On Thursday, August 4, 2016 at 7:26:26 PM UTC+1, Fredxxx wrote:
On 04/08/2016 15:09, John wrote:

snip

Burners may rot or get blocked jets but don't generally "fail" so if it's
not lighting you need to look "upstream".

It will light, but blue flames immediately appear around the front of the boiler casing.

That doesn't sound right at all. Can you provide a photo?

I have known old burners needing a very good clean where the holes
become partially blocked. Again remove and lets see some photos.

Thanks - I think I'll have to get the plumber back and have a close look at this. Thanks for your suggestion.

John