Automatic Need to Bleed Air from System some time after refilling?

CBYR1983

I read or heard from somewhere that once a system is drained and refilled with fresh water, after a while air is created by the constant heating and cooling of the water, requiring the rads to be bled.

Is this nonsense though? I can't see how this could happen without some water leaving the system (e.g. through a leak), or water turning to vapour (e.g. boiling)?

I would have thought that the system would only need to be properly bled once refilled, and any air showing in the system thereafter is through leakage, rather than any natural occurrence.


Would be good to get a view, because I'm finding that I have to bleed (just twice now on one upstairs rad) a system that was drained and refilled in June.

heinbloed

Is this nonsense though?

Absolutly not.
Ask your
plumber why he didn't install automatic air valves.

DoneDL

There are occasions when some air might be in the system after refilling but not once a system settles, normally after a day or two. Is the system sealed or open, was inhibitor put into the system. Once a system has been running for a while it should not require constant venting or bleeding.

CBYR1983

It's an open system.

Anyone got any further insight into why this happens and what to do.

How would it be avoided with "automatic valves"?

roy rodgers

If its an open system you must have a soild flue boiler attached to the heating?? and I say air is been pulled into the system via expansion pipe or the system is pittching into the expansion tank and is then bring air into the system. Which is not good for your rads. To slove this you would have to change the position of the pump or the cold feed.
Have a look in the attic when the boiler or (boilers) are running and see can you see water flowing into the expansion tank (small tank) from the expansion pipe...

Sparkpea

I advise this is done myself, so I don't believe its nonsense but I didnt know its to do with the heating/cooling of the fresh water. I would tell clients to bleed their system 3-5 days after i've refilled and bled it myself as sometimes the system needs to balance itself out and there still may be air in the pipework

ntpm

roy rodgers wrote: »

If its an open system you must have a soild flue boiler attached to the heating?? and I say air is been pulled into the system via expansion pipe or the system is pittching into the expansion tank and is then bring air into the system. Which is not good for your rads. To slove this you would have to change the position of the pump or the cold feed.
Have a look in the attic when the boiler or (boilers) are running and see can you see water flowing into the expansion tank (small tank) from the expansion pipe...

Totally agree.
Problems could be getting worse as intake of air (oxygen rich) will cause corrosion and sludging in radiators, which in turn causes more gaseous vapours.... sometimes this air will be vented by the automatic air vents (AAVs) depending on their locations.
However this should not be relied upon to eliviate the problem. Find the cause and rectify fault.
Inhibitor will reduce the corrosive reation in normal operating circumstances but not in an incorrectly designed system.

Also to add when draining down a system and refilling you will introduce air.
The system is run to allow the air to move round and any air trapped in pipework will be moved round and usually end up being vented through the AAV's at boiler, cylinder and any high places.
Also manual venting the radiators in system will remove the air.
Note: the Open Safety Vent pipe (also incorrectly know as expansion pipe in heating systems) may vent air on initial filling/venting procedure but should not do this afterwards. If it does it highlights an issue in the system design/ operation (as roy rodgers describes)
You may need to vent radiators again a few days later for any air still stuck in the system but not on a regular basis.

CBYR1983

roy rodgers wrote: »

If its an open system you must have a soild flue boiler attached to the heating?? and I say air is been pulled into the system via expansion pipe or the system is pittching into the expansion tank and is then bring air into the system. Which is not good for your rads. To slove this you would have to change the position of the pump or the cold feed.
Have a look in the attic when the boiler or (boilers) are running and see can you see water flowing into the expansion tank (small tank) from the expansion pipe...

All I have is big old oil boiler. However, I think it may also have been capable of taking solid fuel.

At one stage there was also probably a back boiler but the fireplace was removed.

The system is generally ok, but I do get gurgling in a particular rad downstairs, which is close to the boiler. I also find that the rads upstairs do not always heat fully at the bottom. I think this is through poor balancing which could be causing sludge to collect in the rads which are furthest from the boiler or simply not giving them their fair share of water.

I've never noticed any water being forced into the expansion tank in the attic.

As I was saying before I think there may be a chemical reason for this, I think they say that water which is reheated over and over has a different composition to cold water.

roy rodgers

CBYR1983 wrote: »

All I have is big old oil boiler. However, I think it may also have been capable of taking solid fuel.

At one stage there was also probably a back boiler but the fireplace was removed.

The system is generally ok, but I do get gurgling in a particular rad downstairs, which is close to the boiler. I also find that the rads upstairs do not always heat fully at the bottom. I think this is through poor balancing which could be causing sludge to collect in the rads which are furthest from the boiler or simply not giving them their fair share of water.

I've never noticed any water being forced into the expansion tank in the attic.

As I was saying before I think there may be a chemical reason for this, I think they say that water which is reheated over and over has a different composition to cold water.

When fresh water is heated up it will create air bubbles. just looking a kettle while its heating up the water and you will see the bubbles forming.
So the same thing is with a heating system after it has been re-filled but with a heating system the air gets "boiled out" after a few days and no more air is present in the system if the system is air tight, no leaks, no pitchting, or that the pump is not sucking air into the system via vent pipe or through automatic air vents.
Air can be sucked through many things like plastic piping, fittings, valves.
Its got to do with the circulating pump been on the negitive side of the hesting system..

To me air is getting into your system either by a leak or by a negitive draw. The radiators been cold at the bottom is a prime indication that air is present, its breaking down the rads and now "sludge" is lying at the bottom of the rads.

heinbloed

Get the system balanced as a first step, this would show if the radiators are filled with sludge or not.
Diffusion of gas/oxigene into the 'closed' heating system happens all the time. A natural law, therefore airvalves are a 'must-have'. Every radiator has to be bled at least once per year.
Automatic airvalves will do this automatically, all air pentrating the system wil be caught at the highest spots and squeezed out by the present pressure.
A set of half a dozen (for radiators) can be bought cheaply at the DIY market and be self installed.
About the diffusion:
Air gets through pipes and fittings, through sealants and membranes. This is normal and simply can't be avoided. A law of physics. Only the rate of diffusion can be influenced, not the fact that it does happen.
A particular spot where air penetrates the closed circuit in the typical home heating system is the expansion barrel. Here a membrane of EPDM (synthetic rubber) holds pressurised air on the one side and the water on the other side. EPDM is by far not diffusion proofe, it lets air pass through it. Therefore the pressure check of the expansion barrel is routine work when doing the anual check, it usually needs to be topped up.
But diffusion happens also at ALL other parts of the heating system, at all times as said already.
So instead of ignoring this fact one should learn to live with it. It makes life easier.
A plumber who does not install airvalves in a pressurised central heating system is not working correctly but against the rules.