Gassing in CH won't go away.

[johnkirk]

I have an irritating problem which I am hoping has a solution.

When the water leaving the boiler reaches 70C and higher, gas bubbles form, which causes noise in the first available radiator.

3 - 4 months ago the system was flushed, Fernox F3 added and left in for weeks, then flushed again repeatedly. The boiler heat exchanger was also de-scaled using 13% sulphamite for 3 hours, flushed again, then the system refilled with clean water with the correct dosing of Sentinel X100 inhibitor and Sentinel X200 noise reducer.

In spite of all this bubbles form at 70C and above.

I keep venting the system manually, mainly from the magnaclean unit and the 2 noisy radiators.

Does anyone know what I can do next to eliminate the formation of gases, which I presume is not air but the production of hydrogen being released from the water?

The CH comprises a sealed heat only boiler (Potterton Netaheat Profile), expansion vessel kept at 2 bar, and HW cylinder via a mid-position valve. There are 13 radiators. Prior to cleaning there was a small amount of kettling at the boiler but it is now entirely eliminated by the sulphamate descaling and X200 subsequently added . Prior to flushing the water was very dirty with magnetite, but now appears clean judging by the clear water seen when bleeding the radiators and removing the magnaclean element.

I want to allow the boiler to reach its maximum of 82C when necessary, and not have to restrict the flow temperature to 70C in order to avoid gassing. Presumably this is not asking too much?

Is installing the Spirotech aerator the way to go, or are there other things I can do to stop the gassing?

Would really appreciate any advice on this, and thank you in advance!

 

[ALCPlumbing]

You could put some automatic bleed vents on the nearest radiators and an automatic air vent on the pipework near the boiler. Have you tried running the boiler at a lower temperature?

 

[doitall]

Think the OP is missing some logic,

Hydrogen has a very strong smell of rotten eggs.

2bar is too high at cold start, what is it when the heating is at temperature.

Hydrogen is cause by corrosion, have you flush the radiators out separately.

Last and most likely you have a leak.

 

[JohnD]

How much sediment are you getting out of the Magnaclean, and what colour is it?

Is the amount reducing?

Are you sure the filling loop is closed and the pressure relief valve is not dripping?

 

[johnkirk]

It may not be hydrogen, but the point is it's unwanted gas.
Hot pressure is 2 bar, cold is 1.8 bar.
The intention is to stop the noisy bubbles forming in the first place, and not have to hear the bubbles causing noise on entry to the radiator(s).
No leaking anywhere.
Air seperators only remove a fraction of the gases. Exception could be Spiotech's aerator (or is it called something else?). Costs about £100 I think.

 

[Agile]

Hydrogen has a very strong smell of rotten eggs.

Ever since man has been created, hydrogen has been odourless!


It would have been before man too but there would not have been anyone there to smell it.

 

[johnkirk]

JohnD, small quantities of black magnetite at Magnaclean, and yes reducing on every check, albeit slowly. I suppose the residual magnetite may be causing the gassing. Doesn't the X100 inhibitor stop this?


Pressure relief valve not leaking.

 

[doitall]

It may not be hydrogen, but the point is it's unwanted gas.
Hot pressure is 2 bar, cold is 1.8 bar.
The intention is to stop the noisy bubbles forming in the first place, and not have to hear the bubbles causing noise on entry to the radiator(s).
No leaking anywhere.
Air seperators only remove a fraction of the gases. Exception could be Spiotech's aerator (or is it called something else?). Costs about £100 I think.

If it isn't hydrogen, it isnt gas, have you tried lighting it, (you can catch it in vessel)

If it isn't gas you have a leak, and a system fault if other.

How are you topping the pressure up in the system.

What type of cylinder and approximate age.

 

[doitall]

Hydrogen has a very strong smell of rotten eggs.

Ever since man has been created, hydrogen has been odorless!

The hydrogen is produced by corrosion and will smell very strong (rotten eggs is a good likeness)

Can also be produced by electric currents.

 

[johnkirk]

I suppose my question relates to whether it is ever possible chemically to have clean tap water with the appropriate additives in the system that ensures no bubbles form at high temperatures like 85C (or perhaps even 90C if/when the time comes that the existing boiler is replaced by an Intergas one).

 

[johnkirk]

The pressure rarely needs topping up, in spite of the regular bleeding. Only small amounts of gas are bled off. If I do need to top up it is via the mains water using the loop hose - undo the tap at each end, then close them.

The system pressure was initially set at about 2 bar cold. That was 3 - 4 months ago. It is now 1.8 bar cold, and 2 bar when hot. No water has needed to be added during this interim period, in spite of opening the magnaclean unit 4 times and bleeding off the air from it each time.

Just to repeat, there are no leaks anywhere.

 

[doitall]

Missing an important part of the process John.

The bubbles are from the fresh water when the system is filled and heated above a certain temperature, however after about a week of use the air in the water is all gone so no bubbles unless fresh water is being introduced.

The sealed heating and hot water should be separate and will only mix if there's a fault or breakdown of part of the system.

 

[johnkirk]

I'm trying to understand why I still have the problem 3 months on, which I expected to disappear after the first week or so when the fresh water was added.

 

[johnkirk]

Perhaps I need to wait longer, into winter, for the system to get much more use. Also, the system volume is quite large, at 105 litres, when pressurised to 2 bar, so maybe I need to wait till mid-December and then re-assess

 

[johnkirk]

The cylinder is copper, indirect, about 12 years old.