Foul Waste system venting through shower?

[WithIcePlease]

Foul egg smell is coming through the shower drain. All the traps are clean, water all free flowing through out pipes. I'm wondering if this could be to venting through the p- trap in the shower?? I have a durgo valve in the loft

is this an original bathroom, from when the house was built? Or an extra one added later?

A later one may have poorly designed drainage pipes. The Durgo is not a good sign.

Our shower trap doesn’t really isolate the drain air like a traditional u-bend would. The trap catches any solid thing such as if you drop your ring but the water drains through a higher level hole into the waste pipe (think of a pipe connected toward the top of a bucket). Proper venting of the waste pipes shouldn’t create a problem though.
As a matter of interest, what’s so bad about Durga valves @PigletJohn?

A durgo is supposed to suck air in when pressure in the drain is low, but not allow it to escape when pressure is high

(but when the valves sticks, they will do both, or neither)

More traditionally, a soil pipe is open at the top, which is above the level of your windows, and effortlessly ventilates in and out.

Durgos are most often fitted when a new or additional bathroom is installed and the builders can't be arsed to have a roofer put a special tile for it to go through. They are often walled up inside the bathroom so you have to smash tiles and break open the wall to change the valve when they stick.

p.s.

it's possible that the shower waste pipe might have too shallow a slope on it, allowing congealed conditioner and soap to collect. Washing soda crystals may help here

The shower trap should have a dip tube to prevent water being sucked out when there is suction in the drain, for example after flushing a WC or emptying a full bath. In that case, the smell would stop if your pour a cup of water over it, or flop a wet flannel over the mushroom to seal it.

Mcalpine make some very good traps.

Modern shower traps are designed so they can be cleaned and serviced from above, rather than below like basin and bath traps, so you have more chance of cleaning the hair out.

from your description, I wonder if the dip tube or bucket might be missing from yours.

I can't find a very good pic

but this might help

www.contour-showers.co.uk/products/shower-wastes/shower-tray-gravity-wastes#ae-image-3

I’d swap the Durgo in the loft , see if that’s faulty.

All the houses on this development have durgos. I have actually had a near identical house a few hundred yards away and no problem there.
Yes it is an added en-suite with the shower. The drop on the waste pipe from shower is sufficient. It's at about 11 degrees.
I have had a springy wire down the waste and it was completely clean when it came back. The p trap is clean. I have put about 6 lots of drain cleaner down as well as bicarb and vinegar. I've also plunged it (both bath and shower) covering plugs and overflows and nothing at all came back.
As showers have outlet open to air because of p traps rather then u bends I wondered if the durgo may be the problem

Thank you all
The shower trap I have is the same type as in the diagram I think Piglet john. Like this pic here. Completely white inside.
The smell comes and goes and seems to be independent of if bath bath drained recently or any shower drainage

Does the trap have both the tube and the cap, and does the mushroom screw down to seal?

Flop a wet flannel over it and see if that blocks the smell.

Didn't attach pic last time sorry. It's like this one
I have put a rubber plug in it and that seems to have stopped the smell coming out

Have you checked your inspection chambers for blockages in the main waste pipes?

It's on a development that shares inspection chambers and water services provided under the leasehold. No one else has experienced problems in nearby houses. I don't think this house was well maintained before purchase as found a leak within days of moving in, heaters didn't work, tank needed replacing due to lime scale and water wouldn't heat up
I've got a builder upstairs now so I'll see what he says

Well all explained now! The cowboys who did the en-suite got rid of the durgo valve completely and capped it off. So the system was trying to vent through my shower!
Another job for my builder....
Thank you all

Ask about having it vented through the roof.

A Durgo will not vent odours and sewer gases into the loft (unless it is jammed, which is most undesirable).

I think I will piglet John it's best all round while I'm having the work done