VCW Sine 18 T3

[al-yeti]

So now that i found a real plumber to open up the combustion chamber,


I realise why my question wasnt being answered, not all corgi plumbers know what a venturi is and how it works, guess not all of you did the physics of it.

Never mind, i getting a new one as the plumber previously either damaged or removed it, so this would give the diff valve a problem.


Just thought you would like to know.

 

[DP]

al-yeti, not a very friendly post in light of thread sitting on page 4. Perhaps you do not know that many heating engineers who post here, as a matter of course clean the item you say they know nothing about.

How do you know that the venturi on your boiler was damaged or removed. WHY NOT worn out. How do you know the pump is not weak, thus not generating enough differential pressures?

Venturi in the T3 model sit atop the top connection on the pump. It can either be removed by removing the pump (quite difficult) or removing the heat exchanger. While the heat exchanger is out, it can be cleaned.

 

[al-yeti]

I know becuase the heating engineer showed me, you didnt see the unfriendly post made earlier to Agile by an engineer on this site, as i think its been deleted,

PS pump has been checked and done already.



Regards
Yeti

 

[Agile]

Since the water venturi is not that easy to remove its difficult to immagine how any engineer could have "damaged or removed it" or why they would even want to do so.

We dont normally need to touch it because any failure of the system flow switch is usually caused by air, a faulty or blocked pump or a blockage elsewhere in the boiler.

If the pump appears to be working correctly and is clean and there is no air then I would chemically clean the boiler. That would deal with any blockage where ever it might be.

Tony

 

[DP]

Tony I would disagree with your last post as venturi does wear out. Who knows at what rate the orifice will erode in presence of solids like black sludge and sediment.

To say a pump has been checked. How did you check the pump? Could you enlighten the uninitiated as I am not aware of a foolproof method that will beyond doubt indicate the pump is slow (i.e. low RPMs). To say the rotor will resist gentle pressure. My shovel like hands will certainly not be able to apply the same pressure as another person elsewhere who has nimble fingures.

 

[al-yeti]

Hmmm how was the pump tested, you know i dont know how the engineer did it as i aint the expert, but as for fingers it wont stop with them infact you cant stop the pump by trying to force it to stop......

So how else can a pump be tested , as you are correct, it could work but be slow , doesnt seem slow to me tho!



So if you are correct and the venturi is fine, the pump is running (what is low rpms'... difficult to test obviously)


what next then....... chemically clean the boiler? doesnt make sense to me as you referred to the flow switch.

Unless you are saying the blockage could be in the flow switch , causing the differential prerssure to drop.


Yeti

 

[Agile]

I have often needed to clean the boiler chemically as a result of a blockage somewhere.

Rather than dismantle everything which would take a whole day its much faster to chemical clean and that takes care of multiple blockages in different places.

I have never inspected the venturi closely but have always assumed its a brass restriction which is aided by the entry angle of the connections. If thats the case I would doubt there is much likelyhood of a serious erosion of the brass during normal usage.

Rather than carry on talking and trying to argue for not doing anything why not chemically clean it and see what is the result. As you have said the pump is fine and neither pressure switch tube is blocked then as I see it there can only be a blockage restricting the flow.

Tony

 

[al-yeti]

oh ok , what chemical do you suggest , and do you mean to run it through with heating on???



Yeti

 

[Agile]

No, boiler only using citric acid, DS40.

Repeat several times until there is little black coming out when you drain between each application. The Sine 18 is very convenient with the little drain nipples you can put a tube onto.

Easiest to introduce the solution through the AAV. Run boiler in DHW cold at first and then warm it up after a few minutes to about 60 C. About 10 minutes per cycle.

If there is much lime compound you may need to do a cycle or two with sulphamic acid, DS3. You have to dissolve that in boiling water and can run it in the boiler up to 85 C as it has little effect when cool. Use DS40 first though.

Tony

 

[al-yeti]

ok boiler seems to be fireing up more than before , but still not quite there, there still isnt enough differential pressure to keep that gas pin in as you can press, the pin in on the diff valve easily with no pressure when pump is running, this should not be possible.


So i must be doing something slightly wrong as i agree Tony that there is obviously some kind of blockage or something stopping circulation.


I wonder even tho the flow switch is showing operation between demand of DHW and CH could this still cause a significant problem in the boiler circulation itself?

Could you explain when running the DHW from cold first how this affects trying to unblock the system, is the inner parts of the flow switch which could have poor circulation or debris being moved about.

Hence why from refilling system , with sudden pressure boiler fires first time , but once pressuried boiler goes back to its issue of low diff pressure, making me think once water is in one of the components it moves the debris into a postion to stop good circulation.


Regards
Yeti

 

[Agile]

ok boiler seems to be fireing up more than before , but still not quite there, there still isnt enough differential pressure to keep that gas pin in as you can press, the pin in on the diff valve easily with no pressure when pump is running, this should not be possible.

Regards
Yeti

Have you cleaned it as I suggested?

Exactly what did you do?

What was the effluent like?

Tony

 

[al-yeti]

Yes, effluent?

 

[DP]

What has someone saying saying something to someone else got to do with problem on your boiler?

The pump causes positive and negative preassure to be generated in the two pipes connected to the venturi. This unequal pressure causes the flow switch spindle to eject to allow gas to enter the mainfold below the second stage of the gas valve.

If the pump was running slow, venturi is worn out, boiler pipes are encrusted and flow effected, heat exchangers partially blocked, you will have similar problems. Burners may fire from cold but as water heats up, water that is now not as dense, may not have sufficient density to keep the gas valve open (spring in gas valve is quite strong).

 

[al-yeti]

Pump running slow? cant stop it by hand or finger , does this mean its fine or not? there is no sludge in pump area or in venturi , infact venturi is new.

 

[al-yeti]

Question , apart from everything else being checked can the main expansion vessel cause loss of differential pressure??? as it is connected to the same circuit or is that just when water expands.