ᐅ Washing machine smells like sewage

Hello,

we have recently encountered the following problem:

when doing laundry, the entire utility room smells like sewage or a chemical, chlorine-like odor. This only happens once the washing machine starts rinsing, meaning when the water is being pumped out.

Some curious and completely puzzling points for me are:

- a new washing machine was purchased, but the problem persists
- it only occurs with a specific wash cycle, which is used most often
- a new built-in trap was installed, but the problem remains the same
- a camera inspection of the drain pipe showed no issues

We have lived here for almost 15 years. The system was newly installed back then and worked fine until last year.
Our plumber has already been here but has no solution.

Is it possible that the machine is drawing water from the sewer during pumping? Even though there is a trap?

I would appreciate any ideas...

Best regards,
Stefan H.

Two questions:

- How often do you wash at 90°C (194°F)?
- Have you ever run a machine cleaning cycle? There are special cleaners for that...

Normally, there is an exposed or concealed trap behind the washing machine connection (wastewater) to prevent odors. There is water standing in it. Maybe when pumping out or shortly afterwards, the pump creates some kind of suction that pulls the water back into the drain hose, causing the odor because the "water seal" in the trap is no longer present. Maybe it helps to simply adjust the position of the drain hose.

90 degrees is not used that often. The new washing machine even has a drum cleaning program, which we have already run a few times, sometimes with dishwasher tablets or detergent.

The exposed siphon has already been replaced. The real question is why the draining process isn’t the same for all wash temperatures? The drainage process should always be consistent, right?

Are there any other openings on the wastewater pipe in the room (e.g., air admittance valve or drain in the middle of the room, rarely used sink/shower) that could be emptied or opened by pressure?

I once had a similar problem in our utility room under certain weather conditions combined with the use of the wastewater pipe.

Washbasin and decommissioned in-wall installation of a toilet, but they are connected to a different drainage pipe.

On the same pipe, our bathroom is connected, and below that, the kitchen with a sink and dishwasher. There is no odor at all...