Air in radiators – running out of ideas !

[Poisonata]

This problem has been bothering me for some time now, I would very much appreciate any ideas people might have,

The system is a Worcester Greenstar 24i Condensing Gas Boiler (3 years old) controlling the Central Heating (sealed – top it up using a filling loop) and Hot Water (open vented, large insulted copper tank and water tank in loft which tops it up).

The air accumulates in two of the upstairs radiators (at the highest points) and the magnetic cleaner. Today I bled a total of a ¼ of a radiator full of air from the three points after the heating had been on for two days. The pressure gauge returns to 1 bar but after two or three days of use, its back up to 1.5 bar (cold) and a rebleeding is necessary.

The radiators themselves are old, 20 – 25 years (all copper pipe, no plastic push fittings). When the new boiler was fitted a power flush was performed, inhibitor added (prior to us owning the property) but I have no reason to doubt this.

First I emptied the system, water was discoloured (yellow-green) but only slightly. Topped up again and 4 litres of good quality inhibitor added (only requires 1 to 1.5 litres) but better too much than too little. Didn’t help even after several months of running the system. I also disconnected the filling loop just in case but this didn’t help either.

The helpful plumber suggested turning the pump from position 3 to position 2 (3 being the highest pumping rate, 1 being the lowest) and also adding 1 litre of leak sealant. This didn’t help either.

I cannot believe that in the knowledge the system was flushed and now has 3 times as much inhibitor as required that this is due to hydrogen gas (corrosion). The plumber seemed to think the air was being sucked into the system and I thinking due to the quantity of air bled, this is likely the case.

The boiler is annually serviced (as still under warranty) and seems to be working fine.

My expertise ends here, any suggestions would be most welcome.

If additional information would be helpful and/or photos please say.

My thanks in advance !

 

[ianmcd]

it is easy to test to see if it is Hydrogen or air that you are releasing, if it is hydrogen it will ignite be carefull just open the bleed valve a little and see if you can light the gas that is escaping, normally though if it is hydrogen it smells, I wouldnt have added leak sealer to a system that has been cleaned 3 times and if your WB is still under warranty you have voided this by adding leak sealer Im afraid

 

[45yearsagasman]

On a sealed pressurised system like yours, possibly up to 1.5bar (22psi) It's not possible for air to be sucked in.

 

[Poisonata]

I might then empty the system (again) as the leak sealer remains in suspension when 'wet' and flush this out (it didn't help anyway) then refill and retreat with inhibitor. It was the plumber who suggested/performed the leak sealer adding so I'm suprised you say it would void any warrantly. Thinking I might forget this incident !
Regarding the gas, I did wonder about doing this. I'm pretty sure it won't be due to the volume but to be sure I'll try it this afternoon and report back. In a way it would be easier if it was hydrogen as then I know I need to replace the radiators as they are beyond repair.
Thanks for taking the time to respond, I'll post back with my findings.

 

[Poisonata]

Thx again for a response. I did wonder by what means such a volume of air could be sucked in.
Guess this afternoons Hydrogen test may reveal the answer. Will repost.
Thank you again for replying.

 

[45yearsagasman]

Invert a can over the bleed screw and then attempt to light the contents. That will save setting fire to the curtains!

 

[Poisonata]

Working on the premise it is hydrogen, remedial action is to replace all the old radiators. I assumed that even if the rads weren't in the best condition, flushing the system then adding 3 times as much inhibitor as required would solve it. Is my thinking flawed ?
Thx again for taking the time to respond.

 

[dcawkwell]

Working on the premise it is hydrogen, remedial action is to replace all the old radiators. I assumed that even if the rads weren't in the best condition, flushing the system then adding 3 times as much inhibitor as required would solve it. Is my thinking flawed ?
Thx again for taking the time to respond.

If it is hydrogen it is an electrical problem causing hydrogen in the system.
No amount of inhibitor will stop that.

Ensure all copper piping has good earths so no stray electrical shorts can run through the pipes.

 

[ianmcd]

Quote

Do the system radiators need frequent venting?


If gas is accumulating in one or more radiators, it is important to determine whether the gas is hydrogen sulphide, hydrogen or air. Hydrogen sulphide is a product of bacteriological activity, and its occurrence is unusual. A toxic gas, it has an unmistakeable odour akin to rotten eggs which should not easily be confused with the smell of stale water or chemicals.

Hydrogen is a product of corrosion and this is common in new systems where an excess of flux has been applied, causing copper plating. Corrosion also occurs in older systems which have not been cleaned properly after the installation of new components, such as additional radiators or a replacement boiler.

If air is present in the system, this suggests that the problem is a mechanical one, such as pumping over or poor joints under negative pressure.


read the full article here

http://www.sentinel-solutions.net/u...irculation_Issues_in_Central_Heating_Systems/


Never heard of poor earth bonding causing Hydrogen formation in radiators but doesnt mean it cant, would have thought if that was a possibility it would have been mentioned in this article

every day is a school day as they say

 

[dcawkwell]

Quote

Do the system radiators need frequent venting?


If gas is accumulating in one or more radiators, it is important to determine whether the gas is hydrogen sulphide, hydrogen or air. Hydrogen sulphide is a product of bacteriological activity, and its occurrence is unusual. A toxic gas, it has an unmistakeable odour akin to rotten eggs which should not easily be confused with the smell of stale water or chemicals.

