New basin won't drain

[kevinti28]

Can anyone help with a problem concerning a new basin which doesn't drain? I remove my old basin from the bathroom (a wall mounted basin which drained o.k. except for the occasional blockage due to hair/sludge etc)) and replaced it with a basin which sits on a wooden vanity unit. The new basin has a pop-up waste unit and I connected it to the old 32mm pipework. Due to the new basin waste outlet being about 40mm higher than the old I have had to use a number of 90 degree bends to get the pipework to connect up (I couldn't use a telescopic trap as the shelf in the vanity unit would have been hard up against the trap). When I turn on the taps without the pop-up waste in place, the basin slowly fills up, if the basin has about 75mm of water in it, it takes about 3 minutes to drain away. So I have tried the following:
1. I removed all of the pipework, extended the waste connection to the outside of the unit and put on a bend, then I used a funnel and poured water into the waste pipe, it flowed away without any problem (so no blockage).
2. I installed the trap (a shallow bottle type) and with a bowl under the outlet I turned on the taps, the water flowed straight out of the basin without any problem.
3. After reading the forum I installed an anti-vac valve to the outlet of the trap, after connecting up the pipework and turning on the water, the basin starting filling up again and then water came out of the anti-vac valve! I tried another valve in case this one was faulty, same problem.
4. I changed the bottle trap for a p trap, same problem.
5. I installed a tee piece into the pipework at the wall, then I connected the basin to one branch of the tee and then extended the other branch with some pipework as high as I could within the vanity unit to try and allow some air into the waste pipe, turning the taps on resulted in the basin filling up and the temporary pipe filling up and overflowing.
7. I have tried everything I can and am now asking for some help, please .......... (sorry for the long post but I wanted to describe everything I have tried)

 

[Softus]

Interesting one.

I have a hunch that this has more to do with where the 32mm pipe goes after the wall connection.

Do you know, or can you see?

Does it enter a soil stack?

Does it have the correct gradient?

Is the soil stack vented?

 

[kevinti28]

The waste goes through an internal blockwork wall and turns 90 degrees, it then slopes down at about 15 degrees before turning through 90 degrees again and passes behind the hot water cylinder, there is a connection behind the cyclinder which takes the drain from the central heating boiler, I don't know if it is a straight tee or if there is a trap between the boiler and the tee, the pipe then goes through another blockwork wall and connects directly to the soil pipe, which is vented. The boiler drain is an open pipe with a short length of 22mm copper in the end. None of this pipework or the boiler connection has been altered before or after fitting the new basin.....

 

[Softus]

Next hunch...

Am I right in thinking that the old basin had a overflow built into the casting that drained into a slotted waste?

And am I right in thinking that the new basin has no built-in overflow at all, and that the waste is unslotted?

If so, you have an air lock in the 32mm waste, and the AAV that you tried out won't help, because it won't allow air to escape.

This can be caused by waste pipes if they run uphill for a short section, even if the rest of the run is downhill. Are you able to check whether there is a constant 'fall' (i.e. downhill gradient) for the entire run of the 32mm waste?

Also, you should check the overall length of the run - 3 metres is a practical working maximum for a straight run; when measuring yours I would add 200mm for each 90° elbow and 100mm for each 45° bend.

If greater than 3m then an upgrade to 40mm is necessary.

 

[buck51]

Hi you said you used a number of bends to connect up to waste fitting which is 40mm higher
How many did you in fact use and do any of them face down and then back up if so you have in fact created a double trap
Other than that all I can think is you have a blockage try a plunger but get some body to plug the connection where the boiler 22mm copper enters
and the over flow
PS is it a condensate drain or a safety valve outlet

 

[kevinti28]

Softus - The old basin did have a cast in overflow, the new basin has a slotted waste with a plastic pipe connecting the overflow to a banjo fitting. The run is about 1500 mm of straight pipe in total with 5 no. 90 bends, so at 200 mm each that gives 2.5m so hopefully that should be o.k. Unfortunately I can't check the pipe behind the cylinder to see if there is a fall, as I can't get a level in the gap, so I'll try measuring from the pipe to floor on either side of the cylinder.

Bucks51 - The pipework between the waste outlet and the wall is very short, 3 lengths of pipe each about 100 mm long with 3 bends all going downhill without any backfall. The boiler drain is for the condensate, the safety valve pipework goes through the outside wall.

I'll try a plunger and also to check the fall on the pipework, before replying, many thanks so far ....

 

[kevinti28]

Softus and Bucks 51, I checked the pipework and it all seemed to go downhill, eventually I bought one of those drain unblockers which has a large cylinder. Blocking all inlets I used the unblocker, after 5 tries there was a loud gurgle and the sink drained - hooray. So it must have been some sort of blockage after all. Thank you for your suggestions.

 

[Softus]

That's good.

Do you have any clue as to why the problem wasn't evident with the old basin in place?