Sewage or stagnant water smell in house

[drucook]

Hi - i wonder if anyone can offer any advice on the following. We have a five year old house and two months ago had the boiler replaced with a Worcester-Bosch 440cdi. Two months on we now have a sewage / stagnant water smell from the bottom of the stairs to the top which varies in strength from day to day. I am not sure if the boiler replacement has anything to do with it, but it very unpleasant. The toilets flush fine and the shower drain runs okay as well so i am not sure where to start with investigating it. Any help would be appreciated

 

[Plumbstar Tom]

check your drains and are they're any man holes on your drive, side way or garden? check them too

 

[GQuigley67]

could be something to do with the condensate maybe the engineer didn't fill up syphon or install a trap, maybe washing machine is interfeering with it...