Air bubbling in closed central heating system - help please

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Hi there,

The highest radiator in my CH system has recently started to make a loud bubbling sound when the CH system turns on. It sounds like a number of large air bubbles are passing up to the top of the radiator in question. I believe the rad is the highest one in the system.

I have bled the radiators on 2 separate occasions one week apart. A seemingly large volume of air was released from the radiator in question but none was found in any of the other rads. The water in the bled radiator was only slightly discoloured and the water from all of the other rads was clear. The first time I bled the rads, the boiler pressure dropped almost half a bar from 1.5 bar and I topped it back up. I did not do this the second time I bled the rads and the boiler pressure is now 1 bar.

This problem has occurred since I recently turned on the CH in response to the colder weather. The boiler then had to have its expansion vessel repressurised as it had absolutely no pressure in it resulting in the boiler pressure rising and water discharging through the PRV and pipe to the outside. The boiler pressure was set at 1.5 bar after the expansion vessel was repressurised. At that time the system was partially drained and 1 litre of Sentinel inhibitor added as a test showed a low level of inhibiter was present.

My central heating system is 3 years old and comprises the following:

- Worcester Bosch Greenstar 24i gas condensing boiler.
- Megaflo 250HE unvented hot water cylinder.
- 11 radiators over 2 floors with 1 towel rail fed directly off the bathroom radiator and a Smith’s plinth level heater in the kitchen also plumbed into the system.
- TRV fitted to all of the radiators except the bathroom rad and the rad in the room where the room stat located.
-Copper piping throughout the CH system.

Does this mean I am more likely to have a water leak in the CH system or is air being drawn into the system or is corrosion generating gas in the system? The boiler and unvented cylinder are to be serviced next month, what else needs to be done to sort the air problem out?

Many thanks for your helpful replies.

Mutley56
 
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As an update to this recent post, I bled the radiator in question again yesterday and the boiler pressure dropped by about 0.25 bar.

I would appreciate anyone suggesting what the next step is to find the source of the problem. I am going to bring forward the boiler service and ask the engineer to look at the problem but I wanted to have an idea of the liekly cause(s) beforehand.

Many thanks.

Mutley56
 
Sounds like you've just got a load of air in the system from the dain down.
Try running it with all the rads turned off except one & cylinder circ's turned off as well, that should push the air to the one rad.
You might have to do this to all the rads in turn.
Might also be worth checking the auto air vent on the boiler is open as well.
 
Thanks Keego for your advice. I'm hoping its only a volume of aid still rapped inside the pipework and not anything else like leaking pipes / joints or expensive components inside the boiler itself.

Thanks again.

Mutley56
 
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Update:

When I bled the radiator yesterday onto some kitchen paper, the water was slightly discoloured and had some deposits in it. I kept the paper and looked it today. There are tiny sliver flecks of material on the dried but slightly stained kitchen paper. What are these metalic flakes and where could they have come from within the sealed central heating system?

Thank for your opinions.

Mutley56
 
I think that you are being over sensitive.

Run it at about 1.0 bar cold for a week or two and check that pressure is maintained if you dont bleed anything.

Your system is pressurised. That can cause water to leak out but not air to enter it.

The only gas can be as a result of corrosion which is highly unlikely now you have inhibitor added.

Tony
 
Thanks for replying Agile,

How do I run it cold; do you mean the leave the radiator cold by setting the TRV on the radiator to the lowest setting ie. Frost?

Thanks.

Mutley56
 

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