Central Heating Inhibitor life?

The manufacturer instructions normally give details.

I usually do a test of the inhibitor with a test kit once a year and add inhibitor if necessary. I drain, flush, refill and add fresh inhibitor every three years.

This seems to work well and I have kept systems in good and clean condition for over 20 years this way.

I originally had an open vented system and made absolutely sure that there was no pumping over or sucking down either. It's now sealed.

If you don't want to test, then in the absence of anything else it would be a good idea to add inhibitor every 18 months to 2 years. Overdosing doesn't really matter and Fernox is cheap in comparison with replacing system components.

No, but why would anybody not do anything when all that is involved is about 10 minutes and about £20 in inhibitor?

Why would anyone want to faff on and purchase and add extra inhibitor? Mine's been in (a sealed system) for 13 years and is as good as new. (I tested it recently.)

Overkill. 4 years is the usual time. A drain down is not necessary if the same type of inhibitor is use, e.g., X-100.

Because it degrades over time and that they are sensible, I would imagine.

The main point is to actually test. Most people don't even bother to do that and then wonder why their systems are full of crud and they are having to replace radiators and other system components.

It must have been substantially over the standard concentration requirement to begin with.

It was possibly double, it is easier to find the surplus when in the system rather than in my garage (unless (or until) it leaks.

That would assume that there has been no degradation in the inhibitor. There will be a greater tendency for this to happen in open vented than sealed systems. If the concentration of inhibitor becomes inadequate, corrosion will continue.

The Fernox web site states it has a life of 5 years Brian H

That's why 4 years is a good safe bet.

This depends on concentration and the amount of degradation, e.g. due to introduction of dissolved air into the system

It would be very foolish to fill the system and then leave any checking for 5 years.

And they are trying to maximise profits by selling it. You can probably add a factor of 2 or 5 to it.

On something like this, where there is an expenditure of £20 if a test indicates inadequate concentration of inhibitor vs. several £k at risk for guessing, regular testing or refilling is the correct course of action.

There is no such thing as a good, safe bet and certainly not in this case.

Of course, I suppose that letting the system deteriorate would help your counter sales of those magnetic crud catchers and radiators. There's much more to be made out of these than a few £ on inhibitor after all.

Matt, the average DIYer wouldn't know how to test the system water. He wants ballpark, and 4 years is ballpark.

This is another of your silly put downs.

Doing a job properly is doing a job properly no matter who does it.

One can buy a Sentinel Quick Test kit for £2.50. It comes with a small pot which is filled to a line with system water and then a tablet is added. It gives a yes/no indication.

Now I can appreciate that you might find that procedure challenging or beyond your means but I suspect that everybody else can manage perfectly well.

Your TRVs have lasted for 13 years? What make?

In our case, Danfoss. Still work just fine, installed in 1992.

I'd go with that

I know the manufacturers of inhibitor state that overdosing is OK on the instrustions but I have seen a letter from Honeywell to a customer who returned a 2 port valve to them that blamed overdosing of inhibitor for the premature failure of the ball in the valve.

Adam

Matt, it is 4 years.

Since when were you a doctor of chemistry rather than drivel?