Not enough Fernox?

[autolycus]

Hi,

At the weekend, I had to drain down our (open vented) central heating system.

When I refilled it, I bought a bottle of Fernox and added a slug of it every 20 seconds or so as the header tank was refilling - and hence (I presume) as the header tank was in turn refilling the rads.

By the end of the process, the water in the header tank was a nice pale orange colour, as were the samples of water that I bled out of a few of the rads.

Half an hour or so after this, I noticed that the system was venting hot water into the expansion tank for a good 10-15 minutes or so. This water was also suitably amber in colour.

That evening, I took further samples of water from the radiators and the colour still showed what I took to be a decent amount of Fernox in the system.

Today (4 days later) I was up in the loft and noticed that the water in the header tank looked very clear and colourless.

I checked the radiators and the water in them now has no discernible colour.

So my questions are as follows and I'm hoping someone can offer some help please:

1. Is there a simple way to check if I have enough Fernox in the system at present?

2. If I don't have enough, how urgently does the situation need fixing? Should I rush out immediately in the morning and buy some more Fernox or can the system cope as it is for a week or so?

3. What would have caused the colour of the water and the amount of Fernox in the system to change so much since Saturday?

4. Did I do something wrong when refilling the system at the weekend?

5. Is there an easy way to increase the concentration of Fernox without having to drain down the whole system again?

6. Given that I need to get the boiler serviced in the next week or so, should I just leave all this for an expert to deal with at the same time?

Thanks in advance,
David.

 

[bengasman]

in case of doubt, add another bottle, it is only 15 quid. it is hard to have too much in it, but too little will proove costly in the long run

 

[autolycus]

Not fussed about the £15 to £20 for another bottle. But what is the easiest way to add it? Can it be done without draining down the whole system?

And if I do have to drain it down again, how can I ensure that this time the level of Fernox stays high enough. I don't really want to be draining down the system and adding another £15 worth of Fernox every 3-4 days.

 

[bengasman]

if the system is empty, you stick in the tank the moment you start filling up. if it is a top up, just add the bottle, personally i would not bother draining any. trun the pump on max for a day if you want to speed up the mixing, as this usually causes a bit of overflow back into the tank.
if you have to drain the system completely, you have to add the full dose again i'm afraid

 

[autolycus]

if the system is empty, you stick in the tank the moment you start filling up.

That's what I did last time, but now after a few days the Fernox has "disappeared"......

if it is a top up, just add the bottle, personally i would not bother draining any. trun the pump on max for a day if you want to speed up the mixing, as this usually causes a bit of overflow back into the tank.

But if it doesn't cause any overflow, then the extra Fernox will just sit in the header tank, won't it?

 

[bengasman]

no, the normal working of the heating will mix, will just take longer

 

[autolycus]

As an alternative, could I use this technique:

//www.diynot.com/forums/viewtopic.php?p=120492#120492

to get extra Fernox into the system quickly - even though I have an open vented system rather than a sealed one?

 

[JohnD]

You know where the drain cock is, right?

tie up the ball valve

tip in your bottle of inhibitor and stir it in

draw off a bucket of water from the drain cock

go up to the F&E and observe that a bucketful of water has gone from it down into the system.

If you care about the 1% of a bucketful of Fernox, tip the bucket back in the F&E before you untie the ball cock.

Be aware that if your system is full of clean fresh water, it might be because it has a leak and has been topped up with fresh, aerated water.

Fill the F&E to a couple of inches above the ball-cock level, look at it a few days later and see if it has dropped.

the ball cock level should be set only a couple of inches above the F&E pipe connection near the bottom to allow for plenty of expansion.

p.s. it should not be venting hot water. there is something wrong.

 

[autolycus]

You know where the drain cock is, right?

Yes

Be aware that if your system is full of clean fresh water, it might be because it has a leak and has been topped up with fresh, aerated water.

That was part of my original questions really. I don't know for sure that the system IS full of clean fresh water - it just doesn't look orangey like it did at the weekend. Should I be able to "see" the Fernox in the system?

p.s. it should not be venting hot water. there is something wrong.

This only happened for abut 10 mins or so after the system was refilled at the weekend. It is not constant and has not happened since then as far as I am aware.

Does that one-off 10 minute venting really indicate a problem?

 

[JohnD]

might possibly have been an airlock that is now cleared.

but try the water level test.

depending on the space in your F&E it is sometimes possible to put a glass jar under the ball valve and the vent (that will spill over into the tank) so you can see if anything has happened when you weren't looking.

crystal clear water in a F&E is unusual and suggests it has been topping up.

IIRC Fernox make a "tracing dye" that will harmlessly colour the water to help you detect leakage.