Unusual waste issue with air con combining waste pipe in an old home

[dy1]

Hi
I live in a 400 year old stone house and these properties, as many will know, are always a compromise when installing modern plumbing/electrics etc.

I have a room in the house that has a split system air conditioning unit. The drip feed hose joins the main outlet to drain which it shares with dishwasher and washing machine waste. I never run washing machine and dishwasher at the same time in order not to overwhelm the waste pipe.

Recently when the dishwasher performs a drain, water has travelled up through the waste pipe up to the air con drip waste hose , which is about two meters long, and then spurted out at some pressure the air con unit when the unit is off. There is a good fall off on the air con hose. It’s only one spurt generally. It felt like air pressure was responsible. Im only guessing here

The original setup had a u bend trap at the bottom of the down pipe in the enclosed pic before it turns to the left and heads towards the main drain.

Steps taken

I called in an air con specialist who checked that the drip tray in the unit was not compromised and pipe was clear, and that the air con wasn’t causing the issue. He gave it a clean bill of health.

I then put a strong drain clearing product in to make sure there was no blockage in the waste. We took it to bits and also found no blockages. There was obviously water in the U bend/trap. We decided to try a non return valve in line further up the waste pipe and dispense with the U bend.

Running lots of dishwasher cycles to test there have been no further spurts of water out of the air con unit however I can still hear gurgling coming from the air con pipe at the unit end so Im nervous about it. Also there is a waste smell in the area the pipe work photographed resides. I was hopeful the non return valve might be ok by itself but Im looking for some ideas. Should I put the trap back in?

 

[MeldrewsMate]

Is your a/c unit high on the wall? Does its condensate discharge into the top of the white tee?
How far does the wastewater have to travel horizontally from the base of your photo to the main drain (outside?)
In your photo which machine discharges into the high connection at the tee, and which to the lower connection?
Is the a/c condensate collection tray open to the atmosphere, and does the discharge from the tray flow continuously down to its discharge connection?
What are the arrangements to allow air to enter your discharge pipework?

Ideally each discharge pipe should have a u-bend trap to prevent foul air returning to each appliance, this includes the a/c condensate discharge.
There should also be an air admittance valve located above the white tee (it lets air in but not out).

MM

 

[dy1]

Is your a/c unit high on the wall? Does its condensate discharge into the top of the white tee?
How far does the wastewater have to travel horizontally from the base of your photo to the main drain (outside?)
In your photo which machine discharges into the high connection at the tee, and which to the lower connection?
Is the a/c condensate collection tray open to the atmosphere, and does the discharge from the tray flow continuously down to its discharge connection?
What are the arrangements to allow air to enter your discharge pipework?

Ideally each discharge pipe should have a u-bend trap to prevent foul air returning to each appliance, this includes the a/c condensate discharge.
There should also be an air admittance valve located above the white tee (it lets air in but not out).

MM

Hi MM
Thanks for your message.

Air con unit is higher than the hose . I have annotated in red which feed is which on the pic. The air con does not produce large volumes of water. The spurting issue has only happened when the machine is not in use. Air con is the top grey hose as annotated. dishwasher is far lower (second grey hose near bottom) . The waste only travels to the end of the pic horizontally - there is a fall off .....There are no arrangements for air discharge.

Which white T should the air admittance valve be above?

 

[endecotp]

Your dishwasher is now connected below the trap, which is bad.

It seems to me that there must be a blockage or constriction downstream of what you have shown.

 

[dy1]

Your dishwasher is now connected below the trap, which is bad.

It seems to me that there must be a blockage or constriction downstream of what you have shown.

Hi - That was done as water/air was forced upwards when the dishwasher flushed out to the grey hose above. Thss is a small amount of water that came out in a single spurt at pressure. Theres no blockage - it's been taken to bits and checked twice in the last week. It's no longer happening following the non return valve addition. Theres gurgling and a localised smell now which needs addressing.

 

[MeldrewsMate]

You've answered some of my questions, please have an attempt at the rest.
You have only one white tee that I can see, at the top of your photo.
If every outlet has a trap then foul air cannot escape and cause your drains smell.
The not return valve causes a small backpressure when the dishwasher discharges, possibly blowing a small amount of water back towards the a/c. The AAV is to stop the discharged water pulling the sealing water out of upstream traps.

 

[dy1]

You've answered some of my questions, please have an attempt at the rest.
You have only one white tee that I can see, at the top of your photo.
If every outlet has a trap then foul air cannot escape and cause your drains smell.
The not return valve causes a small backpressure when the dishwasher discharges, possibly blowing a small amount of water back towards the a/c. The AAV is to stop the discharged water pulling the sealing water out of upstream traps.

Hi
The lower connection is the dishwasher. The A/C collection tray is within the wall unit. It's not visible without removing the housing and even then you would have to take it to bits to access it but there is a hole that feeds drips it to the outlet. It is not sealed. The air con engineer checked the flow of the tray that spans the width of the unit very carefully.- I am not sure of the drain run under the house.

There is a second tee further down where the dishwasher feed is marked in red.

I think that covers everything you have asked me....

Since the non return valve was installed there have been no further spurts however its gurgling and as we removed the trap which was at the bottom of the right hand pipe before the elbow turns left, there is a smell now. I can't see how a trap could be fitted to all those connections in the space. I can reintroduce the trap and add an air admittance valve?

 

[MeldrewsMate]

Here is a summary of your situation as I see it.
The dishwasher discharges warm water which contains biological material (food for bugs).
Bugs produce drain smells as they consume the food kindly provided.
Bug farts rise with the warm air in the drain, emerging at the aircon drain tray.
The aircon fan blows these stinks around, or they just diffuse into the room.