Hydrogen is a product of corrosion and this is common in new systems where an excess of flux has been applied, causing copper plating. Corrosion also occurs in older systems which have not been cleaned properly after the installation of new components, such as additional radiators or a replacement boiler.

If air is present in the system, this suggests that the problem is a mechanical one, such as pumping over or poor joints under negative pressure.


read the full article here

http://www.sentinel-solutions.net/u...irculation_Issues_in_Central_Heating_Systems/


Never heard of poor earth bonding causing Hydrogen formation in radiators but doesnt mean it cant, would have thought if that was a possibility it would have been mentioned in this article

every day is a school day as they say

You may remember from chemistry if you pass a current through water it splits the water into hydrogen and oxygen.
I have the problem on my hot tub. The sensor (two bolts about 2 inches apart) they are used to tell if the hot tub has water in measure a resistance. These rapidly erode into rust and nothing in a couple of months at which point the hot tub stops working and I have to replace them.

 

[Poisonata]

OK first thanks to everyone who has responded so far.

It is NOT Hydrogen Sulphide, I know this smell well and the gas from the system is odourless.

It is not Hydrogen, bled all three points slowly and the gas will not light.

As the original plumber suspected air is being forced into the system, how I have no idea. You expect water to come out of a pressurised heating system, not air in.

The pump was the first plan turning it down from 3 to 2. The plumber did say if we turned it down to the minimum setting it might not be adequate. The other suggestion is poor joints under negative pressure but I can't really think how this could occur.

Last thought the plumber left me with was the flange on the pump was of a design that it could possibly draw in air as it pumped. I didn't fully understand this and such a basic design error should be well know on these boilers if that is the case.

Anyone any thoughts ?

 

[Poisonata]

I'm considering calling Bosch to investigate the possibility air is being pumped into the system, I see no other explaination especially with the plumbers final thoughts on the matter.

Anyone disagree or anything else I can try.

Thanks alot in advance.

 

[TheGasMan26]

Firstly to0 much inhibitor is not better than too little, this can cause frothing/bubbling which in turn can cause sensors to not sense, Not sure though if it could cause excess air to build up.

Air can be sucked into a sealed system at certain points in the system, my first thing to try would be to close the AAV(Automatic Air Vent), and investigate the area near the pump as this is where air can be sucked into the system. The AAV should be under positive pressure but often seize.

How often are you having to top the system pressure up?

Is the pressure guage stable when the boiler go's from cold to max temp? check this.

Is your magnetic filter dirty? and if you clean it how long does it take to get dirty again?

Also if you are having hydrogen build up in the system this does not neccessarily require rad replacement, a "proper" powerflush using strong chemicals & an agitator will often sort this issue.

Good Luck.

 

[Poisonata]

Firstly to0 much inhibitor is not better than too little, this can cause frothing/bubbling which in turn can cause sensors to not sense, Not sure though if it could cause excess air to build up.

Air can be sucked into a sealed system at certain points in the system, my first thing to try would be to close the AAV(Automatic Air Vent), and investigate the area near the pump as this is where air can be sucked into the system. The AAV should be under positive pressure but often seize.

How often are you having to top the system pressure up?

Is the pressure guage stable when the boiler go's from cold to max temp? check this.

Is your magnetic filter dirty? and if you clean it how long does it take to get dirty again?

Also if you are having hydrogen build up in the system this does not neccessarily require rad replacement, a "proper" powerflush using strong chemicals & an agitator will often sort this issue.

Good Luck.

Thanks very much for this. Point taken about the inhibitor, in future I will add slightly more than needed but not an excessive amount if this is the case.

This is more like what I was after, the fact air can be sucked into the system as the plumber originally told me (at the pump). As the boiler is under warranty I will call Bosch. I just wanted to be sure I had a valid point/reason to call them and had excluded other possibilities so as to not waste an engineers time.

The system never needs to be topped up with liquid, just every two to three days I need to release air from the radiators to return the guage to 1 bar. After about 2 to 3 days of constant use (and left off overnight to cool) the pressure has increased to 1.5bar. Release air built up in 2 rads, back to 1 bar. Rinse and repeat three times a week.

The magnetic filter was cleaned on the last service 1 year after it was installed. The engineer remarked there was not an excessive build up and would not require recleaning until its next service. He commented that although the fluid was tinged with a slight green discolouration it was not enough for him to justify recommending any remedial action.

The pressure guage is stable, I have had experience with these sorts of guages in the past. That was one of the first things I checked, is the guage at fault here. It is not of that I am certain (confirmed by my other findings).

Very interesting (though not relevant to me) about hydrogen build up. I assumed once the rads had started to rot inside it was time to change. Now I fully understand the benefit of a proper powerflush.

Thank you to everyone who responded, especially TheGasMan26

 

[dcawkwell]

I'm considering calling Bosch to investigate the possibility air is being pumped into the system, I see no other explaination especially with the plumbers final thoughts on the matter.

Anyone disagree or anything else I can try.

Thanks alot in advance.

Bosch won't be the slightest bit interested. Nothing wrong with their boiler.