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How to repressurise a combi boiler. Vaillant / Glow Worm F22 fault
Low pressure on Valliant boiler, Glow-worm boiler, your Ultracoms, Flexicoms. What else is there?

EcoTec Pro.

EcoTec Pro. I’m going to show you how to top the pressure up. Today I’m going to show you how to top the pressure up on your Valliant and Glow-worm boiler. So underneath the boiler, you’ve got two taps and they’re both closed when they’re in this position. To open it you turn it quarter of a turn like that. And then the other one you turn slowly and you’ll hear it fill. As it fills, the pressure gauge will rise. And you want to tack that to approximately 1.1, 1.2, 1.3 bar, as it is now, and then close it back off again. And then close the other one off as well. There you go.

So just to explain what’s happening here. This is the pipe on the right-hand side underneath the boiler and this tap is now closed. And when you open this pipe, it’s allowing cold water to go around the flexi-pipe at the back. So if you see that silver flexi-pipe at the back, so now you’ve got your cold water from your cold water mains and it’s going round that pipe at the back, and then it’s going over towards this tap here. And this tap is now closed, but when you open it, you’re allowing the pressure to go into the central heating part of the system. And then what that will do, it will put the pressure up on the system.

Sorry about the poor quality in there. It were quite awkward to show you. But what you’re trying to do, and this is the same for almost all combi-boilers… and always read the installation instructions if you’ve got them available. But normally you’re wanting to top the pressure up to around one bar or just over one bar, maybe 1.1, 1.2, depending on the boiler. Some of the ATAG boilers, they need to be about 1.4, but as I say, you’d need to read the installation instructions for them. But what you’re trying to do, you’re trying to get your… so inside the boiler, the boiler it has a pressure sensor and that’s to protect the boiler. Some boilers don’t have them, so for instance, your Worcester’s, they don’t have a pressure sensor and your Viessmann boilers, they don’t have a pressure sensor either. And there’s probably other boilers as well, but most combi-boilers have a pressure sensor. And what that does, that’s to protect the boiler.

And what you’re trying to do is, if say, for instance, you might have a little bit of a weep on a TRV topper, it might have leaked a little bit of water out, or you might have bled a radiator. And as you’ve bled the radiator, it’s allowed the pressure to go down. Or it might just be just normal evaporation in the system because the boilers have built-in auto air-vent. So it could be that it could just be that, naturally. Normally, it’s nothing to worry about. If you had to do it every day, then obviously you might have an issue and you’re going to be… it’s going to be better if you got a plumber or somebody to come out and have a look at the system to make sure it’s all okay for you.

But generally what you’re trying to do, you’ve got your cold water main’s, so your mains pressure. You’re opening the taps underneath, and you’re getting the pressure from your mains through the boiler and into the central heating system. And that puts the pressure up. You’ve got to be really, really careful you don’t put too much pressure in because if you put too much pressure in and I’ve done a video on too much pressure and how to get the pressure back out again. So if you have put too much pressure in, then it might be worthwhile having a look and searching for that video as well. It shows you how to take the pressure back down. But one thing as well just maybe to point out in this video is, if your pressure is… if it’s going down a lot and you’re topping it up to one and it works, and then you go and next day it’s gone down again. Then it could be… there’s a few things it could be.

It could be that the boiler need servicing. And it could be that the expansion vessel inside the boiler has lost its charge. And that’s something to check and also the PRV. So it could be dripping outside on the PRV. So again, that’s something to check, but usually, this is a time then when you really need to be looking at getting your boiler serviced. Somebody that’s going to come along, strip it down, drain the boiler down, take the water out of the boiler and repressurize the expansion vessel. Do a good job for you and maintain the boiler. So what a lot of people do is they’ll buy a new boiler and then some people get them serviced and get them looked after. But some people don’t bother. I mean, you wouldn’t go buy an £100,000 Mercedes and then put old engine oil in it.

Allen Hart

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