Condensation inside Gas Condensing Boiler

[Thomas0]

Hello everyone,

I have an issue with my gas condensing boiler and so far I didn't find someone who was able to found out the issue...
It's a Saunier Duval Thema Plus Condens, a french model that is 9 years old.

The problem is that some condensation appears inside the boiler after use. It can take up to 12 hours for it to appear on cold elements like the back or front panel (which are in metal).
Since I have the issue I'm leaving the front panel open to keep the condensation from coming but I know that it is wrong.
Plumbers that came to check thought the water was coming from the air intake on top of the boiler, because of a possible leak with the inner fumes exhaust pipe.
One used a probe to measure the composition of the air intake (the front panel was ofc closed). No CO was found and O2 was at 20.9% which seems to indicate that no fumes were leaking into the air intake pipe. The pipe was also unmount and no water was found in the outer section (see attached photo).
Also, the condensate drain was tested and no problem was noticed.

After more investigations I found out water in the air entry before the gaz mecanism and the extracting fan. The air was humid and warm, even hours after use of the boiler (I only use it to get hot water for showers). The water was found inside the black tube where I added a blue arrow in the attached photo.
I have measured very high levels of humidity in that tube (90% RH) and high temperature (30°C when the room is at 18°C).
Also there is a smell of gas coming out from that black tube just after the boiler shuts down. Sometimes some CO (up to 60ppm) come out from the tube, also just after shut down, and then nothing but humidity. One plumber told me it was normal as some unburned gas could leave the combustion chamber after the fan stops. Moreover, I wasn't supposed to smell it because the front pannel should be closed.

Could you help me with that issue ? Could you confirm that it's not normal that some moisture come out from the blue arrow ?
When the fan stops, is there some mecanism that should prevent moisture to come out ?

I thought that maybe the fumes we not evacuating correctly and stagnating inside the combustion chamber before eventually leaking. But I can see fumes leaving at the end of the flues.

Thank you very much in advance.
Best regards,

T.

 

[kidgreen61]

Hideous boiler, skip it.

 

[Madrab]

I hope this is a wind up ... that boiler is now classed as dangerous if it's being run with the room sealed case off of it. For your and yours safety, please get the case front back on it. Stop pulling the flue apart too, it can really be quite dangerous.

It is quite normal for condensation to be found there and in the flue, it is a condensing boiler after all.

 

[Thomas0]

I hope this is a wind up ... that boiler is now classed as dangerous if it's being run with the room sealed case off of it. For your and yours safety, please get the case front back on it. Stop pulling the flue apart too, it can really be quite dangerous.

It is quite normal for condensation to be found there and in the flue, it is a condensing boiler after all.

Thank you for your answer.
I'm leaving the front panel opened after use and only a professional has operating the flue.

If I don't open the front panel, the condensation inside will become more and more significant and leak from the bottom of the boiler after some days (small drops of water but still not normal, right ?). Moreover, water may damage the electronics.
I've only had this condensation problem recently, the boiler worked well for 8 years.

Best regards,
T.

 

[Madrab]

OK, only a qualified gas professional should be removing the front case here in the UK, not sure of the regulations in France though.

Condensation can only be created by either moist air being drawn in or the products of combustion and it's condensing as it enters the air intake and is being compressed slightly, so the boiler must be drawing in either the combustion gasses ( gas operative can test for this) or the air that supplies it must be quite damp air, only way really that it can happen.

Condensation in the flue is normal, that's how a condensing boiler would operate.

 

[Thomas0]

OK, only a qualified gas professional should be removing the front case here in the UK, not sure of the regulations in France though.

To be honest I don't know but I wouldn't take the risk to touch it myself.

Condensation can only be created by either moist air being drawn in or the products of combustion and it's condensing as it enters the air intake and is being compressed slightly, so the boiler must be drawing in either the combustion gasses ( gas operative can test for this) or the air that supplies it must be quite damp air, only way really that it can happen.

I'm pretty sure this is not the damp air because it always happen, even if the humidity is low outside (RH 50%). There are also very light black traces on the front panel (like soot?), when I clean it to remove water.
So I would assume the origin of condensation is combustion gasses. The weird thing is that plumbers / gas operatives did look for CO outside (near the flue) and inside the boiler. Nothing was found when the boiler is operating. However there is CO coming out of the silencer (what I was referring as the "black tube" in my first post) few seconds or even minutes after the boiler has stopped. And then condensation appears inside the silencer.

Do you believe it is a problem with the flue, even if combustion gasses would be leaking from the silencer ?
Thanks again

 

[Madrab]

However there is CO coming out of the silencer

As the air intake (silencer) is directly connected to the combustion chamber (CC) through the burner and then fan, then it's conceivable that air is being drawn in through the flue and then through and drawn out through the air intake. That would need a pressure differential between the flue and the case allowing some 'reverse' circulation of air back down the flue, through the CC , past the fan and out the silencer.

1 good reason why not to keep the room sealed case off the boiler, if CO is emerging from the silencer therefore it's getting into the room

 

[Thomas0]

So there is a depression in the case ? Could it also be the flue that is partially clogged ?