Boiler cases and room seals

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I hope this is not straying into CC territory, but I am confused.

In another topic someone wrote:

As far as i know doesn't the case that provides the room seal for this model have to be removed to get to the electrics, not really diy territory.

The boiler in question is a condensing boiler which gets its oxygen supply via the external air intake and discharges the products of combustion via the flue to the outside. So why does the case need sealing?
 
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A question for you DH...

Would the removal of front case effect combustion? ..and if your answer is yes then why?
Some boilers use air intake snorkels (trumpets), which can be dislodged easily and hence effecting combustion.
 
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Because the incoming air to a boiler is circulated around all the internal components to cool them and then ejected outside by the fan.

Some earlier boilers even pressurise the case with external air and they are particularly dangerous and need the RGI to carefully test the case seals on reassembly.

Tony
 
You have a positive pressure combustion chamber. If the combustion chamber door seal fails without the external case seal in place then you have the potential of 200ppm of CO spelling into your property. Enough to kill you very quickly.
 
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The definition of room sealed is the air inlet and flue outlet are sealed to the outside.

As soon as you take the cover off the appliance is no longer room sealed. Therefore the case seal forms part of the safety of the gas appliance.

Most of the RGIs on here will have occasionally experienced a high CO reading in the flue outlet, which disappears when the cover to the boiler is removed. There are a variety of potential causes of this, which I am sure, D_H, you can think of (because I sense you have some related knowledge in our industry).

The fact that this can happen is why Gas Safe consider the front cover should only be removed and replaced by qualified people.
 
And in jeff's scenario the 200ppm is only the concentration in the air being expelled from the appliance, this is obviously further diluted in the house.

The danger with the case leaking is that the vitiated (CO corrupted) air is now being supplied to the appliance instead of fresh air. This very very quickly raises the CO concentration to 1000s of parts per million.

And it will keep rising till either the boiler cuts out due to insuffient oxygen or you get your gas cut off.
 
Very interesting, but I don't understand all of it as some things seem contradictory.

Steelmasons: Some boilers use air intake snorkels (trumpets), which can be dislodged easily and hence effecting combustion.

Yes, my boiler has one of those, but I can't see the point of it. The combustion chamber, which is within the heat exchanger, already has an air intake to the outside, so why does it need a second intake via the trumpet? And, as the trumpet is within the "sealed" case, where does it get its air from as the air in the case will eventually run out?


Agile: Because the incoming air to a boiler is circulated around all the internal components to cool them and then ejected outside by the fan.

That implies that the hex/combustion chamber is not sealed, but allows some incoming air to escape into the "sealed" boiler.
Jeff:

So it's a safety device? I can understand that.

Simond: The definition of room sealed is the air inlet and flue outlet are sealed to the outside.

But if the combustion chamber is sealed, apart from the air inlet and flue outlet, the boiler is already room sealed, so the case is superfluous.

That just leaves the safety aspect as the reason for sealing the case.

 
Some band A boilers (premix) will have air supply upstream of fan and hence 'not within combustion chamber" , air snorkel is attached to combustion fan Venturi which is a push fit affair.
Not all premix burners use this arrangement , some of the Worcester brand incorporate air intake/fan/Venturi within combustion chamber so removal of front case is not a problem , Vaillant along with other manufactures use the former arrangement.
Removal of air intake trumpet will effect combustion by around 1% CO2 (gas lean).
One particular model of Worcester is notorious for gasket failure within combustion chamber (cleaning/inspection plate gasket) , when this gasket fails POC are forced out of combustion chamber , with front cover removed copious amounts of CO will be spilling into dwelling.
 
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for us as engineers we also have a duty to test the effectiveness of any case seal under 26(9) when working on an appliance.
 

Yes, my boiler has one of those, but I can't see the point of it. The combustion chamber, which is within the heat exchanger, already has an air intake to the outside, so why does it need a second intake via the trumpet? And, as the trumpet is within the "sealed" case, where does it get its air from as the air in the case will eventually run out?
"Eventually run out"?
Snorkel will draw air via flue intake duct , snorkel will be in the vicinity of intake duct.
Are you saying this is not the case with your Remeha?..:eek::)....oh dear....definitely a situation whereby front case should not be removed , have it checked by a GSR engineer ASAP.:censored:;)
 
Snorkel will draw air via flue intake duct , snorkel will be in the vicinity of intake duct.
I have always assumed that the air intake was a sealed conduit into the combustion chamber, so no air could get into the boiler case from the air intake. But, of course, air needs to mix with the gas before it is ignited, not after. Looking at the part diagrams for my boiler (below), I assume that the air comes down the outer tube of the "flue" and then travels horizontally and enters the boiler case through a second hole in the case top. (I assume this is a left-over from two pipe systems as the system and combi versions do not have this arrangement.

combustion chamber.jpg Air trumpet.jpg
 
The first bit is correct. Your second comment regarding combis etc does not make sense.

Most small domestic gas boilers have a similar concentric flue intake like you show.

Nb: your plastic Avanta is more often used with a two pipe flue in the Netherlands, so the white elongated box on top of the boiler is a concentric adaptor for other markets.
 
Because the incoming air to a boiler is circulated around all the internal components to cool them and then ejected outside by the fan.

Some earlier boilers even pressurise the case with external air and they are particularly dangerous and need the RGI to carefully test the case seals on reassembly.

Tony

Tch!
 
I hope this is not straying into CC territory, but I am confused.

In another topic someone wrote:

As far as i know doesn't the case that provides the room seal for this model have to be removed to get to the electrics, not really diy territory.

The boiler in question is a condensing boiler which gets its oxygen supply via the external air intake and discharges the products of combustion via the flue to the outside. So why does the case need sealing?

Is your stance on this any different now DH?
Would you advocate front case removal.
 

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