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If you remove the cover on a lot of modern Boilers, you disturb the seal that makes the appliance 'room sealed' as has previously been said.
Room sealed means it is fairly well sealed from the room the appliance is situated in. The appliance draws air for combustion from outside.
Due to the volume of air that can be pulled down the air intake section of the flue pipe the appliance will burn differently with the case off than it will with the case on. When the case is on, there is a slightly negative pressure inside as only a measured amount of air can enter the appliance. Without the case there is more air available because there is less restriction. That alters the pressure inside the appliance and in turn this alters the products of combustion from the appliance.
The reason you are supposed to be Gas Safe Registered is because you are supposed to be considered 'competent' in testing how the appliance is performing after it has been worked on, meaning that you 'know' it was left burning safe.
On most modern Boilers the seal is also the insulating material inside the front cover.

Hope that reads right and makes sense!
Hi, I'm a little confused by this.
I apologize in advance for my ignorance, I'm competent at general plumbing but not gas trained in any way so please bear with me.
Most of the boilers I electrically connect up (mainly combi ones) the front access cover is just hooked on a couple of pins at the top and held back by a couple of screws at the bottom. I haven't come across any type of seal in these instances. This cover just appears to be a shield rather than an integral part of the boiler? in fact the boiler is open to the room from underneath anyhow even when the cover is in place and I have often come across boilers with this cover left off (not good practice I know but no one seemed over concerned about it).
I certainly wouldn't even attempt to remover a cover that was clearly part of a sealed chamber.
 
Next time you look just have a gander to where the air intake is for the burner. The air for combustion often comes in via the outer part of the flue, then into this chamber (which is basically where most of the plumbing bits are) and into the air intake. Unless there is a seal it cannot be deemed "room sealed"
It is not always obvious as it is just like a draught excluder type strip of foam .
cheers
 
Next time you look just have a gander to where the air intake is for the burner. The air for combustion often comes in via the outer part of the flue, then into this chamber (which is basically where most of the plumbing bits are) and into the air intake. Unless there is a seal it cannot be deemed "room sealed"
It is not always obvious as it is just like a draught excluder type strip of foam .
cheers
Right, I will thanks for that. Nice to learn something new!

So what are is the reason for relying on the air intake from outside rather than from the room?

Since the air intake is in close proximity to the fume outlet is there a chance that fumes can be drawn back in, thus if the cover is off there is a possibility that some may escape back into the room?

Is this why modern boilers can now be more enclosed in cupboards and such?
Thanks again for the info I'm always keen to learn and get an understanding of things.
 
Hello.
in fact the boiler is open to the room from underneath anyhow even when the cover is in place
If you look at it, it does appear to be open but in fact there is a base to the section that houses the heat exchanger, burner etc. The front case comes down below that by around a third again. The base area (where the pipework beneath the boiler and PCB, wiring box etc are), is open but the section I am talking about (room sealed bit) is above all that. Inside the front case there is a cushioned sponge seal that acts as insulation too. This will seal the top box from the room once it is in place. In this, I am talking about most modern condensing type Boilers. older Boilers or some commercial are different again.
So what are is the reason for relying on the air intake from outside rather than from the room?
You need 2 volumes of Oxygen to burn one volume of Methane (CH4). As the air we breath contains Oxygen at around 20.9% , we need to use around 10 volumes of air to each volume of Gas we want to burn. An average 30 Kw Combi for example will use approx 3.2 M cubed of Gas per hour, therefore it will require 32 M cubed of 'air', to provide the (roughly), 6.4 M cubed of Oxygen the Burner requires to completely burn the Gas. If we bring the air in from the room, we obviously need to install an air vent like we do with some open flue appliances or some flue-less appliance. Room sealed are a better design due to them having a means of providing combustion air that is more measured, permanently there, smaller, less draughty, no need for Mrs Goggins to block it up with a copy of the mirror, no risk of Mr conservatory removing it and leaving the appliance unsafe, less risk of spiders blocking it with webs and food etc etc.....all round much safer, more comfortable less reliant on tradesmen to install it and inspect it.
Since the air intake is in close proximity to the fume outlet is there a chance that fumes can be drawn back in, thus if the cover is off there is a possibility that some may escape back into the room?
Not much. The flue is designed if you look at it to have the exhaust further out than the intake. The Burner fan or flue fan will push flue gas away under pressure into the atmosphere where it dissipates.

