Understanding Ignition transformers

Hi, I hope someone can help me understand the difference between to following transformer information.

I have an old Oil Fired Rayburn and the ignition transformer has failed. I have sourced a new transformer, however, the one that has been sent to me by Rayburn has a different transformer code than the one I have taken off. 
I have assumed the one sent by Rayburn is the correct one, but with me not being an electrician I don't just understand the difference to the one that was on and the one I have been given. The reason I am asking is that there is over £100 difference in price.

Below I have listed the different specs of the transformers that were on and want I have been sent. All models are from the same make  - Cofi 
1. Is the transformer which has gone faulty
2. Is the transformer that has been sent by Rayburn as a replacement
3. Is an alternative model I could purchase at a lot less money

I would like to now want the 25% su 4' means and would the others work ok?

1.  TRE820    230V    50Hz    2×4 kV    20 mA    19% su 3’    Earthed center
2. TRS1020    230V    50Hz    2×5 kV    20 mA    25% su 4′    Earthed center
3. TRS1020    230V    50Hz    2×5 kV    20 mA    33% su 4′    Earthed center

Parmeko were the main suppliers of ignition transformers until the last 10 years or so. The replacement is probably the best you will get.

Get an electrician to fit it for you, 8,000V up your arm bloody hurts.

The percentage is duty cycle, (it's Italian, & su = on), which makes the 33% more capable than any lower percentage. I've no idea what the 4' refers to. 

This lot appear to have the one you originally wanted for £50ish.

http://www.mkwheatingcontrols.co.uk/-c-250_251_434_107.html?oscid=diarsntnc34f8lcfpihk5mmqk0

Geoff1946 said:

 

Click to expand...

 Thanks for the reply.

If I am using the one at 25%  would it cause any damage if I used the one at 33 %?

I believe that the 4' means 4 minutes 

You are probably right about the 4 minutes. Then, assuming both our deductions are correct 

the 25% one could be operated for 4 minutes then need 12 minutes to cool down. The 33% one could operate for 4 minutes then need 8 minutes cooling. So no harm would result in normal use.

As Tony says though, do be careful. Touching the wrong thing when it tries to light could spoil your whole day!

I would still be inclined to get the correct part if possible as there will be other differences which we are assuming don't matter.