Hairline crack in extension wall going though brickwork

[GGGG]

hello, I hope you can help advise on what to do about hairline crack we have found.

In our ground floor extension where we have our kitchen we noticed a crack (1-2 mm diameter) going through the plasterwork. We found this when removing the wall units and can see it goes up to the coving (picture attached), but I am not sure how far down as this is hidden by the base units. We cut out a little of the plaster to see if the crack goes through the wall and we can feel air flow from the outside so assume it does go to the outside. The wall is plastered, then breeze block and then brickwork. The neighbour has an extension too and so I guess when our extension was built they could not render the side wall (picture attached). It also means we can't see what is happening on the outside of the wall.

Any advice and thoughts greatly appreciated.

 

[^woody^]

It's a thermal [shrinkage] crack on the blockwork only. Search on those terms for the repair work. It's not a structural crack

 

[GGGG]

Thanks Woody, that is a relief. I have had Search on the web and there seems to be two options: 1, hollow out and fill with flexible filler or 2, also remove the plaster around the crack use eml and replaster. I am thinking as this is not a structural problem and the wall is pretty much hidden by units option 1 is probably the best as it is the easiest. Any recommendations on the filler I should be using? Thank you for your help.