They are kept fairly separate and the pressures are balanced, hence the name, balanced flue. If you left the case off and the appliance running then there would be a chance/possibility of products of combustion entering the room yes. You have removed the balanced design aspect by breaking the seal.
Is this why modern boilers can now be more enclosed in cupboards and such?
We have always been able to install wall mounted Boilers in cupboards as long as they'd fit in one that is. Most older types needed ventilation though. For two reasons, one for combustion air if they were open flue appliances and the other for cooling. Modern Boilers in plant rooms still need cooling ventilation where necessary due to the Electronics and electrical controls inside them. There are MAX temperatures to be observed in places like this.

Sorry for the massive post. I hope it answered your queries.
 
Last edited:
https://www.---------------.co.uk/media/1449/who-can-legally-work-on-a-gas-appliance-factsheet.pdf


The white cover is a decorative cover and has no seal. This is the cover that would usually need to be removed to get to the electrical connections. Therefor no gas safe is required.
Although usually the electrical connections to boilers are an utter pain in the arse and in my opinion are a always badly designed, even the Boiler manufacturers wouldn’t put them behind a sealed case!
 
It's worth noting the law changed on 5 April 2018.
There is a new “Safety in the installation and use of gas systems and appliances”

http://www.hse.gov.uk/pubns/priced/l56.pdf I strongly recommend a read of this, I found it very informative.

The regulation sates “No person shall carry out any work in relation to a gas fitting or gas storage vessel unless he is competent to do so.”

Fortunately, in the new document we now have “ACOP” which is the Approved Code of Practice. This is not law, but it does state; “Gas work should only be undertaken by a person who has successfully completed an industry-recognised training course followed by assessment of competence”

It also mentions “the code has a special legal status. If you are prosecuted for breach of health and safety law, and it is proved that you did not follow the relevant provisions of the code, you will need to show that you have complied with the law in some other way or the court will find you at fault”

Previously I would argue I am competent. However, going forward I think I would struggle to win this argument as the new policy coming into force now closes that door firmly shut by giving guidance on what they deem competent. There are no longer any grey areas.

In conclusion you must not work on any gas fittings unless you have proved your competence by means of an assessment. This now very explicitly also covers your own boiler. No more DIY.
However, I have not seen anything that prevents a "competent" person replacing the pump or pcb etc. As a qualified spark you could easily prove your competence in this area.
To confirm "gas fitting" includes all inlet and outlets for the gas.
 
I would have thought that if the casing is acting as a plenum chamber, there would be some form of safety switch preventing the boiler from running with the cover removed?
 
Recently we purchased a new range style cooker. Electric oven & gas hobs. I went for the installation service, 'cos they took away the old en. The installer said he was gas safe registered, and was until recently 'Part P' registered (I didn't enquire what that entailed), but he had no electrical qualification apparently.

The gas connection was via flexible hose, which required testing (does it have to be done by gas safe bod?) which he did. The electrical connection was done by him, & tested (Zs).

So he could connect the gas bit 'cos he is registered, but could connect the electrical bit with no such qualification or similar registration?
 
The white cover is a decorative cover and has no seal. This is the cover that would usually need to be removed to get to the electrical connections. Therefor no gas safe is required.
Although usually the electrical connections to boilers are an utter pain in the arse and in my opinion are a always badly designed, even the Boiler manufacturers wouldn’t put them behind a sealed case!

wrong the only time you can remove the front cover / decorative cover is when there are no fixings to hold it in for example no screws clips pins etc

thats why most boilers come pre wired
 
depends if the
penny pinching landlords is an example.
that's already illegal though under GSIUR, as it's for reward (you're receiving rent for the place)

I would have thought that if the casing is acting as a plenum chamber, there would be some form of safety switch preventing the boiler from running with the cover removed?
could, but for some testing e.g. working pressure the boiler must be operated without the cover fitted for short periods. This is deemed acceptable.
 
As far as I am aware all modern boilers have a safety switch which prevents ignition if the fan is either not running or not providing sufficient air flow.
This safety switch operates by means of a diaphragm.
One side of the diaphragm has to be situated where there is normal atmospheric pressure, somewhere it is unlikely to be blocked or subjected to a vacuum.
If the cover is sealed, the end of a tube will poke out through the casing.
If the cover is not sealed the end of the tube (if there is one) will be inside the casing.
 

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