Room thermostat will not regulate?

My boiler has recently been replaced from a (baxi solo 2)to a (baxi solo he 15 condencing boiler) and since this replacement i am unable to control my room thermostat,i have been advised by a baxi engineer that that the thermostat had been previolsy incorrectly wired but was not allowed to advise me how to wire it correctly.any advice would be very much appreiciated. i have a honeywell mechanical themostat wires in situ are as follwes (earth)+(blue in 2)+(yellow in 3)+(red in 1)? might it help to switch any around