Baxi 105e

[dan2071]

Hi, i was just wondering if anyone would be able to educate me on this one.

I was servicing a 105e today and i ran the hw tap so that it fired on full rate and rectified, i then disconnected the ignition lead off the spark gen, thinking this would cut the flame and result in lock out. But it kept running.

I know or rather i thought i knew how flame rectification works -

PCB sends VAC to Spark Gen > Spark Gen Sparks > Ignites Gas > Spark Gen then sends a AC current through the flame > rectified into VDC > down the rectification probe / lead and back to the board.

So why when i disconnected the ignition lead did the boiler not cut the gas?

I hope this makes sense.

Thanks, Dan

PS. does anyone know how long it takes to be accepted into the combustion chamber forum? I've been waiting two days

 

[Dan Robinson]

Depends on the Admin - alert them to this thread - it might speed things up.

 

[picasso]

The 105e has two electrodes, one is the spark electrode and the other is the flame sensor.

 

[Agile]

That should have been obvious to the OP !

I think he needs a bit more study/training!

Also to be gas reg and ask in the CC !

 

[picasso]

We all gotta start somewhere.

 

[Agile]

Thats true, but he joined the forum over FIVE years ago!

If he is servicing boilers he needs to know these basics. I would expect any trainee of mine to never make that mistake after the first three weeks with me.

Otherwise I would be wasting my time!

 

[dan2071]

There are two electrodes on the 105. One is the spark electrode and one is the rectification probe (flame sensing electrode). If the VAC isnt coming from the spark electrode and rectifying across the flame and back down the flame sensing electrode then where is the VAC coming from???

 

[dan2071]

By cutting the VAC going to the ignition electrode, this should have in turn stopped the rectification process?

 

[gaswizzard]

If the VAC isnt coming from the spark electrode and rectifying across the flame and back down the flame sensing electrode then where is the VAC coming from???

This is not how rectification works , AC voltage is sent to rec probe which in turn converts to DC via flame ionisation and back to control board via burner/ground.

AC is rectified to DC due to surface area of probe/burner.

 

[gaswizzard]

By cutting the VAC going to the ignition electrode, this should have in turn stopped the rectification process?

No it wouldn't.

 

[dan2071]

Thankyou