Slow running fan effect combustion?

[dan_the_plumber]

Hi all.
Before I begin, im talking about older ‘on/off’ fans on atmospheric burners. I am not talking about the newer variable speed fans with zero rated governors on condensing boilers.
All I’m wondering is, can an on/off fan run slowly when supplied with 240vac? Would this cause higher readings of CO as the POC is not clearing the boiler fast enough?
Thank you

 

[Harvest Fields]

Surely if it is an on/off fan. It should be spinning at a constant speed whilst it has 240v. If it is slowly spinning and there is a constatnt 240v supply. A new fan would be needed. On the older boilers if the fan was struggling, the flame would cut out or the boiler would keep cycling on/off.

 

[dan_the_plumber]

Yeah I’m just wondering what the most common cause of poor combustion results would be on atmospheric burners?
Inlet pressure is fine
Gas rate is fine
Burner pressure is fine
But still getting 0.0039
So I’m wondering, slow running fan?, dirty heat exchanger? dirty hood? blocked flue? Any more?

 

[Harvest Fields]

I would look at the heat ex or flue

 

[townfanjon]

Can you spin the fan blades with your finger , do they spin and stop or continue spinning ?
Whats the boiler?

 

[dan_the_plumber]

Yeah this particular fan seems to spin freely. It’s a Worcester 28i RSF. I’m only asking coz I’ve got a load of them to do and need to save time if it comes up again

 

[dan_the_plumber]

Actually I’m not sure if these fans have plastic Venturi inside, I know they have on some Ferrolis and they can go brittle and fall apart. I’ll look into it

 

[dan_the_plumber]

Actually I just looked up the exeptable combustion ratio for this boiler:
0.003-0.007 ! Older model, how things have changed

 

[king of pipes]

Case seals intact ? Kop

 

[dan_the_plumber]

Case seals intact ? Kop

Yes, I did check them. Really nice rubber seals on that model actually