the gas supply have any effect?

Hope some one will enlighten me.

Thanks

You wouldn't be asking us to answer your exam questions would you?

Hi slippyr4,

What exams?

Just like all problem, a little knowledge is dangerous but greater understanding will help to appreciate what the proffesional are doing and why they have to carry out what they do.

Exams!! these days exams are in open book & no need to revise also can pass because all academic institution wants their puple to pass and they have good pass rate. Other institutionwants you to pass so you canjoin the membership and pay higher rate.

So if I want to pass exams, I do not need to ask and understand. Just talk!!!

"Bragging"??

Specific heat capacity of water (SHC) is 4.2 kJ/kg/K
1 kW = 1 kJ/second
Calorific value of gas approx 38.5 MJ / m3
Efficiency of appliance (varies with model) between 70% and 90%

So now you can see if you burn more gas you get more heat energy, you transfer this into the water so higher water flow (kg/second) gives a lower gain in temperature.

The boiler has controls to limit the size of the flame (to stop it melting itself), and the temperature of the water (to stop it boiling the water).

Will that do

Hi meldrew's_mate,

Wow! what a feet of acamedia storm.

If the boiler is cold, ie the CH is not on and I turn on the kitchen sink hot water tap.

Kkkhankkkkkkk ttttttttttttttttttttttttttttttt tttttttttttttttttttttttt

the boiler shake madly for about 20 seconds.

Do I burn more gas here?
or is it just the same amount of gas it receive from the gas supply pipe?

Does Tranco gas supply have a steady and regulated supply of gas or does it vary?

The question is why does the boiler shake??

So even if the CH is on & the DHW tap is turn on and it does not shake,

Why does it does not shake?


So are you saying that if I turn the supply water flow to slower, I can gain higher gain in temperature. That explained why the supply pressure is important for hotter water. that explain Q4.

But why does the boiler shake?

Thanks

Skan said:

Exams!! these days exams are in open book & no need to revise also can pass because all academic institution wants their puple to pass and they have good pass rate.

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Sorry mate but you are talking *******s
You have obviously never been to college, no revision or work or interest = no pass.

Fair play to you for seeking knowledge on this forum and I hope you learn well but you have the wrong idea about college courses. There was a few in my class that were somewhat lazy and they did not get their qualification.

Skan we aren't a free education service. Read a load of Manufacturers' instructions, then call the manufacturer(s) and ask them about specifics. If your boiler is making a noise it shouldn't, how are we to know what 's causing it? You have goven NO information.

My car makes a funny noise when it starts. It goes off after a bit. What's causing it? See what I mean

Hi ChrisR,

Yes, I understand that you are not free educator.

That is why I asked specific questions regarding specific problem.

I wanted to understand how a boiler work, so I can eliminate those that are irrelevant.

If I do not know, how to monitor the Corgi man?
At the moment, every time I get a trademan so called with membership to institution etc..
what they tell me is correct? If I do not know what is right or wrong, how to know whether he is talking nonsense "Bu** Sh******"

I am no mechanic nor good with car but if there is a funny noise.
1st of all, I would ask is where the noise come from? Is it from the wheel or the engine or the car body?
2. If it is the body,, could it be a loose nut & bolt?

3 If it is from the wheel, could it be a stone stuck in the thread?

4 Otherwise it could be the tyres & the questions go on to eliminate the problem unless you can shortcut to the problem.

I usually like to know more eg whether the different made tyres have different quality & it could be that maybe one maker can produce a tyres that is hard when the tyre is cold , therefore make funny noise but the noise will disappear when the tyres had warmed up.

5 Engine-- well same logic of analysis

This is from a layman approach but I would like to get the feed back from a qualified/experienced mechanic.

hope this explain my approach.

can you help me on my problem? I just want to know how the boiler work whether it is top of the range Valliant or bottom cheap make in Nigeria from dismantle car parts.

Exams,

I recently took eal level two which qualifies one for vertually any electrical work in a home and inspection and testing of own work at the time of doing the work. It was closed book, many exams, don't recall how many seemed like 3 a day over five days.

ALL the others on the course had to resit a number of them and everyone had to work very hard to appropriate the new knowledge. I sailed through and sat all my exams in about 2 to 5 minutes passed first time. I don't say this to brag but to show you how hard corgi exams are.

