Combi system.One radiator getting air in

Are you sure its air and not hydrogen?

As SimonG says above.
Your heating circuit should be under positive pressure so drawing air in is less likely.

SimonG said:

Are you sure its air and not hydrogen?

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SJB060685 said:

As SimonG says above.
Your heating circuit should be under positive pressure so drawing air in is less likely.

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Ah right. How would we know if it's hydrogen and what causes it? Sludge?
Inhibitor was put in the system, and even the copper pipework from the boiler to the first manifold (does that make sense) was brand new as we had the new boiler put in a new location.

whatsthenews said:

Ah right. How would we know if it's hydrogen and what causes it? Sludge?
Inhibitor was put in the system, and even the copper pipework from the boiler to the first manifold (does that make sense) was brand new as we had the new boiler put in a new location.

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Hydrogen is often described as having an eggy smell to it.
The next time you vent a radiator hold an upturned cup in the gasses path and capture a sample. If its Hydrogen it will pop when when you hold a lighter or match to it. If it doesn't ignite then it's just air.
Hydrogen build up in a system can be caused a couple of ways.
The oxygen content within the dissolved air within the water reacts with the iron radiators causing sludge and hydrogen production as by products.
Electrolysis, electrolytic reaction, galvonic corrosion however you define it can actually split the H2O into Hydrogen and oxygen. This is a basic explanation and if you're really curious then Google it because its quite in depth.
The quality of water in the system and heat can also increase the corrosion risk.

SJB060685 said:

Hydrogen is often described as having an eggy smell to it.
The next time you vent a radiator hold an upturned cup in the gasses path and capture a sample. If its Hydrogen it will pop when when you hold a lighter or match to it. If it doesn't ignite then it's just air.
Hydrogen build up in a system can be caused a couple of ways.
The oxygen content within the dissolved air within the water reacts with the iron radiators causing sludge and hydrogen production as by products.
Electrolysis, electrolytic reaction, galvonic corrosion however you define it can actually split the H2O into Hydrogen and oxygen. This is a basic explanation and if you're really curious then Google it because its quite in depth.
The quality of water in the system and heat can also increase the corrosion risk.

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I can understand how hydrogen would be produced if there's corrosion happening.
It stinks when we bleed the radiator and always has done, but I've been told before that the inhibitor smells. Is that not the case?

Inhibitors provide a protective layer on the internal parts of the system in an aid to help reduce the risk of corrosion but they don't last forever and depending on the size of the system they have to be dosed right to be of any affect and yes inhibitors do have their own smell.
I'm not saying it is hydrogen build up, I was simply explaining how to rule it in or out as its one possibility that must be considered in this situation.
Air can be drawn into the system in certain circumstances but with everything positioned where it is in typical combi systems the majority of the system is under a positive pressure, meaning with the boiler and pump running you would notice an improper airtight joint with leaks.

SJB060685 said:

Inhibitors provide a protective layer on the internal parts of the system in an aid to help reduce the risk of corrosion but they don't last forever and depending on the size of the system they have to be dosed right to be of any affect and yes inhibitors do have their own smell.
I'm not saying it is hydrogen build up, I was simply explaining how to rule it in or out as its one possibility that must be considered in this situation.
Air can be drawn into the system in certain circumstances but with everything positioned where it is in typical combi systems the majority of the system is under a positive pressure, meaning with the boiler and pump running you would notice an improper airtight joint with leaks.

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I understand. So maybe the installer didn't put enough inhibitor in , or didn't flush the system after installation before putting the inhibitor in? I think he told me he'd put a full bottle of inhibitor in, but we have 4 big 4000 ish BTU double convectors plus 4 smaller ones.
We've had a guy here doing the bathroom for the last 2 weeks. I did ask about the extra inhibitor after he'd drained down the system to put the new rad's in but he told me it should be fine, although the issue with the bedroom radiator had been around for the last 6 months at least, maybe longer and we just didn't realise because it's the smallest spare bedroom.
Due for a service next month so we'll get him here sooner
Just trying to find out about possible causes if it is hyrdrogen as I presume it's not good for the system and reduces the lifespan. If it's doing this to radiators what's it doing to the boiler? Does having a magnetic filter help?
Don't expect to have issues like this when you've paid out about £7k for a whole new "certified" heating system. Frustrating and doesn't inspire confidence.
Thanks for your help everyone.

A magnetic filter is required on all new boiler replacements and new installs, as well as a thorough flush and inhibitors added, so its a bit disheartening to here you paid 7k and there isn't one. Not only are most boiler manufacturers warranty void without but its also good practice and in my opinion more so if converting from an open vented system. As I said above sludge forms when oxygen within the water reacts with the iron content of radiators, producing rust and hydrogen as a result. This sludge is roughly 5 times more dense than water so likes to sit at the bottom of radiators and the system, this eventually causes cold spots in radiators, which leads to efficiency problems, as well as potentially rusting the radiator straight through. The thing with combi boilers is they're sealed systems, so every time you refill the system or drain down to make changes you're reintroducing air into the system. Now this being a sealed system it means without any air vents or ways to eradicate the air it will stay in the system and lead to corrosion, obviously there's a limit to how much corrosion can occur but if you are constantly refilling, draining down etc then you're just adding to it again and a magnetic filter will ideally start trapping this magnetite to be removed on routine services.
With regards to how corrosion can affect the rest of the system it doesnt help and frequently is the cause for plate heat exchangers and other components to fail. Also I might add an excess of flux from recent works and other substances can affect the water quality, this can and will corrode other parts of the system as well, although this largely comes down to passivation of metals and then certain acidic levels for each.
Sorry for the long winded response, im just trying to inform you of the problems we encounter far too often.

