CH corrosion inhibitor

[Bob Smith]

How do I check if inhibitor is in my system, and if it it at the right concentration?

TIA

Bob

[Andy Hall]

You can get a test kit for example from Fernox - available from heating merchants.

It doesn't matter particularly if you overdose the inhibitor.

.andy

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[BillR]

One way, from Frenox I think, used to be:- let some fluid out of the system into container. Dilute it, say 10 to 1? Add a mild steel nail. wait a week, if any rust on nail inhibitor needs renewing

[Set Square]

Is it ok to dip some out of the header tank in a non-sealed system?

What's the rationale of diluting it?

[stefek.zaba]

Wouldn't have thought that would tell you much about the concentration of inhibitor being pumped round the rads; in the absence of leaks and of pumping-over, you could have a big difference between the composition of what's in the header tank ready to refill any losses, versus what's going round and round the rads (including the dose of inhibitor we hope was poured into the header tank early in the filling process, but got flushed through by more water coming into the tank during the refill).

Presumably to represent the difference between (a) "rusting power" of the rad-water at 80degs versus room-temp, at which you're doing the test, and (b) doing the test over just one week, rather than the year or so you're likely to leave it if the test says "OK" ;-) Roughly, if the rad-water diluted down fails to let the nail rust, then there's likely to be enough inhibitor in the radwater to keep the rads from rusting under the more demanding conditions of higher-temp and longer-time. It's quite a challenging test if you dilute with freshly drawn tapwater, mind: there'll be lots more dissolved oxygen in the diluting water than in the circulating radwater.

(Reminiscence time: the guy who taught me chemistry when I was about 12 or

13 years old had a rather convincing "look, you need air *and* water to get nails to rust" demonstration: he had a nail in a test tube sealed with rubber-bung and wax, in which a still-bright nail had been placed in freshly-boiled (thus oxygen-expelled) water about 20 years previously...)

Stefek

[Christian McArdle]

If you haven't changed it in 3 years, it needs doing anyway. Flush it out and put new stuff in. As it only costs a tenner and is simple to do, I'd probably do that anyway if I was worried about the concentration.

Christian.

[Bob Smith]

Not worried, just that we moved in 6 months ago, and don't know what is in there.

The rads are still full of water, and the bottom of the rads in the middle gets hot, so I am probably OK.

Bob

[Christian McArdle]

Replace it then. Better to spend half an hour and ten quid now, than run the system with inhibitor that probably hasn't been changed in a decade assuming it hasn't been diluted out of existence.

Christian.

[Andy Wade]

Err, why? Fernox's literature says "one treatment of Fernox MB-1 or CP-3 can last in excess of 60 years with possibly only minor topping-up every

10-20 years."

[Bob Mannix]

Well it uses the word "can", ie it might not. (cf silicone sealant guaranteed for 25 years, ho ho). OTOH I would agree, for a system where you know what has happened to it since filling, I would leave it a lot longer than 3 years (assuming I hadn't done any work on it). If I moved house I would probably flush and refill if the Fernox label was three years old, as you don't *know* what has happened in the intervening period.

[Andy Hall]

I test mine once a year and in a system that's a bit over 100 litres, it gets to the marginal point on needing topping up every third year, so I drain the appropriate amount of liquid and add fresh inhibitor - more recently the gel stuff.

.andy

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[Alan Campbell]

How do you get on with the gel (I assume its the stuff that you inject into a rad).

I tried it a few months ago. I had already purchased the gel then decided to drain the whole lot down anyway. While the system was empty, I added the gel (put a bit in 4 rads different rads, just to make sure it was going to get spread around) then refilled the system. I found that when I came to bleed the rads, quite a bit of the gel was forced back out of the bleed valve by the trapped air.

Alan

[Andy Hall]

Well....

I don't follow the instructions on the tube, which basically tells you to inject against the pressure of the system.

Instead, I select a radiator large enough to take the tube contents, turn off both radiator valves and drain the radiator. I have lockshield valves with a drain c*ck on the radiator side, so it's easy. Otherwise it would be a case of drain using a union.

I then inject the stuff in, close the vent and open the radiator valves. Then run the system for a couple of hours and vent. Only water comes out.

Perhaps hot water helps it to dissolve?

.andy

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[Charlie]

I've got to be honest I bought Fernox Cleanser and inhibitor about 7 years ago when I first moved in and was revamping the CH. Once I'd moved everything where I wanted it I refilled and I didn't use either the Cleanser or the inhibitor. And to be honest whenever I've been working on the system since it never occurs to me to use them until after I've refilled and bled.

Although the contents of the system is rather black I've never had any trouble. What exactly would I be protecting myself against? I know the man who was here before me and he never used any either. Most of the rads and the boiler are nearly 30 years old.

I was once told by an ageing plumber that "that stuff" shouldn't be used in old systems as it is rather severe (I think he meant the cleanser) and is just as likely to cause holes to appear at any point of weakness, for example where the bottom of the radiators are jointed. Maybe thats at the back of my mind and accounts for why they still sit at the bottom of a cupboard in the kitchen. Any truth in his fears?

[Andy Hall]

Corrosion of the radiators and the boiler heat exchanger.

It is possible that the radiators are of a period when thicker metal was used.

It would be prudent to budget for replacement.

It depends on the cleanser. Most of them are fine as long as you follow the instructions. With inhibitor, the only issue is if you use one not suitable for aluminium and the heat exchanger is aluminium.

If the system is in that state, you are going to get a leak in due course anyway.

Old wive's tale. .andy

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[Ed Sirett]

Yep, The universal cleaners, desludgers and inhibitors should not cause any further damage to the system.

Acid descaling chemicals _might_ remove some usefull leak hold limescale in older systems, but if things are that marginal then it's time to consider a major overhaul.