riello rdb burner (pump problems)?

Hi There i've got a fustrating problem with my reillo pump, the burner is rellio rbd with red cover on front ,
since it's done 3 pumps in , in 6months i need to find where the problem lyes and ive done everything to make sure fuel is getting to pump freely , cleaned the fliter at the tank , checked fuel line for cinks checked for air locks even had a service etc ..
once i get it going , with a new pump it runs fine for about a month then starts getting a bit noisey after a few weeks the pump will cease then i need a new one at 55 quid , ive only just had a service and was wondering if the nozzle was worn could this cause the pump to over work to a pace where it cant handle anymore , or do i need to get pressure checked after fitting the pump or would the burner be running the pump to quick .
Has anyone had the same problem as me and I would be gratefull if anyone could advise me about it

Thankyou - Dave ...