Questions about soil stack

[Splidge]

Hi
We moved into our present house in 1989, when it was about 3 years old. The house has an internal soil stack, into which fed a loo and sink downstairs and a loo, sink and bath upstairs. The stack reached up to a few inches above sink level.
About 10 years ago, we had the upstairs suite replaced by a well-known bathroom company as part of a complete refit. During this work, the soil stack was reduced in height to just above the toilet connection. The workmen assured us that the extra pipe above that point was 'useless' and cut it down for aesthetic reasons.
Since the work was done, we often had problems with the bath draining very slowly for no apparent reason.
We have recently replaced the suite again, but with a shower cubicle instead of the bath.
We are now getting problems with the shower tray overflowing due to slow drainage. (It is just an ordinary mixer valve type shower.) Cleaning the trap seems to make little difference. We have also noticed that if the tray fills up and you then stop the shower, the water will slowly drain away and then you can turn the shower on again and let it run for as long as you like without any further problems.
It is almost as if some sort of air lock has to be overcome before the drain operates correctly. Is this possible? Could this be to do with the stack?
I have read on this forum that the stack should reach above sink height. Also, as it is boxed in, I do not know whether it has an air admittance valve fitted. I suspect not. What are the symptoms of a stack with no AAV / being too low?
Sorry if I have rambled on , but this is puzzling me. Also, I am fed up with the shower overflowing and ruining the kitchen ceiling!

Any views welcome!
Thanks, Richard ('splidge')

 

[gas4you]

if this is your only stack pipe then they have done a bodge job for you. As I understand it you must have at least one stack pipe open to air, this is not just to let smells out, it is to let air in when needed as in draining a bath or flushing the toilet.

A dirgo, or AAV would be ok on an extra stub stack but I don't think it can be your only stack,

Sounds like you haven't got one anyway!

Unfortunately I can see no way other than to remove boxing to check, and then get 'well known company' back in at their cost to put right

 

[Splidge]

Thanks for your quick reply, gas4you.

Yes I think I will have to dismantle the box this weekend to check.

I will let you know what I find (or don't find!)

I don't know what a dirgo looks like, but I assume it would be obvious if it was there!

I don't think I will be able to get the bathroom company back, as it was over 10 years ago, and we have since ripped out most of their installation.

 

[holty]

i think its like this, for every fifth property on a sewage run ,four can use aavs. the fifth has to have its stack to open air. but if i was you i would check to see if you have you have a durgo if not prob just as well to take the stack to open air anyway, for good measures. do you get alot of trap seal loss e.g gurgling noises or water splurting out of them.

 

[Splidge]

I presume there must have been an aav at my property originally. It has never been vented to air. Venting to air now would be unsightly and expensive.

I do get the gurgling noises from the traps (particularly the shower and sink) on occaision.

I can see why lack of an aav may cause problems when flushing the toilet, but would it also affect the shower drain, which has a much lower flow rate?