HOW TO DRAIN DOWN HEATING SYSTEMS – GRAVITY FED – Plumbing Tips

Posted on: February 7, 2017 by in Plumbing Videos
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HOW TO DRAIN DOWN HEATING SYSTEMS – GRAVITY FED – Plumbing Tips


This video explains the basic process of draining down a gravity fed heating system. We cover turning of the water supply, turning of the electrical supply and finding a suitable drain cock to attach your hose to. We also cover venting the system so you can have a go yourself

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I’m gonna show you very very quickly how to drain down an F and E heating system. That means a feed and expansion heating system. Which mean that you’ve got a little tank in the loft that supplies water via a ball-valve, down into your heating system, okay? We’re also then going to do a very very quick video after that about how to fill up an F and E heating system. So this doesn’t work for pressurized systems or combi-boilers. So the first thing you’ve got to do is make sure that the heating system is switched to “off”, alright? We don’t want the heating system lighting up while we’re doing all of this.

So make sure it’s fully isolated first. Now, we go up into the airing cupboard that we’ve got here and you’ll often find that you’ve got a system that looks a little bit like this but can always be laid out a little bit differently. Now the most difficult bit about actually draining down one of these systems is, sort of, ascertaining what bit to turn off, and what bit of the system is what. What we’ve got here, this is the coil feed from the boiler, okay. This has got hot water going in from the boiler, into this coil here, and going out again. Now this pipe here is the expansion pipe that goes up and over into your loft tank. This pipe here is the feed at the bottom of the tank that goes down into the system. So we need to turn this pipe off here.

Often, where this pipe joins the main part of the central heating system, you can get little blockages. So when it comes to filling up again that might be something you want to think about, if you have trouble filling it up. If you do, then let us know. Basically, I’ve turned this one off here, but if you don’t have a valve, you can go up into the loft, find the small tank, and tie the ball valve up. It’s really easy to do, just get yourself a little bit of string, tie it around the ball valve and tie that up around a rafter, or even on a stick that rests over the top of the tank, and that’s to stop any water coming in from your mains.

If you can’t do that, the last think you can do is actually turn the main supply off to the house, which’ll in turn, turn the supply off to the ball valve, which means then that the system will drain down when you come to drain it. So, we’ve got that turned off now, so now I’m going to pop downstairs and find the lowest point that’s got a drain off on it, pop my hose on it, pop a towel on there, and start draining down! Right, so I’ve hunted round the house, and I’ve found that this drain-off here is the lowest drain-off on the system. It’s on the ground floor, as you can see it’s only about an inch off the floor, and also, it’s not a drop-down leg as well.

So make sure this radiator, sometimes you can have rads that are fed from two pipes that come down, which means that all you’re going to do then is just drain down the top floor, and that one leg. If you work on other radiators on the ground floor, they might not drain down. So always be aware, trace out the pipework, and make sure that you’re actually going to be draining down the whole system.

So what I’ve got to do now is just grab a hose, put a little towel under here cuz these can leak around the outside, which is a bit annoying, and then turn it on, and then we can think about then venting the radiators. We’ve got to think about health and safety, haven’t we! Cuz that’s the culture we live in these days! I’ve got a beautiful, white towel that a customer has given me. Sometimes you might lock a little jubilee clip, this is a nice, fresh, tight hose, so should be fine. And then, we’re just gonna get a small spanner on here, and undo this, okay? We’re gonna turn it anti-clockwise to turn this on. Turn that on and you should start to hear water rushing out of here. There we go.

Bit of water coming out now, can hear it. Right, so as you see, our hose is going off and outside, out to a drain at a lower point. So as you can see, we’ve now got water coming out of our pipe just here, great. Right, the thing is, though, is we’ve obviously turned this off here and we’ve got water coming out of our hosepipe downstairs. Effectively, though, what we’re doing at the moment is kind of putting a little vacuum on each of the radiators.

We’ve let the water out of the tank up there, also this F and E pipe would have also emptied, but each one of the radiators is now going to need its little air vent at the top of it opened up.

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