Corgi exams are open book, but have you seen those books? You're sat in a reference library. Open book is necessary because of the deeply complexed technical nature of the discipline. It is true that you have the books to hand but it is impossible to find everything in there and inpossible to find all things in time. You must know 90% of the stuff and be able to rattle it off quickly, then you stand a chance looking the last 10% up in the time allowed, you will likely still have 2 or 3 questions (out of 80 in one of the exams) you can't find anywhere and you have to guess.

Yes I flew through my Corgi exams also, but let me tell you it is no walk in the park, many people have to go back for more training and resit.

What is a fiddle is the specialised subjects, on that I agree with you, it's corrupt and inadequate, and pointless.

Hi Bahco from Wolverhampton,

Glad that we have a healthy response.
Did you graduated from Wolverhampton University and major in which subject?

Presumably you got a 1st then?

What grades do you required to get into the University & course you major in?

Is it college or university you attended?
How do you know have not passed? Assuming again!!
Do you belongs to any professional institution?

I understand you bound to defend your territory otherwise it will be a total waste of time & not worth the paper it is written on.

Don't tell me you did not spend nights after nights down at the student Union bars pouring down pints & pints of watered beers at ridiculously cheap price.

If you haven't then you have wasted your chance in your late youth.
If you had, you must be the only one that put so much effort in & is it any different from the guy or gal who seems to prop up the Union bar?

Seeking knowledge or continuous education or CPD?
Or is it badge as life long learning now.

You are basing a a very small sample & as statician will tell you, it is highly inaccurate using small sample. Let say there are 50 in your course and 5 of them are lazy & therefore failed. Can you work out the percentages?
Can you confirm what is the number of intake in the whole year for your college?
Work out the percentages now.

I am glad that this forum also included some high calibre people & degree holder.


Thanks

Hi Skan,

Ignore these grumpy old farts, I'll attempt to explain the theory (though its a little involved so stick with it).

Tell your tutor the following ...

Boiler theory is based primarily around gas and fluid dynamics using bernoulli's theorems of velocity, gravity and pressure. This principle is encapsulated in the bernoulli equation ...

p+1/2pv2+pgh=constant

Where p is pressure, v is velocity, p is density, h is height and g = gravitational acceleration.

Now, as you probably already know, gravitational acceleration is a factor of the gravitational constant of the universe (0.34) multiplied by the totals of the gravitational constants of heavenly bodies within the sphere of influence (in this case, the Earth and the Moon).

This equation also explains the tides by the way as the Moon travels around the Earth it's spatial relationship between the equatorial boundaries causes miniscule variations to it's gravitational constant which creates pressure differences in our seas ... Water flows from high to low pressure and hence the movement of the water we know as tides.

Q2) What is the important governing factors?

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These are the governing factors you asked about, gas and water in the pipes and air in the room are all governed by the same principle and as parts of the above equation change you experience the symptoms you have described.

Q3) Does air circulation in the room where the boiler is affect the performance of the boiler?

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Indeed it does, as the air moves around the room it has a velocity and a pressure which are inversely proportional (i.e. as one goes up, the other goes down). If the air pressure in the room is high the boiler cannot get enough air in from outside and the gas to air intermix ratio is poor resulting in less heat per cubic foot of gas.

Q4) Does water pressure from the main supply affect the boiler? If the stop cock is turned half, will this affect the boiler? Any of this affect the DHW or the CH?

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Yes, increased water pressure reduces its velocity which means the boilers pump must work harder to circulate the water throughout the system.

Q5) How does the flue configuration/route affect the boiler?

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Height of the flue is covered by h in the equation, the higher the flue the greater the efficiency, this is why large organisations such as hospitals (with massive boilers) have chimney flues over 60 feet high. The more air which is presented to the boiler the better (more air + more gas for the same intermix ratio = increased BTU's).

Q6) Why my boiler shake for 15 seconds then stop?

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This can be a combination of many things (which is why the boiler is named combi incidentally). Main factors are velocity of the incoming water supply (note ... not pressure), air movements within the room as previously explained and, most importantly, the position of the Moon's lunar orbit. You should notice that the shaking will be far more pronounced when the moon is at its highest orbit and full Moon's are notorious for causing boiler shake.

Hope this has been of some help.

Please post back and let us all know how you got on.

quite simple really cold water goes in and hot water comes out not to complicated is it .

Skan

Why not just go on a plumbing course? I'm sure it will be a walk in the park for you.

Your queries are advanced stuff and you will need to study hard to satisfy your inquistive mind.

Part P question next week

On a more serious note, make sure the pipes are all bracketed to British Standards, that the boiler doesn't require descaling and system powerflushing, make sure the fan isn't out of balance.