Hi,
How much time would one normally expect (in a sealed system) before all the air is out?
I had a new CH system fitted over two weeks ago and I am still having to bleed some of the radiators every couple of days. The pressure is not dropping noticably so I don't think there is a leak anywhere!
I always bleed the rads when the CH is off (Does this still apply in a sealed system?).
TIA, Mark
Each time you bleed, I assume you are topping up again through the filling loop?
Each time you top up you introduce more airated water to the system.
What you should notice is that each time you bleed it takes slightly less time to let the air out.
I'd say you should be getting very close to it now.
Most of it should be out in a few days. You might still hear the odd bubble going around the system for a few weeks. I last topped mine up about 2 years ago, and I still occasionally hear a bubble force its way through one of the flow restrictors.
Is this because they are getting cold at the top, or just because you can still get some air out?
Leaks are two-way affairs. Often air will leak in faster than water leaks out, even though the system is pressurised. You might not see water leaking out as it can evaporate as fast as it leaks when system is warm. Leaks are often more 'visible' when system is cold.
If you are removing air from the system and it isn't being replaced, I would expect the pressure to drop due to the bleeding alone. Do you know if an inhibitor was added?
When the system is cooled down, much of the air can redissolve in the water. I would speculate the best way to bleed it is to crank it up to maximum water temperature (when the maximum amount of air will come out of solution) and then bleed this before it cools and redissolves. I never heard anyone say to only bleed when CH is off.
No. As the pressure has not dropped I did not bother. Maybe this is wrong but I'm no expert at this.
I've not really noticed the time taken to bleed the radiators.
Mark
Both.
Are you saying that I may have a leak? If so how can it be found since most of the pipes are under the floor?
I don't think any inhibitor was added. I'll have to speak to the plumber (if I can find him:-)
I was told this by an experienced BG heating engineer. It certainly made a difference on my old gravity system.
Mark
FWIW. We have a sealed system and I bleed our radiators once a year. I get them up to temperature, switch the heating off, then bleed the air out. Since that lowers the pressure I then wait for the system to cool down and top up to the working cold pressure (1 bar in our case). It might be a bit of messing around but it's only once a year (we have a loft conversion with a radiator - it collects all the air so I suppose we have it easier than normal).
Also FWIW! In my pressurized system with attic rad it is (both) towel rads that collect the air - one more (nearest the boiler) than the other. The ****** plumber who installed the system did not add an inhibitor. When I asked him during commissioning if he was going to he said that he didn't bother! Oh my simple minded trust ;-( I have flushed it twice and added a tube of Fernox (last June) and I'm still bleeding the *****ing system. I've just ordered some DENC valves to make my life easier!
Richard
In article , Mark writes
If it was added, the water from the radiators should be straw coloured, drain a little from a bleed valve to check. If clear, find plumber and threaten with violence . . .
The water in my Fernox treated system appears to be colourless - if the colour of the water that emerges when bleeding the rads is anything to go by - but it does taste horrible tho'!
Richard
Bugger, maybe my straw colour was the beginning of rust, tell me there is a hint of straw colour in yours, please . . . .
I'm going a bit by the colour of the liquid Fernox I added when I commissioned the system and the colour of the water when I bled the it. 2 years on and a couple of partial drains later and the colour is getting a bit darker, so maybe a drain & refresh of fernox is called for.
Then something must be wrong.
Why do you say that? Every now and then a sealed system needs topping up. That introduces cold water which contains air. It is therefore reasonable, I think, to expect to have to remove that air once in a while.
If you think there is a specific problem I would like to know more about what you think it is. Perhaps a very slow leak somewhere?
But it should be a very small amount?
By your description, it's a *lot* of air.
That was my thinking. I suppose it could be multiple weeps that are so small they don't show but just evaporate.
No it's not much air at all (nothing like the amount the OP is bleeding) and it's only from the one radiator in the loft. Just the top few cm (10 tops) is cold once a year on a single radiator about 120 cm long (normally in autumn when the heating goes back on). In two years I have only had to top up the system 3 times. I am interested to know where the water goes though.
I have lifted floorboards all over the house for another job and so I have seen almost all the plumbing and none of it showed signs of a leak.
ISTR mention of testing the strength of inhibitors? Don't know how tho'.
Richard
I do, it was my post ;-)
It's a greyish colour.
I'm still having to bleed quite a bit of air out of one or more radiators.
Mark.
That doesn't sound too good, the corrosion product of iron (steel radiators) in heating systems is black so grey suggests that the process has already started. This suggest that an inhibitor has not been added. It's difficult to tell without seeing it but you could do a quick test on the fluid as follows:
Draw off a small amount from a radiator, just 50ml or so, then dilute it 4:1 with clean water to make about a cup full (200ml) drop in a clean steel nail & leave for 24hrs. If there is any trace of rust on the nail then drain, flush (with just water) & refill with correct level of inhibitor.
The test is a close copy of an earlier post of mine. If the nail has any hint of rust then kick arse on the installer. Polite approach probably the best, asking if he added an inhibitor (giving him the chance to say he forgot). If answer is no then quote the British Standard for domestic central heating systems to him stating that a chemical flush followed by clean water flush (hot & cold) followed by filling with water and inhibitor is required, it's BS
5449. I haven't read it but I bet it will say something like that :-).There are other possibilities but perhaps post back again with the results of your test, maybe best in a new thread as this one has sunk down the group so much that I only caught your post by chance.
HTH
With a sealed system you're right. With an incorrectly installed vented system it is possible let air in when you open a bleed point. Hence the advice.
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