Flue Integrity Test.

[chrisnchris]

Hello, I'm after a bit of advice.
If you, as a gas engineer, needed to "fault find" on a boiler that has a problem, would you do a flue integrity test as one of the first ports of call.
The boiler ignites, stays lit for 20 seconds or so then shuts off. About 20 seconds later, the boiler re-ignites. This process is repeated throughout the boilers programmed time.
Constant on and off.
Just to provide a bit more background. This problem has persisted since September. It was finally resolved in December on the seventh visit by 3 different engineers.
The problem was a damaged clip inside the flue resulting in CO2 ? being drawn into the combustion chamber.

I would have thought that any reported fault on a gas boiler would start off with a test to measure any CO2 leakage.
I would appreciate someone putting me right about this.
Thanks for your input.

 

[Deleted member 120897]

Every job might start off differently, as a gas enginee, I would ask a line of questioning and decide where to go from there.

 

[ShaunCorbs]

Baxi boiler ?

 

[chrisnchris]

Baxi, yes System 36/60
The fault was described by me as "radiators not getting hot and boiler starts then cuts out, then fires up again...etc.etc."
The starting point from the first 2 technicians was "where's the pump?" They couldn't find it and left...
After the first 2 visits I found the pump myself from looking at the main diagram.
Technician number 3 turns up and asks...where's the pump...my reply was polite and to the point..."I think you'll find it inside the boiler"

So, the 3 technicians who came to rectify the fault seemed to think the fault was with the pump. Despite the fact that the problem was obviously within the combustion cycle, it was after all, coming on and going off...constantly.

My question remains, given the extra information, would you have done a Flue test?

 

[Deleted member 120897]

Not from that description no, but I would probably need to be on site to establish what was happing with the combustion process, and whether it would work under different conditions.

 

[ShaunCorbs]

I would suspect pump from the start as it’s sounds like overheating until further investigation

 

[Chuck]

So, the 3 technicians who came to rectify the fault seemed to think the fault was with the pump. Despite the fact that the problem was obviously within the combustion cycle, it was after all, coming on and going off...constantly.

In my experience, the symptoms you describe are more commonly due to a failing pump than the type of flue fault that it turned out to be eventually in your case.

The aim of fault finding is to find faults as quickly (i.e. cheaply) as possible. In practice this usually means perform quick and simple tests that detect or rule out common problems first.

If you want certainty, use the manufacturer's 'fixed price repair' service. It'll be more costly on average but will avoid getting stung if something unusual or tricky afflicts your boiler.

 

[chrisnchris]

Hmmm...pump...none of them even knew where it was, let alone thought about trying to locate it. It's inside the boiler for f**** sake. I think I should point out at this stage that none of them were blind.
The first two suggested I should start to rip out various sections of boxing, the second even suggested ripping up flooring in and around the airing cupboard!!
I told technician number 3 where the pump was.
There was nothing wrong with the pump, he left, the fault remained...

 

[Chuck]

Hmmm...pump...none of them even knew where it was, let alone thought about trying to locate it. It's inside the boiler for f**** sake. I think I should point out at this stage that none of them were blind.
The first two suggested I should start to rip out various sections of boxing, the second even suggested ripping up flooring in and around the airing cupboard!!
I told technician number 3 where the pump was.
There was nothing wrong with the pump, he left, the fault remained...

You were unlucky and have our sympathy but the problem is now fixed so it's time to move on.

 

[chrisnchris]

Thanks Chuck, I guess you're right.
This still grates though.
We're constantly being reminded about the dangers of CO2 poisoning. Everything is covered by a multitude of ever increasing levels of regulations. We can hardly move without incurring the wrath of some kind of enforcement officer.
Yet, when it does go wrong, the powers that be, seem to be ready to jump to the defense of incompetence.
The boiler was actually shut down and capped off in December "Because it was dangerous"

If it was "dangerous" in December, it was dangerous in September when the fault was first reported.
How many possible diagnoses can there be for "combustion to take place, from cold, and continually shut down in roughly 20 second cycles?" (a supplementary but entirely serious question)

This was the reason our radiators never got hot. There was never any continuous heating going on. Like trying to heat a room by striking one match at a time.
How often does a boiler get tested for the integrity of its ventilation system? (or whatever the dangerous bits are called) Once when commissioned? Once every ten years? Once every service?
I mean, apart from the electrical components or the damn thing actually falling off the wall and crushing you, what else is dangerous except the combustion process.

Ergo, if there is a fault within the combustion process, I don't want to go through it again, light, shut down, light, shut down, light, shut down... Ad infinitum ...how can it be not sensible to test the combustion process...from beginning to end...
I'm genuinely at a loss as to why this didn't happen. But then again, I'm not a gas technician.
It's all witchcraft I tell'ee.

 

[Deleted member 120897]

In my experience, people seem to be confusing CO (Carbon Monoxide) and CO2 (Carbon Dioxide).

Thanks Chuck, I guess you're right.
This still grates though.
We're constantly being reminded about the dangers of CO2 poisoning.

I’ve also had evident leaking flues pass an integrity test.

 

[Scott_D]

If it will only stay lit for 20 seconds it’s not long enough to perform a flue integrity test.

 

[chrisnchris]

If it will only stay lit for 20 seconds it’s not long enough to perform a flue integrity test.

Ah, OK, so the boilers own sensor within the combustion process (forgive the lack of knowledge) was able to detect the CO2 being sucked back into the combustion chamber from the compromised flue (again, I don't know what I'm talking about) and instigate a "shut down"
When it detected that the air was clean, the CO2 had dispersed (again, don't know etc...) it started up again as it was programmed to do?
And so the cycle persists...
How long, as a ball park figure, does the boiler need to be operational for in order for a test to be done? A minute, an hour?

 

[ShaunCorbs]

10 minutes ideally but 1-2 minutes

The flame was probably being starved of oxygen and would go out

 

[chrisnchris]

Ah, yes CO....dur...sorry. It will now be ingrained, thanks )