Gas Valve adjustment

[Robert Tyrrell]

I know that I should remember all this stuff but at the moment I kinda need a refresher if there's anyone willing to remind me?
I would like to be reminded of how the gas valve adjustments affect the CO & CO2 readings as I think that I might have a dodgy sensor on my fga, despite the fact that it's just come back from a calibration with Kane.

I tried getting the correct CO2 values by adjusting the "A" throttle and the "B" offset adjustments but I still get a very high CO reading even when the CO2 is correct, and Vaillant's manual just gives the CO2 values with no explanation of how to control the CO. The gas rate is within the correct parameters btw.
The boiler is a room sealed fan assisted balanced flue etc etc so it's all going outside and I have warned them that they need to have a CO alarm in the room along with the fact that I will be back to make 'adjustments'.

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[bewsh]

The CO should come down when adjusting the CO2.

If it's still high readings of CO then there's a problem somewhere. If it's a Vaillant, then the flue seals usually fail because they've been pushed out of damaged with assembling the flue. So check the air intake with the combustion cover fitted.

Or it may need a strip down to check condition of burner/heat exchanger - new burner gasket required then as well.

Also, if it's the older ones with the condensate collector at the rear of the heat exchanger, these tend to crack with age, so get a mirror around the back to check that.

 

[Robert Tyrrell]

Thanks for that. I'll look at all that when I go back but what I really want to know is the relationship between the two parts of the gas valve. I haven't had that much instruction on them and as I've only serviced three boilers, none of which needed adjusting, I haven't had much practice since qualifying.

 

[Neil K]

Good question Robert, I'll watch this thread with interest

 

[lame plumber]

have a play with your boiler at home, it is all down to maths really, the sensor detects co2 fm memory and works the rest out. there is a lot out there if you google it, some manuals also explain how it works as well

 

[glenntaf]

All you are basically doing is altering the gas to air ratio that enters the combustion chamber to be burnt, A is to alter the ratio for test mode max and B is how to alter test mode minimum. When you say you are getting a high CO reading, what do you call high?? Many boilers allow up to around 200 - 250 ppm in test mode max. There are other factors that can effect CO, but if the boiler is a few years old it may need a good strip down using the manufacturers seals and service kit. Paying particular attention to cleaning out the combustion chamber. P.s also check the condensate trap isn't full of debris!!!!

 

[Robert Tyrrell]

Thanks for that glentaf, the reading was around the 200 mark, but as you say, it was in test mode - oh, and thanks for the explanation of what does what on the gas valve. I did know that bit but it's always good to have someone remind you

 

[Billy Bob Bob]

200 ppm,thats quite high,what was your low reading?

 

[buckley plumb]

Same gas valve as on glowworm hxi prone for problems .

 

[Robert Tyrrell]

200 ppm,thats quite high,what was your low reading?

I don't actually remember but it was still quite high, not in the hundreds though.

 

[buckley plumb]

Have you forced boiler into low and high using and tested and tried to set. Had a few go faulty but boiler screams in low rate

 

[Paul - PDS]

Check FGA tube and seals aswell. If it's not sealed can give high CO readings too

 

[Simon F]

200 ppm is high, usually about 50-100.
as said (post 6) make sure you are in the test mode and use the correct screw for that mode.
only small turns and wait till the analyser cathces up.
the cover off srew B can affect the reading so cheack aswell when it is back on.

after making any adjustmesnts check both high and low settings again.
the difficulty with the high setting can be the boiler getting to hot and shutting down.