CH system losing water

[osh]

First post on this forum and not a plumber by trade so apologies for the long ramble. I have a little technical knowledge so have a general understanding of CH sytems and can undertake basic maintentance on my own.

In Jan 2010 I had my old CH/hot water completely overhauled. I have a Vaillant Ecotek system boiler (on the 2nd floor) with a Heatrae Sadia Megaflo unvented mains fed indirect heated tank (on the first floor). The existing heating pipework for the ground and first floor was hardly touched (save for two new radiators installed on the ground floor), and seems to be in good condition throughout. At the same time we fitted a heated towel rail in the 2nd floor bathroom and Thermaskirt heating in the 2nd floor bedroom.

Last winter the automatic bypass Valve (Tower brand) failed. This was replaced with a different brand and at the same time an automatic air release valve was installed in the pipework near to the boiler.

Recently I have noticed that the CH system is losing water, noticeable in the towel rail as it is the highest radiator. I have bled it, and three weeks later it's at the same level. The most obvious answer is a leak in CH pipework, but I was hoping that there might be an alternative reason what could be causing it.

What I find strange is why the air in the system doesn't bleed out of the ARV, causing the system pressure to drop. Also, can anyone tell me what setting the ABV should be set to? At the moment it's at the lowest setting.

 

[osh]

I understand that. What I don't understand is why, after I bleed, it doesn't return to the original pressure that it was set at. It's as if some water has drained off somewhere.

 

[Best]

I understand that. What I don't understand is why, after I bleed, it doesn't return to the original pressure that it was set at. It's as if some water has drained off somewhere.

If the pressure drops, you have loss of water somewhere, slight or otherwise. Microscopic leaks from rad valves or brass joints are common leaks. A PRV will open & close & water will be lost if system pressure too high when boiler heats.

 

[MattWeth]

Assuming that the 'air' you have in your system isn't actually air but hydrogen (try lighting the gas that comes out of the bleed valve - you may be surprised!), then some water is being chemically turned into hydrogen and oxygen through the formation of oxides (rust). The hydrogen that's left is what you're bleeding out.

Also, microscopic leaks on the negative side of the pump can draw air in while not letting water leak out...

 

[osh]

Assuming that the 'air' you have in your system isn't actually air but hydrogen (try lighting the gas that comes out of the bleed valve - you may be surprised!), then some water is being chemically turned into hydrogen and oxygen through the formation of oxides (rust). The hydrogen that's left is what you're bleeding out.

Also, microscopic leaks on the negative side of the pump can draw air in while not letting water leak out...

That makes most sense. I did post earlier in the thread (a while back!) that the air was highly flammable, so we already know that it's hydrogen.

 

[osh]

Oh dear, seems that the system has sprung a leak overnight. Total loss of pressure.
Will need to flush out, and fill up with Fernox F1 and F4.
Can anyone tell me if there are any issues with putting them in together at the same time? Or is it as straightforward as it seems?

 

[MattWeth]

Check the expansion vessel (see if water is discharged from the schrader valve) and see if there is evidence of water at the relief valve discharge.

 

[osh]

I dont think I have an expansion vessel. Have a Megaflow. Are you talking about the open sided valve on the side of the Megaflow?

 

[Mike Jackson]

Oh dear, seems that the system has sprung a leak overnight. Total loss of pressure.
Will need to flush out, and fill up with Fernox F1 and F4.
Can anyone tell me if there are any issues with putting them in together at the same time? Or is it as straightforward as it seems?

I would initially top up with plain water and see if the pressure holds. Of it does try running the system and watch the pressure gauge, if it rises rapidly to above 3 bar your expansion vessel has lost it's charge pressure and will need re pressurising or replacing.

If the water pressure just drops rapidly you have a serious leak. F4 will not cope with a large leak so you will need to find the location of the leak. With the amount of corrosion that has been happening in your system a leak is quite likely.

Once you have discovered and resolved the problem of this larger water loss I would then deal with the corrosion issue. Just adding an inhibitor is unlikely to stop corrosion on this scale and the system needs a decent flush with F3 or similar before you add F1. Make sure you use the correct amount of inhibitor, one bottle is generally enough for 10 SINGLE radiators. Count double radiators as two.

 

[kay-jay]

good advice mike!

 

[osh]

In the end due to lack of time I just did a very basic flush (not very effective), and refilled with F1 and F4 last night. At 12.30 last night I left it at 1.1 bar and this morning at 6.00 the heating came on so it seems the pressure held overnight. Don't seem to have any problem with the pressure rising rapidly so I can only assume it is some sort of leak.
Are you saying that if I don't use F3, even with the correct amount of inhibitor, it will still corrode?
Does F3 need to be flushed out or can it be left in the system until the next flush? Don't fancy draining out £40 of product....

 

[kay-jay]

In the end due to lack of time I just did a very basic flush (not very effective), and refilled with F1 and F4 last night. At 12.30 last night I left it at 1.1 bar and this morning at 6.00 the heating came on so it seems the pressure held overnight. Don't seem to have any problem with the pressure rising rapidly so I can only assume it is some sort of leak.
Are you saying that if I don't use F3, even with the correct amount of inhibitor, it will still corrode?
Does F3 need to be flushed out or can it be left in the system until the next flush? Don't fancy draining out £40 of product....

There are other cheaper products. Calm cleaners and inhibits are good and shouldn't cost more than 8 quid a litre at a local merchants. Read the label. Some cleaners can be left in two ti four weeks. You should add oneof these and use ch as much as possible then drain and flush the system and then add the inhibitor on refill.

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[kay-jay]

That should read calmag cleaners and inhibitors .....damn predictive text

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