Strange toilet flushi

[maxwead]

I have 3 Ideal Standard (Alto I think) dual flush toilets. One is fine and flushes perfectly. The other 2 have the same problem; when flushed the water is release from the cistern and the paper etc is removed from the pan, but almost immediately after the flush has finished the water rises back up the pan about an inch. The water is clear and everything has been removed, just this small "backlash". Also sometime later the water in the pan becomes discoloured as if some waste were seeping back into the pan.
I have checked the inspection covers outside the house and water flows through when the toilets are flushed, so there cannot be a major blockage.
The 3 toilets share a soil pipe (vent pipe ?) so as one toilet is working OK I do not think the problem lies there.
I have tried caustic soda and other such unblockers but with no luck.
Any ideas would be much appreciated. Thanks a lot.

 

[WaterTight]

Is the flush a bit weak and watery?...For want of a better expression.

 

[maxwead]

No, the flushes in all 3 toilets are the same; plenty of water with plenty of force. As I said, the flush does enough to clear the waste and empty the pan.

 

[WHPES]

Sounds to me like pressure difference caused by hydraulic vacuum on flushing in the soil pipework. Where are the other toilets located? Are they connected properly to the soil stack or piggybacked together? Is the soil pipe vented / air admittance valve?

 

[maxwead]

The working toilet is on the ground floor, the 2 with this problem are on the 1st and 2dn floor. I'm not sure how they are all connected to the soil stack as the pipes are all internal and thus bricked up. The soil pipe goes up into the loft and then out through the roof; I can see no sign of an air admittance valve, should that be in the loft as well or will it be lower down the pipe. In case it's relevant, it is a Redrow town house built about 6 years ago.

 

[WHPES]

If the soil pipe goes out of the roof then no AAV is needed

Is it possible to fit a branch ventilating pipe to each of the WCs

 

[Paulus]

The first thing I would try is plunging the toilets on the first and second floors, sounds like there could be a partial blockage in soil pipe between ground and first foors.

 

[mcvince]

Have you tried hiring or contacting a professional? maybe the pipes are rusted?

 

[maxwead]

I think fitting a branch ventilating pipe would be way beyond my expertise. I was hoping to avoid any alterations to the actual pipework as it means a lot of work dismantling the house as the pipes are all concealed. If this is what is needed, isn't it something that should have been put in when the house was built ?

 

[maxwead]

I have plunged both toilets on a fairly regular basis off-and-on over a period of 6 months or so, with no luck. Maybe I need a larger plunger or stronger arms