I have an oil-powered boiler along with a water cylinder which has been installed in our home for a number of years by some previous owner. We've been here a couple of years without a hitch.

Just the other week the tundish started overflowing with water every time the boiler fired up. I called the plumber out as I know nothing about boilers or water heating whatsoever, and after having two plumbers out over two days, they eventually told me I need to call someone who clears out drainage.

I'm only just figuring out how the whole system works but I'm hoping someone can explain it a bit more for me.

From the top of the cylinder down to the tundish there's a pipe. The overflow isn't coming from the cylinder. That took me a while to figure out, and was the first thing I thought was happening. The water is actually coming from the bottom upwards. You can see in the following picture that the pipe goes in two directions. Going downwards is from the boiler, and going upwards is.... I haven't got a clue! I can't actually see where it goes unfortunately.


In the following picture you can see the whole setup, the tundish and cylinder on the left, and boiler on the right.

enter image description here

The final picture shows the pipe that goes up to the tundish from the boiler. As you can see, the pipe comes out the very top of the boiler.

enter image description here

My question is, what could cause water to come up from the bottom upwards through the tundish? Is it really a case of blocked drainage and all I need to do is get someone who specialises in drainage out?

  • I believe the pipe between the top of the boiler and the tundish is simply the blowoff drain line. Both the tundish and the boiler drain INTO this line and it should normally be dry. The other end where it goes into the wall should be a sewer or some other form of drain. – Dave Nay Jun 6 '12 at 12:29
  • 1
    You had a plumber that said you needed to call someone else to fix a drain? Doesn't sound like a very good plumber to me! – Steven Jun 6 '12 at 13:54
  • @Steven two plumbers came out over two days from the same company to tell me that. – Kezzer Jun 6 '12 at 15:09
  • 1
    I think you should try a different company! – Steven Jun 7 '12 at 15:43

Amazing it's been a month since I visited this, but I've now had four plumbers, an electrician, a drainage service company, and a previous owner of the home in to figure this out.

Fortunately, the answer lay in phoning the previous owner who was very helpful.

The outflow pipe is blocked (still) meaning that the excess water which is pumped out from the boiler, and perhaps the cylinder, can't escape to the drain. The drain is somewhere under some bricks that look as if they're cemented in, however some are loose and beneath them is a drain. Yes, you heard right, a drain under some paving.

The answer is to find this drain, which I'll find in the next couple of days, and unblock it by calling a drainage service out to use special tools to clear the pipe work. Basically when the boiler is on, the outflow pipe fills up and up until it comes back up the pipe and into the tundish overflow, leaking out all over the floor.

When in doubt, find out where your overflow goes. When you have no idea where it is, phone the previous owner.

Now I'm stuck with many plumbers bills.

  • 1
    Just some thoughts... if these are the only two things going into that drain then it could be that the drain collapsed and needs to be replaced. I am suprised that a plumber couldn't figure this out for you though, any professional plumber should have a scope that allows them to see what is happening inside of blocked drains. – maple_shaft Jul 3 '12 at 11:04
  • No, because drains are exposed. This drain is completely hidden. If you saw our patio, you'd know what I mean. It looks like the whole thing is cemented in. They looked outside and couldn't see an outflow. We looked under the path (after removing the panel) and could see it going out the wall, but nothing on the other side, thus it seemed like it went into the ground. – Kezzer Jul 3 '12 at 11:52
  • I'll try and take pictures when I find it. I haven't found it yet though! – Kezzer Jul 3 '12 at 11:52
  • 1
    Thanks for posting the answer. I still think the plumbers that came out sort of screwed you. They should have a camera with a locator on it, so they can feed it down into the drain and then use a probe to see where it goes. Hidden or not they should be able to find it - almost all pipes and drains are hidden after all! – Steven Jul 3 '12 at 14:46
  • No you're right, they did screw me over! We've dug up an area of sand under the patio. It's the only area under the patio which is sand, a strip about 3 foot long by half a foot wide. This certainly ties up with being an outlet, but we haven't yet found the pipe. More work going on tonight. – Kezzer Jul 5 '12 at 14:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.