Any good garage can test for HGF by a compression check, pressure check and also sniffing the air in the coolant expansion tank with the MOT emissions probe to test for combustion gases in the coolant.
Even though it's nly 2 years since the EGR valve was changed check this 1st as they do seem to clog up quickly, also depends on how the car is driven and where,all diesels need a good long motorway run regularly to keep both the EGR and DPF happy.
Could also be a software issue with the DPF regeneration?