Dirty Groat

Help....Im asking for any advise on how to bring back the whiteness to some of the white grouting on my bathroom tiles.
I bought some HG grout cleaner which has done a remarkable good job on cleaning the grouting in the kithcen around the back of the cooker and around the sink. Very pleased with the result.
Move on the bathroom and no way will it bring back the grouting to white!
So I gets to thinking whats going on here?
Kichen would be a greasy stain which the cleaner removed okay.
Bathroom is more likely to be an organic colouring which should be brightened up with bleach. Ok, out with the bleach and let it soak awhile, the result is no change, I still have the greyish colouring. Another strange thing is its only a few areas in the bathroom that seem to be affected.
Could it be different grout? I did the kitchen, a tile tech did the bathroom.
Im stumped at this time. I know the ultimate answer is to hack all the grout agian and redo it.....
This picture is contrast enhanced to show the staining more.
Anybody any suggestion on how I can brighten this lot up

Please....

 

Hi Capney,

I had to re read the title as I wasn't sure at first what you were talking about:flag::D I have found this item on the net,but not sure whether it is any good or not.I usually use a toothbrush and some thick bleach making sure I have good ventilation{open window} when i do my tiles and it works up to a point but probably in your case you might be better to use the product in the link.I believe also that you can by Grout pens but don't know whether they are any good either.

Anyway he is the link....
http://www.wickes.co.uk/invt/166158

 

I thought you meant a dirty goat!

The bleach and toothbrush works well - lots of elbow grease required.