Sink Water not Draining, No Blockage

[Bannerman]

Water depth is not the issue. This situation is similar to an air bubble within a hydronic heating system that is preventing hot water from flowing through a radiator. Even as you might expect the pressure from the circulator pump will be sufficient to push the air bubble forward, that is not often the case so bleeding the air bubble out from the radiator becomes necessary.

As there is nowhere for the gas to be vented from the highest point of the drain line after the trap, results in a flow restriction. As proven by the temporary small vent tube pushed past the trap, a vent located where the trap arm intersects the drain elbow within the wall, will ensure gas will not be trapped at that location so the small amount of gas trapped where the trap intersects the trap arm, will then be more likely be pushed forward by the weight of the water draining from the basin.

 

[Bannerman]

Peter, your drawings show the trap arm as level running back into the wall, but from the photo in post #1, the trap arm appears as though it might be running uphill toward the wall. This appears to be confirmed by the angle of the trap arm for the old trap shown in post #16. If the trap arm is actually level, I would expect it to be at a right angle where it intersects the old trap barrel. If there is an actual uphill slope, that will only cause additional gas to become trapped within the drain line.

 

[Sponsor]

 

[Bannerman]

FYI.

https://images.app.goo.gl/RvVurDvfiAR5AEBVA

 

[WorthFlorida]

If your drawing of the drain system is correct, I see the drain past the wall rises and it's causing a second trap. Two traps will not drain. As Reach suggested, the down pipe from the sink basin may have been modified where pipe was cut above the lower part of the trap arm thus no trap effect. Look inside the old trap.

https://www.amazon.com/Chrome-Bathr...t=&hvlocphy=9053023&hvtargid=pla-854152501351

 

[Peter Dolan]

Thanks for all the responses guys;

Your latest trap drawing in post #16, shows a pointed section which is above the trap arm. I suspect that raised section will trap a large bubble of gas which will prevent the water to pass by below the bubble. This will be similar as shown in your previous drawing within post #9 above.

This is just a crude drawing showing where I took the current trap pieces from, (they were spares) the red pieces highlighted in that drawing are now inverted and make up the trap you can see in the photo and diagrams.

The only way I could see trapped air stopping flow is if there is some really big belly in the drain line farther on after the wall entrance. The more I think about it, this matches the symptoms.

I've no idea how it is after the wall, but I'd be happy for there to be a hidden belly that already acts as a trap! Then I don't need to bother too much with this one!

Peter, your drawings show the trap arm as level running back into the wall, but from the photo in post #1, the traparm appears as though it might be running uphill toward the wall. This appears to be confirmed by the angle of the trap arm for the old trap shown in post #16.

I can confirm that the trap arm is level/horizontal, it's just the angle of the picture that makes it look like that. The old trap was also level but I didn't put it back together properly for the photo, sorry about the confusion!

If your drawing of the drain system is correct, I see the drain past the wall rises and it's causing a second trap.

Well I HOPE that drawing is correct, as it will mean that I don't need to worry about this trap so much... but the modification for that drawing there is by Reach4 just as a suggestion as to what might be past the wall. Unfortunately I don't know for sure.

Look inside the old trap.

I have just checked inside the old trap, the interior pipe as you described in your diagram isn't there at all, and although I removed the old sink about a year ago I don't remember there being any pipe connected to the plug/drain that would have run inside the trap as per your diagram so I believe you are right that it was indeed modified and was in fact removed completely, probably for this exact same reason. Unfortunately I cannot ask as the sink has been there for so long nobody knows when or by who it was installed.

As far as I see it I reckon I am pretty safe from any sewer gas, we are on the first floor (one above street level), the drain has been open for a year at the wall anyway and I suspect it has always been the case that the interior pipe in the bottle trap was never there, therefore also technically open to the room. This leaves me two options I guess, either put my own vent into the existing trap just before the wall or purchase another bottle trap (the old one is knackered) and remove the interior pipe on that...

 

[Reach4]

I've no idea how it is after the wall, but I'd be happy for there to be a hidden belly that already acts as a trap! Then I don't need to bother too much with this one!

It conforms to both your observations and the laws of physics.

 

[Peter Dolan]

Well, just in case there was anyone hankering for an update on this, I have put a vent into the pipe and the water is now flowing. It's still getting backed up a little bit, so there is either a physical blockage further down the pipe as well or there is more pressure further down the line. Either way it now works and I can put an end to this whole sorry mess. Thanks for all the help guys!