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New washing machine overflows waste water pipe

edited August 2009 in Troubleshooting
A few months ago I had to buy a new washing machine. The previous washing machine came with the house, a new build, which I bought 10 years ago.

The two odd things, to my mind, about the new washing machine are that it only takes a cold water feed and it seems to use much less water than the old machine. I have been informed that this is the case with most modern washing machines.

The problem is that when the machine is expelling the waste water the waste water pipe overflows. The first time it happened I removed the u-bend bit of the washing machine waste pipe and removed something the size of half a golf ball . I also poured a lot of Mr Muscle drainage blockage down the kitchen plughole.
This seemed to do the trick but very quickly it started happening again. I have checked the u-bend bit of the waste pipe and it is clear. Yesterday I managed to insert one of those long wire pipe clearing thingies at least 10 feet down the waste pipe. The first wash today no overflow but the second resulted in about half a pint overflowing.

I have a couple of theories as to why this is happening with the new machine when it never happened with the old machine.

1. The old machine expelled more water which had the result of preventing waste stuff accumulating in the pipes and causing a blockage.

2. The pump on the new machine is more efficient and pumps the water, even though it is less volume, at a rate that the washing machine waste pipe is not able to handle.

I was wondering if anyone on here has installed a new modern washing machine recently and if they have had similar problems with the waste water pipe overflowing. Are there any DIYers with tips on how I can solve this problem without having to call in a plumber?


  • I'm no expert, but I've had troubles before. Two things worth trying (if you haven't already):
    1. Make sure that the washing maching outflow pipe is pushed right down inside the drainage pipe by a foot or more - the further it's in the better ;-)
    2. Get yourself a flexible coil ramrod thingamy to push through the drainage pipe and clear any blocks.
  • Sounds like you may need a non return value on the outlet pipe.
  • The out pipe on the new machine is less chalked up so water is dumped out quicker?
  • If possible, extend the vertical waste pipe by quite a bit, therefore allowing its capacity to increase.
    Most modern machines already have an internal non-return valve, so perhaps you could try a permanent watertight fit to the waste pipe?
  • Thought it might be useful to let people know my solution to this problem.

    I went to my local plumbers merchant shop with the intention of buying a Non Return Valve for the waste water pipe. However, the shopkeeper advised against fitting a NRV as this could result in damage to the washing machine if the valve closed whilst the machine was expelling waste water. He said I should focus on clearing the blockage and asked me what I had done. I told him about pouring Mr Muscle drain cleaner down the waste pipe and he laughed saying that is ok if you want to waste your money. He suggested something called Amo Kleen Knock Out, an 'Industrial Strength Product for Trade and Professional Use'. I bought a litre for about £5.50 and went home and poured about a pint down the waste pipe. Within seconds I heard all sorts of gurgling and and hissing noises and the pipe became extremely hot to touch. I left it about an hour and then put on a hot wash, as advised, to wash away all the debris that the liquid (which is basically solphuric acid) had broken down.

    No problems since!
  • I've had the same problem. I put it down to a few of things;

    1. Washing detergent and washing residue solidifying in waste pipe
    2. Waste pipe insufficient diameter.
    3. Bends in waste pipe restricting flow.
    4. Wife using washing machine not to manufacturer’s specifications.

    My solution is, to rip the kitchen out and build an extension with waste pipe 4 inches in diameter X 1 metre long and me to take a more active role in domestic matters.
  • [cite]Posted By: charltonkeston[/cite]and me to take a more active role in domestic matters.

    Or trade the wife in for one that knows how a washing machine works?????
  • [cite]Posted By: Stu of HU5[/cite]
    [cite]Posted By: charltonkeston[/cite]and me to take a more active role in domestic matters.

    Or trade the wife in for one that knows how a washing machine works?????

    Stu one of the rules of life is; No matter what you do for a living, hobby or however complicated your lighting system is, never tell your wife you know better than her on the washing machine subject, even if it is blindingly obvious that you do.
  • Amen to that CK !

    Add ironing to the list of no-go-topics as well - even though it takes about 5 seconds to empty the water out at the end of a "session" and so avoid all sorts of crap coming out next time she's doing my shirts, it is best to never mention this.

    As for dusting - the laws of gravity dictate that you should start at the top of the bookcase, not the bottom, and so eventually push any dust all the way to the floor....but it is a subject best not ventured into
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