CENTRAL HEATING. How to reduce the pressure in your Combi Boiler. How to take some pressure out of your combi boiler. Central Heating. High Pressure. Expansion vessel. combi boiler. So if you have a look at your pressure gauge and there’s too much pressure in your boiler, we’re going to take a look at that, show you how to reduce the pressure in the boiler, and also just go through some of the causes of why you may have too much pressure.

So first of all, we’ll look at the filling loop underneath the boiler and we’ll see if that’s been left open. So let’s have a look at that now. When we look at this, we can see this side is open, so that means this here, that should be closed like that, if you can see. And then that one that there is closed as well. If they were both open then they’d be like that and then your pressure gauge would continually just go up all the time.

So after you have filled the boiler, normally we would only fill it to about one when the boiler is turned off and the boiler is cold. So if you’ve done it to one, always make sure you turn these back off.

I’m now going to go through a few different ways of how you can reduce the pressure, and then I’m going to go through, if it happens again, then what ever problems you may have.

So on this wall we’ve got filter just underneath the boiler and by just undoing the filter under here, this will take the water out of the system, or take some of the water out of the system, and that will lower the pressure, so I’ll show you that now.

So you can see this pressure gauge is up there at two and a half, and then if we just open this here, and we start to let some water come out, we can see the pressure gauge, we can see the pressure gauge goes back down. If you’ve taken a lot of water out like that, and that pressure gauge is still stuck up there, then it may be you’ve got a faulty pressure gauge. So what I’ll do now is I’ll just tuck this back up a little bit and then what we’ll do, I’ll show you some other ways if you haven’t got a filter that you can do. So again, I’m just going to overpressurize it, and then now what we’ll do is we’ll go to a radiator.

Doing it from a radiator can take quite a lot longer, but what you do is just bleed it, get a jug or something to put under there and then just drain into your jug. You might need a cloth underneath as well because it’ll probably drip. And just be careful not to undo it too much with this key. If you undo the out too much, sometimes that can actually shoot out and then you’ll be in the right mess then. Doing it this way might take quite a while because you’re only taking a right little bit of water out at a time. So what you’ll have to do is do this and then close it, and then go back to your boiler and check. You can always put more pressure back in if you need to, so we’re going to a look at the boiler again now. When we look at the boiler, the pressure’s gone down a little bit, but as you can see if you’re going to do it from a radiator, that’s going to take quite a while.

You could also undo one of the nuts underneath, if you’ve got somewhere where you could undo one of the nuts and you could let some of the water come out a bit. But obviously you have to be really careful with that. Also, it may be that you’ve got a drain off valve somewhere on your system and if you have, you could just put a jug underneath and then just undo your drain off part of it. Obviously that would be on your system like that. So that’s another way that you can take the pressure out of the system.

If you’ve managed to get your pressure back down to one, then what you need to do now is when the system’s cold, you want the pressure to be at one bar. Just round about one bar. And then when you heat the system up, so you’ve checked all valves and everything’s turned off underneath, except one bar, system’s cold, and then you put your heating on and this pressure gauge, it’ll start to go up, but you only want it to go up a little bit. If it starts going back up to over two or a three bar again, then that would indicate you’ve got a problem with the expansion vessel inside the boiler. And it may be that it needs servicing, it just needs the expansion vessel pumping up. It may be that you need a new expansion vessel, but more than likely it’ll just need pumping up.

It could also be that the expansion vessel is undersized for the size of system that you’ve got. So if you’ve got a really large house, then expansion vessels in boilers are only normally seven, eight, nine litres. So they’re not really designed for big massive houses. So it could be that you need an additional expansion vessel.

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