I have a new washing machine (there wasn't one there before as I've recently moved in). When the machine is running the water spouts out particularly through a vertical 'vent' hose leaving a small flood.

I've cleaned the parts out and even tried to buy new piping from Screwfix and B&Q (they didn't fit together) as I thought I could just get away with no 'vertical vent' as I've never had one before. i paid money for Hotpoint to fit the washing machine but the guy just said it was leaking and he hadn't seen plumbing like that before.

How can I resolve the problem myself without waiting on a plumber?

under cabinet image showing drain line with AAV

  • Welcome to Home Improvement. I've edited your question to include proper punctuation and to actually ask a question. When you take the tour, you'll note (among other things) that this is a Question & Answer site, so we expect there to be an actual question asked.
    – FreeMan
    Commented Mar 1, 2022 at 14:08
  • 1
    While you're under there, you may want to take a look at that ground cable. In the US, there are requirements for both securing and protecting cables. Having a single cable flopping around like that wouldn't pass code here. I'd imagine it's the same in the UK.
    – FreeMan
    Commented Mar 1, 2022 at 14:50
  • 1
    Additionally, I would try to clean out that drain line as well as possible. From the photo, it appears that that line is at least partially blocked, causing the water to back up and leak out the AAV. If you don't have a plumbing snake, you can buy cheap plastic ones, or even use something like a piece of wire or tubing to shove down that line and push out the accumulated fuzz/lint/hair, etc.
    – Chris O
    Commented Mar 1, 2022 at 18:00
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    On a side note, the hot water supply appears disconnected. Is that how the installers left your washing machine?
    – nogasbiker
    Commented Mar 1, 2022 at 20:06

2 Answers 2


That "vertical 'vent' hose" is exactly that. It's called an Air Admittance Valve (AAV)*.

The purpose of the AAV is to allow the line to drain properly when a regular vent line cannot be installed through the roof. The drawback to AAVs is that they fail. It seems that yours has. The suggested course of action would be to replace the AAV.

I believe that B&Q is your equivalent to one of our "big-box" home improvement chains like Lowes or Home Depot. They will probably have an AAV that will work as a replacement. Yours appears to be permanently connected to that bit of flexible pipe, so unscrew the lock ring at the bottom of that pipe and take the whole thing to the store with you. The goal is to find one whose opening is the same diameter as the one you brought with you and isn't much taller, since you don't seem to have much additional head room under the cabinet. I can only imagine that your screw fittings will be standardized as ours are in the US, so the threading on the new one should match up with the threads on the old one.

When you get home, simply screw the new one on. If you have a bit of leakage around the threads while the washer is draining, screw it a bit tighter. If you have to get out a wrench, do not turn it with a wrench more than about 1/8 of a turn! These fittings are designed to seal when hand tightened, so anything more than that won't help and will only cause additional damage. If you can't get it to seal, ask a new question about how to stop that leak.

Additional note: in the US, at least, there are very specific requirements for where an AAV can be installed and how it must be installed. I'd presume the same is true in the UK. I'd recommend checking your local regulations just to be sure your installation was, and remains, code compliant.

*This was the first link I found that seemed like it was just an explanation and wasn't really trying to sell anything. No relationship with the linked page.


As a last resort replace the Studor AAV valve, it has a check inside to prevent water etc from escaping. When you remove it you should be able to see what caused it to fail. Before doing that check your local code and the washer manual, it will probably require a standpipe with a minimum height of 36 inches from the floor. Your washing machine manual should show the requirement. Placing your standpipe too low or too high can cause backflow and overflow.

  • Isn't this basically what I already said?
    – FreeMan
    Commented Mar 2, 2022 at 15:14

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