Air circulating in rads

25 Jan 2006
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United Kingdom
Hi All..

Glow Worm Xtrafast 96 combi....

Recently did a complete mains water flush on my system.......worked a treat as loads of sludge and black bits came out.
Refilled the system (not adding and inhibitor at this point as I wanted to ensure the system was running OK, but have the x100 ready to put in.)

System ran very well for a week (best it has EVER been).
Now I have a couple of other odd things that are occuring.
Firstly I can hear bubbling noise going through the rads......this happens intermittantly whilst the system is running.
Secondly, when I then turn the DHW on for a minute or so, then turn it off......and when the boiler fires up again (a minute or so later) I hear a 'whooshing' in the boiler for a few seconds and more air bubbles can then be heard at the rads a 10-15 seconds later.

questions are:

Will adding the x100 fix these issues?
Is there a hardware fault somewhere? 3 Way valve?
Is there any settings on the boiler itself that is adjusted would fix the problem?

Thanks very much in advance for any help.
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Adding x100 will not cure.
Open the auto air vent on the boiler

Hi Steve..

First of all thanks.....
Is that the valve on top of the waterpump? If so, it doesn't actually have a cap on it right now! Air did come out of it when I refilled it recently so know it's working OK.

Although I'm most concerned about air getting into the system rather than out of it! If I can fix the 1st bit then I don't have to worry about getting it out again!
Once again, many thanks.
Start with the basics.
Make sure the automatic air vent on top of the pump is open and working.

If your system has pipe drops to individual downstairs radiators run each one of those rads on there own for a few minutes by turning every other rad off.
Does your system have any high spots on the pipework which require venting?
Vent all the radiators again.
It is good practace when a system has been empied/flushed to vent all the system again after a few days.
Is your boiler fitted where the cylinder was originally? If not there could well be dead legs either in the old cylinder cupboard or just under the floor. There may well be air bleeds stuck up in the cylinder cupboard on your old pipework. eg. domestic return/hot water. Was your old cylinder in the loft? There could be air vents up there that want venting?

Any way you look at it if you are hearing bubbling noises in the system it is an indication of air in the system.

Hope something here helps.
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Yep, valve on top of pump seems to be letting air out fine.

But most of the air seems to be 'appearing' when the DHW is used and and then the CH circuit kicks back in. I.e. when the 3 way vlave returns iself to it CH setting, lots of whooshing is heard and the temp gauge surges up to 75 (normal op temp is set at 64).......then the air can be heard a few seconds later coming through th rads.
did you close the bypass when flushing if so make sure it is open and adjusted correctly

Yes, closed bypass (on pipe work NOT the one on top of the 3 way valve) when flushing, and reopened to original setting (it's just the screw type not an auto-bypass).
How should it actually be set as I have tinkered a bit to see if that eliminates the problem, but no luck so far.
Is the system pressure when cold between 1-2 bar?
What is the system pressure on yours when cold?
what is the pressure showing when fully up to temperature?
If the pressure is excessive when fully hot you may have overfilled the system or there is a chance the pressure vessel needs attention.
How many radiators are on your system?
Did you do all the checks i posted previously?
The XTRAFAST boiler has a built-in bypass. This must be
adjusted according to the requirements of the system, refer to
the flow rate pressure curve (diagram 4). The boiler is supplied
with the built-in bypass open a half a turn. It is adjusted by
turning the bypass screw (a), see diagram 15.1. Turn the screw
clockwise to close the bypass. When using thermostatic
radiator valves (TRV’s) on all of the radiators, it is essential that
a separate, adjustable bypass of 15 mm minimum diameter is
fitted between the flow and return of the heating circuit, see
diagram 8.2. Any bypass must be fitted before system controls.

Open the bypass fully to see if this clears the problem, if it does close it bit by bit until the problem returns then open it half a turn.
Thanks again Brian..

Sorry for delay in responding.
I will check the steps you kindly posted for me.
Some of your pints do not apply (I.e. old pipework, high pipework requiring venting), but many thanks for even considering them for me.

Will get back with results......or dare I say it......a FIX!
This sounds almost exactly like the problem I have with my new boiler! :)

Unfortunately no solutions offered at the moment, but I get 'air bubbles' when the DHW is first switched on after a night:

I have since drained my system and filled with a cleaner which is currently going around the system and this has got rid of 70% of my air bubbles.

Don't forget that as you are not running with inhibitor in your system, corrosion will be taking place which produces hydrogen - which you could mistake for air.
Did you find a solution to this yet?
Not yet, still working through solutions/checks.

Here's the latest.....
I have 13 radiators (all have recently been removed, taken outside and flushed with mains pressure)
Auto air vent on top of pump AOK
Expansion vessel - OK and charged with 15psi
Pipe Bypass valve set @ 45 degrees (previous setting)
Rads have been vented once more
System pressure (cold) is 1.4 bar
System pressure (hot) is 1.6 bar
x100 now in system after final flush (flushed water now completely clear)

Now about to start tinkering with Bypass valve that resides on the 3 way valve on boiler.

Will post again over the weekend.

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