My sewer is backed up to the first floor toilet, the ground floor toilet is working OK.
When I flush, the sewage goes into the shower.
The stack for the first floor toilet has a polyvalve on it, and when I took this off, it started flushing properly, but once back on, it immediately started flushing back into the shower.
I think this means that the there is sewage in the stack which is not draining when I take the polyvalve off.
We spoke to the housing development customer services and they unblocked the sewage pump and it's now flushing better than it was and it's not going into the shower anymore. Although it's still quite a slow flush.

I'd like to know why the ground floor toilet isn't affected, when the sewage is backed up to the first floor, way above the ground floor toilet.
I'd also like to know how the sewage can back up to the first floor.
This has happened three times in 20 months, is it likely to be a faulty sewage pump or a problem with the pipes.

Thanks.

Where do you live and are you talking about a sewer election pump? Polyvalve is the name of a company, not a part. Please tell us more about you valve and what it does.

Hi,

Unfortunately I don't know much about the sewage pump, it's what the developers call it. Because we live on a shallow hill, I assume it's needed to move the sewage up to the main sewer line. I believe the pump only deals with sewage, since all my other services run OK when the pump fails.
The valve sits at the top of the stack and prevents sewer gas from exiting into the roof space. When the toilet is flushed, this creates a vacuum and opens the valve to allow air in to equalise the pressure in the stack. Then it closes again, stopping sewer gas from exiting.

Hope this helps.

The stack for the first floor toilet has a polyvalve on it, and when I took this off, it started flushing properly, but once back on, it immediately started flushing back into the shower. I think this means that the there is sewage in the stack which is not draining when I take the polyvalve off.
And I thinki that your "polyvalve" is a AAV, (Air admittance Valve),(see image) that's gone sour and is no longer working. Replace the AAV and flush your troubles away. Good luck, Tom

I think Tom has the right picture in his mind. Maybe polyvalve is a manufacturer of AAVs along with sveral others like Studor.

I removed the AAV and expected the sewage backup to lower, but it remained at the same height.
It's possible the AAV is faulty, but you'd expect things to start working more normally once you've removed it.
When I replaced the AAV after removing it, the toilet started flushing back into the shower immediately.