Sewer smell in home

cool_dude_2000

Since working on the soil pipe to plumb in new toilet, shower and basin waste in the loft, I am experiencing problems with sewer smell coming into the house below.

The soil pipe runs vertically up through the house and is boxed in on ground and first floor to protrude through the roof where it is externally vented.

I have converted a storage room in our converted loft into an ensuite wetroom with a shower, wash basin and wall hung toilet. To accommodate their waste outlets, I have cut into the soil pipe at loft level and inserted a push fit slip coupling and branch connector which the toilet and basin connect into. The shower waste pipe connects to the soil pipe via solvent strapped boss connection. There are no water leaks when I flush the toilet and run the taps.

However, in the corresponding room below, there are sewer smells emitted from the boxed off soil pipe which runs into the loft. Adjacent to this room is the bathroom. An examination of the soil pipe here confirms there are no leaks from the bathroom connection.

The loft room basin and toilet both have traps filled with water. The waste outlet for the shower is blocked up with a rag.

I am struggling to understand why the sewer smell continues to emanate? Particularly as there is no smell in the loft wet room, but in the room below? Do I need to add in an air admittance valve to the new waste outlets in the loft?

I have added a diagram below.

I welcome any thoughts?

Alter_ego

Could flushing toilet in loft room be creating suction/vacuum which is siphoning one of the traps in the bathroom below?

cool_dude_2000

Thats what i thought was possible.

But I can still see water in the 1st floor shower trap. Plus there are no smells coming from the bathroom unit plug holes.

Would fitting an air admittance valve in the loft solve this do you think? I would have thought the external vent would take care of this.