Any pictures of the install ?? . If the system has been drained then it needs new inhibitor added and venting to remove the air, if this is a recent occurrence?? then i would say it trapped air if not then the supply pipework or valves need checking it could also be a trv fitted in the wrong orientation not all valves are bidirectional and as a consequence can bang and rattle if water is passed through them in the wrong direction?? Regards kop

Flux can be a problem. The inhibitor manufacturer "Sentinel" tells me that it is quite easy to overload inhibitor with dissolved copper after which it won't work as well as it should.

Dissolved copper can be created if flux has not been removed from the system after work has been carried out. The traditional way best-practice way to remove flux is to carry out a cold and then a hot flush after any work is carried out. "Sentinel" tells me this isn't good enough and a flushing chemical such as X300 or X400 should be circulated for an extended period to remove flux.

In practice, especially in modification work, there often isn't the money in the job for this level of meticulousness, especially as draining systems can result in airlocks and consequential labour costs, though you would hope a new boiler installation would include a proper chemical flush to remove oils and fluxes from radiators and pipework respectively.

It would be interesting to know what brand of inhibitor has been used on your system. This information should be on your Benchmark certificate on the boiler paperwork.

Filters are considered good practice. On a technical level, they aren't needed so long as the system is clean and inhibitor is working correctly; they provide a safety net for instances in which corrosion begins to take place.

We don't know, however, that your issue is corrosion. It has been given as an idea on this thread, not a definite diagnosis. It is surprising how long air can sit in a system before settling out somewhere accessible. Definitely do keep bleeding the radiator as the less time the air stays in your system, the better.
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whatsthenews said:

Just trying to find out about possible causes if it is hyrdrogen as I presume it's not good for the system and reduces the lifespan. If it's doing this to radiators what's it doing to the boiler? Does having a magnetic filter help?
Don't expect to have issues like this when you've paid out about £7k for a whole new "certified" heating system. Frustrating and doesn't inspire confidence.

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Hydrogen, if present, won't harm your system. The concern is that the corrosion deposits could block the boiler heat exchanger. £7,000 for a new system may not be above the going rate, but that's not the issue. It also is quite possible for a competent installer to make minor mistakes as s/he is not in your house for the months it may take for very minor defects to become noticeable so that's not the issue either. Having not seen your system, I can't comment on the quality of the work, but my confidence in the installer would depend on how he or she responds to your informing them of the problem. Do they come and have a look or not?

Thanks everyone. Lots of information.
There is a magnetic filter on the system- sorry if what I wrote was misleading, I probably should have said "will the magnetic filter help?"
According to the commissioning report for May 19
" the system has been flushed an cleaned in accordance with BS7593 and boiler manufacturers instructions" is ticked
the system cleaner used was Plumb Centre brand and the inhibitor was Tower - 2 litres.
the filter is a Cali-Mag HF2
The re- pipe was done in September 19. Hopefully he cleaned the system and added more inhibitor.The First service date is September.
As I say-we may have been tardy in picking up on the cold radiator as it's the spare bedroom, so we've probably not been on the ball.
Can I ask what the valve is on top of the filter?

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Would be a manual bleed vent

Manual air bleed as mentioned above, the pictures don't tell us much I'm afraid it all looks tidy and as it should from what we can see , one thing you could try is remove the Thermostatic head from the cold radiator and push the pin down to check it's free ? then make sure the lockshield valve the other end is open vent the rad to remove any air ? then fire the heating up close off the rads that get hot and see if the cold rad becomes hot ? Note which end gets warm first ? Give it a try it may work if it does leave the heating on for 10 minutes or so then reinstate the other valves back to there original position. Good luck kop

Once bled the radiator gets evenly hot. I'll check which end gets hot first.
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it gets hot from the lockshield valve end

Can you post a picture of the trv on the other end there should be a arrow showing its intended direction of flow . Kop

king of pipes said:

Can you post a picture of the trv on the other end there should be a arrow showing its intended direction of flow . Kop

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Thanks kop and sorry for the delay. Arrow's pointing towards the radiator?

Then it's flowing the wrong way through the trv it could well be you trouble , needs draining and swooping over . Kop

whatsthenews said:

Thanks kop and sorry for the delay. Arrow's pointing towards the radiator?
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I'm no plumber (although I did work as a nurse in ICU and dealt with a lot of circuits on ventilators, kidney dialysis machines etc) but that seems wrong

king of pipes said:

Then it's flowing the wrong way through the trv it could well be you trouble , needs draining and swooping over . Kop

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Thanks kop. Going to check the other rad's. Elementary surely?

whatsthenews said:

Thanks kop and sorry for the delay. Arrow's pointing towards the radiator?
View attachment 45029

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Another arrow points away from the radiator (look under the 15). It's bi-directional. Thus this TRV can have the flow running either way without issue.

Ric2013 said:

Another arrow points away from the radiator (look under the 15). It's bi-directional. Thus this TRV can have the flow running either way without issue.

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We I'm a blind git I can't see it 😂

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Ric2013 said:

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Yes bud see it now , I would still swop it though probably change it to be honest I like em on the flow and balance on the lockshield but we're all different 😁👍 kop

king of pipes said:

Yes bud see it now , I would still swop it though probably change it to be honest I like em on the flow and balance on the lockshield but we're all different 😁👍 kop

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I like them on the flow too, on principle. That said, in my own house I've put at least one on the return, simply because if I had put it on the flow, it would have been shoved in a corner where it would have been hard to adjust and unable to sense the room temperature properly. Does it even make any difference, from a technical perspective, do you think?

I Don't know mate I am of the older generation and have always done it that way so it's hard to change your habits of 40 years, saying that if like you say its looks better cosmetically I would do it . Cheers kop