Gurgling and air in central heating

[Deleted member 123817]

The boiler won' be very happy if the flow & return are swapped over however unlikely that it was installed this way. Just feel the hotter of the two pipes and check in your users manual if correct.

 

[jim843]

When the system is cold top up to about 1.5 bar and see if that has an affect. I wouldn't go as high as 2 bar as this is likely to cause the prv to discharge when the system is hot, the vessel condition and charge will have an affect on system pressure as well.
Why would air settle in the towel rails and not on the floor above? Air is less dense than water so you are correct to assume that it would settle at highest point of the system and usually does, however by design towel rails are taller and it's possible the air is getting stuck at the top and the water is circulating below it, happy to be proved wrong there though?

I jumped the gun a bit and pressurised to 2.2. So far no air in the bathroom rad.

I’ll check the flow and return when I have a sec.

So far the upstairs rads seem much hotter (a good thing).

 

[jim843]

When the system is cold top up to about 1.5 bar and see if that has an affect. I wouldn't go as high as 2 bar as this is likely to cause the prv to discharge when the system is hot, the vessel condition and charge will have an affect on system pressure as well.
Why would air settle in the towel rails and not on the floor above? Air is less dense than water so you are correct to assume that it would settle at highest point of the system and usually does, however by design towel rails are taller and it's possible the air is getting stuck at the top and the water is circulating below it, happy to be proved wrong there though?

Boiler was at 1.5 when cooling. I pressurised to 2.2 (based on your advice of .5 and a bit).

The bathroom towel rail seems much hotter, which is good.

There is still a tiny bit of air in the bathroom towel rail every day. I want to say quite a bit less but there’s nothing scientific about it. I turn the bleed valve and I get a bit of air for half a second/second.

Other rads in the house, when bled, are just instant water.

Still need to check if flow and return on boiler have been flipped accidentally.

Any ideas?

 

[jim843]

When the system is cold top up to about 1.5 bar and see if that has an affect. I wouldn't go as high as 2 bar as this is likely to cause the prv to discharge when the system is hot, the vessel condition and charge will have an affect on system pressure as well.
Why would air settle in the towel rails and not on the floor above? Air is less dense than water so you are correct to assume that it would settle at highest point of the system and usually does, however by design towel rails are taller and it's possible the air is getting stuck at the top and the water is circulating below it, happy to be proved wrong there though?

@SJB060685 checked system at about 9am this morning and there was a 1sec burst of air. Checked at 10:15am and there was another 1sec burst of air.

So air somehow being pulled/generated in the system?

 

[SJB060685]

@SJB060685 checked system at about 9am this morning and there was a 1sec burst of air. Checked at 10:15am and there was another 1sec burst of air.

So air somehow being pulled/generated in the system?

Would appear so yes mate. Are you sure it's just air and not hydrogen?

 

[jim843]

Would appear so yes mate. Are you sure it's just air and not hydrogen?

I’m not sure.

Is this the old lighter trick? Not quite sure how best to test it out.

 

[jim843]

Would appear so yes mate. Are you sure it's just air and not hydrogen?

@SJB060685 just reading How to | Circulation Issue Causes Central Heating | Sentinel - https://www.sentinelprotects.com/uk/support/how-diagnose-circulation-issues

• If there is a reddish tinge to the water, it indicates that iron oxide is present, suggesting active corrosion. The system may be drawing in air.
• If there are black particles present in the water, these are most likely to be magnetite. As this is the final stage of corrosion, large deposits can be expected within the system.

I'd say I've seen both of these in the system.

I bled the rads last week and the water was reddish in places.

I also bled the towel rail on the automatic air vent side (you have to unscrew the whole thing). The pressure was high and a jet of black water shot out of the rad.

Could it be as simple as the system needs a thorough clean?

 

[SJB060685]

That is an indication you have sludge (magnetite) in the system. This is caused where you have large amounts of air entering the system and it and the water reacts with the iron content on the steel radiators causing corrosion. Hydrogen may be produced as a byproduct of this corrosion as well. The lighter or match trick would reveal if hydrogen yes. Next time you vent a radiator vent a small sample of the gas into an upturned cup and offer a flame to it, if it pops it's hydrogen. Don't vent too much into the cup though.

 

[jim843]

That is an indication you have sludge (magnetite) in the system. This is caused where you have large amounts of air entering the system and it and the water reacts with the iron content on the steel radiators causing corrosion. Hydrogen may be produced as a byproduct of this corrosion as well. The lighter or match trick would reveal if hydrogen yes. Next time you vent a radiator vent a small sample of the gas into an upturned cup and offer a flame to it, if it pops it's hydrogen. Don't vent too much into the cup though.

Thanks @SJB060685! I'll give it a few days and vent into a cup so there's a bit more air/hydrogen.

All radiators in the property are less than 5 years old. Most are column rads.

Does the air/hydrogen in the system mean that air is entering the system now?

Or can the air/hyrdrogen be a consequence of a prior leak and subsequent corrosion?

 

[SJB060685]

Hydrogen build-up is a by product of the rads corroding, I believe it can form from galvanic corrosion as well, however I can't find anything to stare that for sure. Hydrogen Sulphide however is caused by a bacterial problem but is also accompanied by a rotten egg smell, unlike hydrogen which is odourless. If it's air in the system then it must be coming from somewhere.
I take it it was another combi installed?
The sludge/magnetite needs to be removed. Ideally one would have a thorough powerflush, then suitable inhibitor added to the system afterwards, plus a filter on the return going back into the boiler. When the new boiler was installed the engineers should have taken into consideration the quality of the existing system water and pipework for foulness, you probably would have been better off separating the boiler from system side with a plate heat exchanger, this would have prevented any fouled water and debri from entering the boiler.