You are just six months into the first two years of your warranty when Taylor Wimpey are responsible for any defects.
You have reported this IN WRITING to Taylor Wimpey which protects you for this defect until it is properly resolved and fixed. (Not just for the 2 years)
Without a photo and knowing the extent of the problem, I cannot comment how serious this is and whether or not it is likely to fall below the £1,500 NHBC minimum claim value.
If there is a problem with the mortar mix being too weak (not enough cement) - and I know of several cases of this (one of which was a Taylor Wimpey home last year) - then the problem is serious and will only get worse.
At the very least, Taylor Wimpey should inspect the gable-end and other mortar joints.
You too can use a key to see if the mortar is easy scrapped out or crumbles. If it does this is bad!
One thing bearing in mind when you moved in, it is unlikely to be is frost damage as your home will have been started in the spring.
Be aware that as with previous instances I have come across, the house builder, the NHBC and mortar manufacturer will all wriggle and join forces to avoid the expensive solution of rebuilding the brickwork because it will most likely mean the whole development would be similarly affected.
Worse, you internal walls may also have been built with weak mortar.
By the way this would come under "maintenance" and would be excluded under your home insurance.
