We've never had a pressurised CH system but eldest has recently bought a house with one and I'm 'learning' about them ;-)
How often do you need to re-pressurise a system? Is it normally something the home owner would do, a bit like bleeding the rads?
(I appreciate that, if you bleed the rads on such a system, you will need to repressurise it.)
Depends how much it's leaking :-P
Andy Burns wrote in news:g3rpruFfaqvU1 @mid.individual.net:
Or how much gas is liberated from the water.
I'm assuming it has inhibitor which tends to reduce the 'release' of gas.
I was hoping for a typical answer in a system with no real leaks- although even a sealed system will leak a bit.
For example, with a conventional system (ie unpressurised), I'd say, even with no leaks, inhibitor, etc, bleeding once a year would be normal. Probably not air in all rads, but a bit in a few.
Would that be typical for a pressurised system, or would more often be required?
Andy Burns formulated the question :
..and they all do leak to some extent..
In the case of our system I would say after more than 6 months. If the pressure drops our boiler won't run, so one thing to check is the system pressure. There is a gauge and the needle would be in the red. On our boiler I just have to turn one valve and watch the pressure rise to the point where the needle is well in the green, but not at the top.
I would suggest that you make sure that your eldest can deal with the problem. :-)
If the system has recently been drained and re-filled then it takes a while for the air to come out so topping-up every few days might be prudent, but thereafter it's once in a blue moon unless there's a leak. If the pressure gets too low (0.5 Bar IME) the boiler locks-out until the pressure is re-established.
Sealed systems have a number of advantages and, AFAIK, no disadvantages.
One thing that you may not be aware of: there will be a pressure (expansion) vessel to allow the water volume to increase/decrease with temperature. The expansion vessel contains a rubber diaphragm, the dry side of which is pressurised with air - there's a valve like those on a car tyre. If the diaphragm fails (as happened to me) you can keep the system going temporarily by letting air into a radiator.
If no obvious leaks, perhaps once a year to never.
I have a tiny drip on the hall rad (that gets fixed next week as we're draining down to fit the UFH). I have given it about small 3 recharges in the year because of that.
Mine took a hell of a lot of bleeding - lasted about a month. That's partly because I have a tortuous pipe route upstairs with 3 full up/downs to get to some rads. It's unavoidable.
Most of that was trapped bubbles of air arriving at the bathroom towel rail which seemed to be the place where it all gathered.
Some must have been dissolved air coming out too.
I would not expect much of any hydrogen due to the inhibitor. It should settle down in a week or 3 and not produce any gas really.
In an ideal world, never. However if you bleed rads, or have any tiny leaks then you may need to from time to time. It should not be mor than a couple of times a year though.
Yup, there is normally a "filling loop" (i.e. a connection between cold main and heating circuit - made via a couple of taps and a non return valve). You just open the taps and top up until you see adequate pressure on the gauge. Note some combi boilers have the filling loop built in, then there is usually a key of some kind to turn to add water.
Kind of...
Probably yup. The "slack" in the system is taken up by an expansion vessel - so a bit of bleeding will not necessarily require topping up.
Chapter and verse of sealed systems here:
They can do the repressuring etc, the boiler they have has gubbins that make it easy, that isn't the question.
What I wanted to advise then was typically how often it may be required. Partly so the do it and partly so they know if there is an issue.
Your 6 mths is in the same ball park as others. So I think twice a year is a good guide. More often, suspect a leak. Less, don't worry ;-)
In a vented system the primary water is constantly exposed to air in the header tank, so it can absorb more air. The is also the danger than it can pump over or draw air in directly via the F & E pipes. Lastly you can get gas produced as a result of corrosion - again more likely on a vented system because of the constant availability of fresh O2
If filled from scratch, you will probably have to bleed and top up several times in the first few weeks - it takes a while for all the entrained air to come out of suspension. Once its working normally, I would not expect to touch it more than once or twice a year - perhaps a bit more at the start of a season if the rad circuit has been off for a while.
Note that leaks can be too small to see - a weep that leaks water so slowly it evaporates before you get a chance to see it "wet".
I had one recently at the base of a push fit fitting. The clue was slight hint of verdigris staining on the paint on the pipe of a rad tail[1]. Resting a bit of bog paper against it for a few days showed a green patch forming on the paper. Not enough leak to see, but enough to require a top up of about a litre every couple of weeks.
[1] In fact it was this one:When doing bathrooms earlier in the year, I also took the chance to swap a rad in the downstairs loo. However since I was only partly drained down (i.e. just the upstairs pipework) I used a pushfit for the final connection so I could work "live". Alas that cuprofit must have been knocking about in my plumbing bag for too many years, and did not make a perfect seal it transpired (although it did take a few months before it started to leak)
Don't they stop working if the pressure drops, either from leaks or failure of the pressure vessel?
Probably preferable to a vented system leaking indefinitely into the fabric of the house. At least with a sealed system you are alerted to the fact that there is a fault, and the maximum amount of water that can leak is limited.
yes, that's what I said in the text you deleted .... but it's an advantage because it alerts you to a problem and prevents the heat exchanger from being fried
It seems to be quite often the case that there are one or two rads in particular that cop most of the air in many system. (you can usually predict which it will be - its the most awkward to get at and bleed!)
In my case its a small rad at the back of the upstairs airing cupboard that I can only reach by laying on the floor and trying to slide under and past lots of slatted shelving and piles of laundry etc.
I'm about to add 6 autobleeders (2 for conservatory UFH), 4 for the main heating rails, south and north dormers - the highest bits of pipe in the system.
Should make the refill much easier.
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