Does that scenario fit with your exoerience?

The solution is to use traps to stop the foul air escaping the drain, and an AAV to stop discharging water sucking the water seals dry.

 

[dy1]

Here is a summary of your situation as I see it.
The dishwasher discharges warm water which contains biological material (food for bugs).
Bugs produce drain smells as they consume the food kindly provided.
Bug farts rise with the warm air in the drain, emerging at the aircon drain tray.
The aircon fan blows these stinks around, or they just diffuse into the room.

Does that scenario fit with your exoerience?

The solution is to use traps to stop the foul air escaping the drain, and an AAV to stop discharging water sucking the water seals dry.

Hi
The scenario is close buy not quite correct in that the air con is off when these smells happen. The odur is to do with the piping and removing the trap

I have updated the piping to include an air admittance valve on the branch where the air con drip is located. I have reintroduced the trap at the bottom but now with another air admittance valve. Smell has now gone, and there was no blow back/spurt through the air con when I ran the dishwasher. However this morning I ran the washing machine and when that emptied I had a single spurt out of the air con unit. There is no room to add a trap to every device. I have today ordered two non return valves for flexible hoses for both dishwasher and air con feed. They will be here tomorrow. I would have thought that might stop it. Im enclosing an up to date pic of the changes...

 

[Hugh Jaleak]

How is the Washing Machine connected, it's not visible in the pictures?

Needs to be an air break where the Pumped appliances connect, I'd wager the washing machine is also on a sealed connection, you've a blockage downstream in the waste pipe, and when either the washing machine or dishwasher pumps out, the water cannot get away quickly enough and is blowing air and water back up the line, which is then exiting via the only route possible, the Air Con Unit.

Get rid of the AAV's they'll do nothing to help this situation. The issue is with positive pressure, not negative, as the water cannot get away quickly enough and is effectively trying to enter a sealed chamber, so is looking for a way to displace the equivalent volume of air from within that chamber.

Fit a Standard open standpipe, connect Washing machine and Dishwasher at the top using a McAlpine V33WM https://www.bes.co.uk/mcalpine-appliance-twin-connector-11-2-or-40mm-25172/ Couple your Air Con drain in just below the top using a Tee. Ensure the waste pipe is clear along it's full length, and there are no dips in it where water/crud can collect.

 

[dy1]

How is the Washing Machine connected, it's not visible in the pictures?

Needs to be an air break where the Pumped appliances connect, I'd wager the washing machine is also on a sealed connection, you've a blockage downstream in the waste pipe, and when either the washing machine or dishwasher pumps out, the water cannot get away quickly enough and is blowing air and water back up the line, which is then exiting via the only route possible, the Air Con Unit.

Get rid of the AAV's they'll do nothing to help this situation. The issue is with positive pressure, not negative, as the water cannot get away quickly enough and is effectively trying to enter a sealed chamber, so is looking for a way to displace the equivalent volume of air from within that chamber.

Fit a Standard open standpipe, connect Washing machine and Dishwasher at the top using a McAlpine V33WM https://www.bes.co.uk/mcalpine-appliance-twin-connector-11-2-or-40mm-25172/ Couple your Air Con drain in just below the top using a Tee. Ensure the waste pipe is clear along it's full length, and there are no dips in it where water/crud can collect.

Thanks for chipping in

The washing machine waste is marked at the top . The machine is on the floor above and travels down the 40mm pipe. Following fitting the AAVs the gurgling that was in the system has ceased so there is some benefit. Ive today received a true design 3/4" non return valve which are supposed to be the bees knees. I've cut into the air con hose, however there is a small weep from the connection which I will look at tomorrow. Oddly water appears on the air con side of the non return valve which I can't understand as the air con isn't on and the pipe was dry when I cut it. This happens now when the dishwasher is offloading waste, not the washing machine. It appears to be travelling up through 2x non return valves. Theres no blockage . Only a trap ....Its confusing . On testing there was no more spurting out the air con (when it's off) however given there's weeping im not convinced this is sorted. You can't see the inline non return as there's only a black ring visible Ive taken a pic

 

[endecotp]

Theres no blockage .

Prove it.

 

[Hugh Jaleak]

The washing machine waste is marked at the top .

Yes, but how is it connected? Photo would assist here.

I've explained, using my nearly 40 years of experience, what I think the issue is, but if you know better, please carry on.

 

[MeldrewsMate]

Get rid of the AAV's they'll do nothing to help this situation.

The AAV was suggested because my advice was to add a trap to the a/c discharge. Without that (and on a compromised drain) the washing machine discharge would fill the 40mm horizontal discharge pipe (of unspecified length or fall) and suck down the new trap, once again allowing foul air to escape via the a/c drain tray.

 

[Hugh Jaleak]

The AAV was suggested because my advice was to add a trap to the a/c discharge. Without that (and on a compromised drain) the washing machine discharge would fill the 40mm horizontal discharge pipe (of unspecified length or fall) and suck down the new trap, once again allowing foul air to escape via the a/c drain tray.

Therein lies part of the issue, the 40mm waste pipe is, I suspect, filling very rapidly when the Washing machine and/or Dishwasher discharges, and once full, it needs to start displacing air as currently it's a sealed unit.

That in itself is wrong, needs air behind the water, so an air break is needed above the discharge point, which the AAV could provide, but in this case, it's trying to vent the air trapped in the pipework, and the only way out is through the air con drain. The AAV will let air in but not out.

Same scenario as those who say their WC backs up when it's flushed, or they're getting gurgling and foul smells from a shower when the WC is discharged, invariably the stack is capped with an AAV, it's blocked underground, and so the 6-9litres from the WC needs to try and displace the equivalent volume of air, so looks for the easiest exit.