Spark Generator/Ignitor - How strong a spark is required?

[Siftah]

Hi All,
I've an ancient Worcester Heatslave 9.24 (Balanced flue, electronic, white fronted - 47-311-02) Combi boiler.

It's clearly an ancient boiler and quite ready for replacing, however it's been reasonable reliable for me and I've only had to change basic parts until now - Pump and Diaphragm.

It seemed to have gone out some time on Friday evening and didn't re-light, electronically it seems fine and the pump is still running from what I can hear.

I don't seem to be able to re-light the pilot light though - I'm unable to see a spark in when I look through the window on the boiler and depress the red spark ignitor button.

I suspected therefore the spark igniter needs replacing and have located the part online and ordered one.

However, I've removed the old one and testing it on the bench it does seem to be generating a spark, the white cable from it was good and appears to be free of cracks or bends/breaks. It dissappears up into the metal shield, I've been unable to verify it from that point onwards as I've never removed that portion of the boiler (just the white removable cover on the front).

My question is: Does the spark on this thing look strong enough that it should work? Am I perhaps looking for an earth somewhere, rather than needing a new ignitor?

There's a video of the spark ignitor being fired "on the bench", here:

And for reference here is the boiler:

All help or guidance will be most gratefully received!
Thanks,
John

 

[bengasman]

You have gone over and beyond what is normally accepted as safe diy; you should get a RGI in to repair and make safe.

 

[Agile]

You need about 13,000 volts to create the spark when the gap is 3-4 mm wide.

Have you measured the voltage you are getting?

Tony

 

[Siftah]

You have gone over and beyond what is normally accepted as safe diy; you should get a RGI in to repair and make safe.

Safety comments accepted and duly noted - I've really not done anything as dangerous as re-wiring a plug in this instance though.

The spark igniter is a simple 2 screw and one spade terminal to remove, I've not had to remove anything other than the front cover (designed for consumer removal).

 

[Siftah]

You need about 13,000 volts to create the spark when the gap is 3-4 mm wide.

Have you measured the voltage you are getting?

Tony

Thanks for the response Tony - I'm not sure whether you're suggesting to measure the voltage or whether you're just mentioning what is required?

I can create a spark with it about 1cm long, using the screwdriver about 2mm from the terminal it'll arc between that and the base plate of the ignitor (about 1cm spark jump in total) - You can see this in the YouTube video I posted.

That suggested to me it's probably working "well enough" and that it's likely to be earthing somewhere inside the boiler and hence not lighting the pilot?

If that's the case and I don't just need a new ignitor/spark generator, then I'll have to call in a RGI.

 

[expertgasman]

There is nothing wromg with that piezo. The fault may well be on the electrode, but the removal, inspection and replacement is RGI work

 

[Siftah]

There is nothing wromg with that piezo. The fault may well be on the electrode, but the removal, inspection and replacement is RGI work

Thanks for this!

 

[Agile]

The spark may well be able to jump nearly 10mm in air.

However at that length the spark will be weak and spread over the 10 mm.

At the correct setting the spark draws more current and is concentrated the the 3-4 mm and thus reaches a higher temperature and will reliably ignite a gas/air mixture in the correct ration.

With dry air and balls at each end 33 kV is needed to jump 10 mm. That reduces if the electrodes are sharp and if moisture is present.

So if the gap was 3.3 mm then the worst case breakdown voltage required would be 11 kV.

Those peizo ignitors probably produce closer to 20 kV. Thus a spark will potentially jump across many different paths if the ignition gap is oversized or a lead is disconnected.

You should not be suggesting that Dick on this forum as it is an encouragement to readers to try things they are not competent for.

Tony

 

[RichieHoneybucket]

.................or blocked pilot injector??!!!

But of course as stated above, you must call in a RGI to investigate further.

 

[Siftah]

.................or blocked pilot injector??!!!

Possibly, though I'm not currently seeing a spark when looking through the pilot light checking window, so I would guess the lack of spark must be an issue too :\

 

[RichieHoneybucket]

The spark may well be able to jump nearly 10mm in air.

However at that length the spark will be weak and spread over the 10 mm.

At the correct setting the spark draws more current and is concentrated the the 3-4 mm and thus reaches a higher temperature and will reliably ignite a gas/air mixture in the correct ration.

With dry air and balls at each end 33 kV is needed to jump 10 mm. That reduces if the electrodes are sharp and if moisture is present.

So if the gap was 3.3 mm then the worst case breakdown voltage required would be 11 kV.

Those peizo ignitors probably produce closer to 20 kV. Thus a spark will potentially jump across many different paths if the ignition gap is oversized or a lead is disconnected.

You should not be suggesting that Dick on this forum as it is an encouragement to readers to try things they are not competent for.

Tony

Sorry, you're quite right Tony.