Posted by in Plumber Talk, on August 11, 2017

This video covers the basics of draining down your heating system to fix leaks, change radiators and move boilers etc. It covers isolating the water supply, venting the system, how to find your drain offs and radiator drop down legs, re filling the system, venting of air and inhibiting.



This switch here turns it off, alright? That’s the heating system off. We don’t want it coming on or anything like that while we’re draining down. The last thing we want is the boiler lighting up, or the pump coming on. It could burn the pump out, it could overheat the boiler and crack the sections. So the first thing you do is make sure that the heating system is switched off. “Ah, but James,” I hear you ask in your stupid voice. “How does that pressurised heating system work?” “Well, y’know, I need a basic knowledge of them to know how to drain one down.” Well, usually, you’ve got your boiler, your pump, any valves: you could either have a three-port valve there or a couple of two-ports. In this system, we’ve got two two-port valves.

Then you’re going have your coil going into your cylinder, if you’ve got one; if not, a combi system. Then also you’re going have your radiators, blah, back to the boiler, blah, back to the boiler. Now, some heating systems use a gravity feed in the loft to actually push water down, via gravity, from a tank up there with a ball valve in it down into the system. But nah, we don’t have that on a pressurised system. ‘Cos we ledges, aren’t we? Yeah. Basically we have a cold water main come in, comes in, goes through a filling loop into what we call the manifold that’s often at the bottom of the expansion vessel, So we’ve a big expansion vessel like that. So you got that, filling loop, braided hose. You have a non-return valve there, a valve there. This braided hose is removable, so the system doesn’t automatically or accidentally fill up off the cold water main, which could pressurise it, which could bulge radiators, which could cause your whole world to come falling down. So yeah, there we go. That’s the basic gist of how they work.

The water heats up, expands into this expansion vessel. Like I said already, go to our video on pressurised systems. So, let’s have a look at this system here. So here’s the loft that we’re looking at and the particular part we’re going be taking notice of is that bit there. So here we are on the lines down of possibly, possibly the worst pressurised heating system install I’ve ever seen. Right, so, we’ve got our feed from the cold main here. That’s this valve here, we’ve got our braided hose here, that’s also got a little valve in it that you can’t see, but it’s just a little black-handled valve. Let’s get round here and have a little look. Can you see that? There it is. Now that braided hose comes up here and through this, which is a non-return valve, That means the heating water can’t push back down the mains if there’s any problems like that. Next, we have our little manifold, All this is, is just a series of ports that allow water in and out of this particular part of the system. Now, we’ve got our pressure gauge here, which is currently reading about half a bar, which is borderline . This system’s colder than mine, so when it heats up, I imagine it’ll come up to about one to one and a half bar. At the top, we’ve got our high-pressure relief valve.

Now this has a small spring in it, so if the pressure gets above . bar, which is all the way around here on there, that spring’s going lift up, and it’s going let water out of this pipe here, and that’ll go outside, where it’s terminated at a safe place. The next thing we have to look at is this part here. This is the expansion vessel. Water can expand down into this and be happy. And this side here is heating system pipe. Make sure they’re both off. They should not be left on. Ever. Alright? “But now,” I hear you say, “What about draining the system out?” Well, most heating systems– , let’s say we’ve got a two-bed house, ? Look at this. A little– well, a two-floored house, right? We got a radiator down here, radiator down here, radiator down here, and a radiator down here. Say the boiler’s in an outhouse or something like that. Usually, what we’ve got here, we’ll have an airing cupboard up there. Your boiler flow will go up into the airing cupboard. And then, it will get distributed around these rads. Off through each radiator, it’ll come down like that, oh, lovely, and they’ll join up at the bottom and then go back to the boiler. Now what you do is, you’ll be looking for is, you go downstairs, and you try and find a little drain-off where you can put your hose outside and let water gush all over next door’s primroses, or something like that. Now, that’s great, you know. Sometimes, that’s brilliant.

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