Webasto Thermo 90s/st (Setting the Co2 content)

[Staarek]

Hi everyone,

 

I was wondering if anyone could point me in the right direction. I'm carrying out some repairs to my Webasto Thermo 90st (new burner tube, new burner + glow pin and flame failure sensor). Reading the workshop manual I found the following:

 

SETTING THE CO2 CONTENT

It is permitted for the factory-set combustion air quantity to be modified. This is achieved by turning the air regulating screw. Setting procedure Turning clockwise: CO2 value is reduced (let the heater run for about 5 minutes before measuring). Rough setting: Screw the adjusting screw fully in clockwise and then one turn back.

 

Now, i'm having difficulties finding (in the workshop manual) where the "air regulating screw" is, but considering that I'm removing the burner, it might be on of the screws that I had to undo, so I just want to make sure that I can adjust it properly when putting the heater back together. I don't have means of connecting the diagnostic software to the unit, so the "rough setting" will have to do. Thanks in advance for your help!

 

 

Edited February 3, 2020 by Staarek
spelling

[WotEver]

Without the means to correctly measure the CO2 level why would you want to alter the factory setting?

[Staarek]

I don't want to alter the factory setting, but since I took half of the unit apart, I'm thinking that I might have undone the air regulating screw when dismantling it (to access the burner etc) as the manual doesn't specify which screw that is.

[WotEver]

Unfortunately any Gas Safe Bod who knows is unlikely to tell you - they’re very protective of their profession. Perhaps someone else who has one (or has access to a manual) might know. 

[Ex Brummie]

I don't know exactly where the air screw is, but if you have disturbed it, either the burner will start with a splutter if too weak, or will smoke (black) if too rich, white smoke indicates unburnt fuel.  If you need to adjust, remember to do it a little at a time, and wait a minute or so to see the full effect. If you start as advised, then be patient.

Measuring the CO2 content requires a flue gas analyser. 

[Staarek]

Just now, Ex Brummie said:

I don't know exactly where the air screw is, but if you have disturbed it, either the burner will start with a splutter if too weak, or will smoke (black) if too rich, white smoke indicates unburnt fuel.  If you need to adjust, remember to do it a little at a time, and wait a minute or so to see the full effect. If you start as advised, then be patient.

Measuring the CO2 content requires a flue gas analyser. 

Thanks very much!

[WotEver]

3 hours ago, Staarek said:

Thanks very much!

See here;

 

[MtB]

18 hours ago, WotEver said:

Unfortunately any Gas Safe Bod who knows is unlikely to tell you - they’re very protective of their profession. Perhaps someone else who has one (or has access to a manual) might know. 

 

Is this a gas heater then? I would happily tell the OP if I knew!

 

I agree the attitude used to exist amongst some of the more dinosaur gas bods but it has been mostly stamped out nowadays. Manuals are all in the public domain and there are no restrictions on who may have them. Never have been.

 

Curious that tvayle talks about setting the CO, while the OP is asking about setting the CO2.  The two are related on a gas appliance but not necessarily directly. Not so sure about diesel appliances. 

 

 

 

 

[Tony Brooks]

33 minutes ago, Mike the Boilerman said:

 

Is this a gas heater then? I would happily tell the OP if I knew!

 

I agree the attitude used to exist amongst some of the more dinosaur gas bods but it has been mostly stamped out nowadays. Manuals are all in the public domain and there are no restrictions on who may have them. Never have been.

 

Curious that tvayle talks about setting the CO, while the OP is asking about setting the CO2.  The two are related on a gas appliance but not necessarily directly. Not so sure about diesel appliances. 

 

 

 

 

 

A bit off topic but likewise on some vehicle exhaust gas analysers you also get an O2 reading as well as CO and CO2. As Mike says related but not necessarily directly. For petrol vehicles a high O2 and low CO may well pass an emission test but will be running weak so could suffer detonation and engine damage (not so much now the brains run at the detonation point and retard the ignition to suit).

[tvayle@gmail.com]

Hi 

I just seen Mike's comment co 2 was what I meant. I wouldn't have thought you would have touched the screw as it set at an angle on the combustion air blower and as the heater parts with   a clamp arrangement and it's a screw by it's self but as Mike said if you need to alter it just move it slightly each time 

[WotEver]

3 hours ago, Mike the Boilerman said:

Is this a gas heater then? I would happily tell the OP if I knew!

D’oh!  Me stoopid. 
 

I’m so used to seeing posts warning of dire consequences if you so much as look at a screw on a gas boiler cover on plumbersforums.net if you’re not GSR that I got all carried away as soon as I saw ‘CO2 adjustment’ mentioned. 
 

3 hours ago, Mike the Boilerman said:

I agree the attitude used to exist amongst some of the more dinosaur gas bods but it has been mostly stamped out nowadays.

Not on the above mentioned forum - it’s fully alive and kicking. 

[MtB]

10 minutes ago, WotEver said:

D’oh!  Me stoopid. 
 

I’m so used to seeing posts warning of dire consequences if you so much as look at a screw on a gas boiler cover on plumbersforums.net if you’re not GSR that I got all carried away as soon as I saw ‘CO2 adjustment’ mentioned. 
 

Not on the above mentioned forum - it’s fully alive and kicking. 

just had a quick look. Its hard to find any content on there to read in amongst the avalanche of adverts!! 
 

[WotEver]

6 minutes ago, Mike the Boilerman said:

just had a quick look. Its hard to find any content on there to read in amongst the avalanche of adverts!! 

Yes, it’s pretty horrid, isn’t it?

 

Here’s an example of what I meant...

https://www.plumbersforums.net/threads/worcester-bosch-37cdi-combi-leaking.112585/#post-1081619

[Ex Brummie]

8 hours ago, Tony Brooks said:

 

A bit off topic but likewise on some vehicle exhaust gas analysers you also get an O2 reading as well as CO and CO2. As Mike says related but not necessarily directly. For petrol vehicles a high O2 and low CO may well pass an emission test but will be running weak so could suffer detonation and engine damage (not so much now the brains run at the detonation point and retard the ignition to suit).

On oil burning appliances, a flue gas analyser will measure oxygen, carbon monoxide and carbon dioxide. The aim is to achieve as high a CO2 content without smoke. The O2 reading indicates the 'excess air' in combustion and the relationship between the two, when calculated along with the flue temperature gives a gross or nett efficiency, depending whether a gross or nett temperature is used. (Nett is the actual flue temperature minus the ambient temperature.)

Without access to a flue gas analyser, if you set the rough air setting as described in the instructions, an experienced ear can assess the smoothness of startup, and the exhaust can be checked for smoke.  CO should normally be below 50 ppm and is an indication of flame instability or impingement if CO2 an temperature measurement is within limits.

Edited February 4, 2020 by Ex Brummie
Add the last bit.