flue gas analysis / performance testing

[ACOperson]

One for the Corgi service engineers out there:

Where is the best / correct test point for combustion analysis (CO/CO2 ratio) on open flued & back boilers. Have never had to do this before myself and the Corgi publication that deals with Fga's doesn't cover this. Used my FgA on only room sealed boilers and to do in room CO checks.

I'm pretty sure that to take an analysis on a standard open flued appliance I would do this from the draught diverter, but what about on back boilers?

Not sure where to take either with or without fire in place.

Any help would be appreciated.

Cheers

 

[ollski]

Just stick the probe up the flue, fire doesn't need an fga check just spillage. Usually read .0003 as a max. after a clean out.

 

[corgiman]

I usually (like oll) stick it up the draught diverter, but as all old boilers never mention it (why would they?) why do we do it

I always do but have no idea why

 

[baxpoti]

For an inset type BBU
With fire in place (switched off)
Run BBU for a minimum of 30 minutes
Place probe adjacent to the dilution tube
A CO/CO² ratio reading of 0.008 or below is acceptable
CO below 10ppm


For older BBUs
Remove fire front
Run BBU for a minimum of 30 minutes
Place probe, centre of flue in at least 200mm
A CO/CO² ratio reading of 0.008 or below is acceptable
CO below 10ppm

 

[corgiman]

For an inset type BBU
With fire in place (switched off)
Run BBU for a minimum of 30 minutes
Place probe adjacent to the dilution tube
A CO/CO² ratio reading of 0.008 or below is acceptable
CO below 10ppm


For older BBUs
Remove fire front
Run BBU for a minimum of 30 minutes
Place probe, centre of flue in at least 200mm
A CO/CO² ratio reading of 0.008 or below is acceptable
CO below 10ppm

Sorry Bax but if the original MI dont ask for it why do it?

Old fashion kinda gent me, do what the MI's say end of!!

not being a plum just interested?

 

[ACOperson]

Going to do some work over the summer for a social housing contractor who want all their guys to do FG analyses for all boilers they come across, including open flued, BBU's, etc.

Theres a CORGI publication which has a table stating maximum permissable CO/CO2 ratios, and so they will ask us to use these figures in place of MI's etc.

On a BBU, eg Baxi Bermuda, I'm assuming that the correct place to take these readings is in between the 2 baffles under the flue spigot and above the heat exchanger?? Not sure if thats what Baxpoti means by the 'dulution tube' is it? Cheers

 

[Agile]

I dont see how an FGA testing point can be meaningful if its in effect after a draught diverted as thats a flue dilution system.

On a typical 552 I would do it under the horizontal baffle AND block the fire connection point. ( Dont normally do it at all though )

That would give me the real undiluted POC from the boiler!

To an experienced engineer used to assessing flame picture there seems little to be gained on an old boiler by an FGA but for a newbee it might aid consistency.

I would always suggest building up a portfolio of readings on the same model at the same test point so that a problem unit can easily be detected.

Tony

 

[ACOperson]

Same should go for any other open flued boiler then? If this is the case then taking it AFTER the draught diverter is wrong? Can't see where else I can take it though, eg on floorstanding boiler.

I thought I read something in this new-ish CORGI publication about CO/CO2 ratio being the same even if after dilution?...

Edit: Sorry I should have mentioned that all they want us to do is CO/CO2 ratio's, not full flue gas analysis. Cheers

 

[Agile]

Thats the problem, there is no hole fitted as a test point !

The CO/CO² ratio will theoretically be the same even if diluted

However, these FGA measurements are pretty coarse and inaccurate at the best of times.

The ratio of POC to added air from a draught diverter is both unknown and very variable.

To give a more consistant comparisom between boilers of the same model I would always measure it BEFORE the draught diverter.

Many of the floor standing boilers have a sloping inspection cover towards the front and I would do it from there with the aperture blocked as mush as possible.

If you are going to do a lot of the same kind then why not make an adapter plate with an FGA test hole and you can then be totally consistent between each boiler?

Tony

 

[Paul Barker]

Thats the problem, there is no hole fitted as a test point !
Tony

In our town a gas fiutter had drilled a hole to test flue gases and taped it over with that metal tape. Customer asked BG to take it on service contract they said he had to have new secondary flue starter pipe because of it before they would take it on. I was given the job, must have been cheaper than BG. I don't know why they didn't get the phantom hole driller back.

Careful not to do stuff to older appliances in the interest of modern equipment.

I say, service, correct ventilation, good flame picture pass flow and spillage tests, analyser stays in the van.

 

[Agile]

That hole would have been after the draught diverter and not in my prefered location.

Of course you should not modify the appliance but make up a replacement inspection plate with a hole or whatever just for use with an FGA.

I am beging to warm tot he idea of FGA measurements for social housing servicing as it proves the gas man really went there and at least did something!

Tony

 

[ACOperson]

Cheers guys,

I don't think that I'm going to have time to make up inspection plates etc for this job, they just want us to go in, take the reading and be out in 30-45 minutes.

I'm definitely not drilling anything either!

Think I will just experiment with the back boilers, see which point gives the expected readings. I'm going to be stripping all the OF ones I come across anyway, but they want us to show a printout of CO/CO2 for each one also. I just want to make sure I'm doing it right, rather than having some social housing manager telling me I'm not doing things right because I've put the damn FGA probe in the wrong place or something.

Would still be interested to hear from Baxpoti about this dilution tube...

Thanks

 

[namsag]

Surely any reading from a back boiler should be taken with the fire in situ as this is part of the appliance and affects the amount of air getting to the boiler burner flue pull etc

 

[baxpoti]

Surely any reading from a back boiler should be taken with the fire in situ as this is part of the appliance and affects the amount of air getting to the boiler burner flue pull etc

Fires can remain in place although older fires need the case off to access the flue.
A back boiler in combination with fire, the CO/CO² 'action level' is 0.02

Insets can remain in place, because you can access the boiler flue very easily, without the need to remove.

The quoted CO ppm is as per the OPs question. 10ppm measured in the room.

There is no requirement to FGA a back boiler, although a reading before and after a service, should prove how important servicing is.

 

[bripl]

10 ppm are you sure about that.just done 8 strata boilers all brand new ppm readings were around the 35/40 mark.i may be wrong but remember some one saying on gas boilers below 100 is ok 200 on oil.with a fga you need to understand ALL THE FIGURES the ratio on its own can be misleading.for accuracy you need to take the readings below the draught diverter