Central Heating Inhibitor life?

Sparks · 2006-04-02T00:05:54+00:00

How often should one drain the central heating system and refill, adding fresh water & inhibitor?Or is just adding more inhibitor OK or even needed?I changed a radiator a while ago, and the water in the old one was very clean, the system has not had anything added or removed for about 10 years.I went round and bled the radiators a few days ago (Haven't done this in probably 10 years, none of the radiators had gas in it.Should I worry that it is all about to fall to bits if I don't do anything!?Thanks :-)

Apr 02, 2006 27 Replies

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Andy Hall 20 years ago

I spoke with the technical departments of Fernox and Sentinel Performance Solutions and obtained similar answers from both of them.

- Longevity figures quoted are typical and not guaranteed.

- BS 7593 (Code of practice for treatment of water in domestic hot water central heating systems) calls for testing of inhibitor levels every year.

- If there is any tendency to water loss from the system, dissolved chloride salts in the make up water increase the load on the inhibitor. With an open vented system it is often not obvious that this is happening if the leaks are small - e.g. if the water is driven off by the heat.

- Closed systems typically have about a tenth of the concentration of dissolved oxygen as compared with open vented systems.

- If an open vented system is subject to any sucking down or pumping over, the load on the inhibitor is increased, apart from it being a serious problem anyway.

Given all of the above, the correct procedure is to test the inhibitor concentration annually. Taking bets on several £k of heating system is not prudent.

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David Hearn 20 years ago

I just drain a small amount into a jam jar and put a nail into it. I put the same amount of fresh water into another jam jar with a nail. I leave for a few days/weeks and then compare the two. Water from central heating system showed no corrosion to the nail. Fresh water nail was all brown and rusty.

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Chris Bacon 20 years ago

Is there an easy DIY test?

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Andrew Gabriel 20 years ago

Run some into a large jam jar with a good sealing lid. The ideal time would be when it's not been hot for a while but has been pumped around (which will be maximum oxygen dissolved, if there is any). Add an iron nail (two if small) and a copper coin. Make sure the nail is bright and shiney, and not protected by a layer of oil. Seal the lid and leave the jar with the coin and nail touching. If there's no corrosion of the nail after a couple of weeks, the inhibitor is working. (It also works without the coin, but I think the coin speeds things up by generating some galvanic action.)

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