We have a mysterious water ingress into our gas-fired boiler. We eliminated rain as the source so the only two options seem to be the condensate pipe backing up, or ingress from the gas supply line itself.

We've a plumber engaged to solve the mystery and figure it out but I was curious, is water in your gas supply actually feasible? And if so would it imply a supply fault or something in our own pipework?

I know plumbers pressure-test after any work to ensure no leaks and my thinking is if there was water ingress on our pipe that must imply a leak. Could one really have water in the mains gas supply or is that vanishingly unlikely? How would you reliably determine this if it were a possibility?

  • 1
    #3: "boiler" is wetting itself.
    – Mazura
    Commented Nov 12, 2022 at 1:36
  • Indeed, a leak in the heat exchanger is the first most likely option here.
    – Ecnerwal
    Commented Nov 12, 2022 at 4:23
  • @Ecnerwal that is an interesting point, thanks
    – Mr. Boy
    Commented Nov 14, 2022 at 8:44

2 Answers 2


Water in natural gas lines can indeed be a problem, and it's a supplier issue in my experience.

I once lived in a place that was at a low point in the line, near the end of the line, and had several interruptions in gas service due to the line filling with water, which was eventually addressed by the gas company doing something out in the street. First they pumped out water from something out there a few times, and the problem recurred, so they showed up with more trucks and dug things up, and whatever they did then seemed to resolve the problem for good, or at least until I no longer lived there.

  • 1
    How would you reliably determine this? None of your shit works and then a bunch of trucks show up and it works again, +1.
    – Mazura
    Commented Nov 12, 2022 at 1:37

Natural gas is humid when retrieved from the Earth. If that moisture is not removed properly then it ends up causing issues in the supply lines.

To test if your supply line has water then shut off the gas and uncap a sediment trap and check for moisture. It might technically be a "drip leg" depending on the installation orientation.

Chat with your neighbors and see if they're experiencing similar issues.

However, "condensate pipe backing up" gets my vote as the source of the problem; especially if you're seeing puddles of water on the floor instead of corrosion at the burners.

  • We have no neighbours; the plumber is trusted and as keen as we are to get it fixed :) I have not heard of a "drip leg" so will have to look for that.
    – Mr. Boy
    Commented Nov 11, 2022 at 17:48
  • 1
    @Mr.Boy Well that's good to hear, I'll remove the faulty conjecture =). The drip leg could be called a sediment trap as well and it's usually installed fairly close to the gas appliance. Make sure you shut off the gas before uncapping it!
    – MonkeyZeus
    Commented Nov 11, 2022 at 18:32

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