How much inhibitor in a very small system?

[Lucky Luke]

Hi, experts. I am considering having a new boiler installed (a Vaillant EcoTec Plus 824), following a long period of trouble with our existing boiler. In our house, there are only three radiators (without going into our reasons for this arrangement, this is the way we want it to be). The engineer that installed the existing boiler did not put any inhibitor in the system (at the time, I was in complete ignorance about central heating). I believe that he ought to have done this, and charged me for it, rather than leave me to find out, the hard way, about the need for inhibitor. He never even advised me, and I knew nothing about the need for radiator protection. Anyway, the engineer that I am considering employing to install a new boiler did mention it, and says that this would be covered by the cost of the installation. What I should like to know is about how much inhibitor should be put into our system. I mean, naturally enough, the new engineer will want to cut down on his expenses, however honest he is, and, if he is anything like the first one, he might put in even less than the minimum, and I would not know..). I need to be certain that the new boiler will have the best start, so, in his quotation, I want the engineer to specify the amount that I ask him to put in, to be certain of having no corrosion problems, later.

I have no idea what a correct amount would be for our system, but let me say that the total area of our (double) rads is only six feet 7 inches by two feet (about 13 squ. ft.) This may seem to be a bit laughable, but we are happy with this arrangement. It heats the hall, the kitchen and the bathroom, and we have other heating in the other rooms.

Also, assuming that no water were added afterwards (for example, through topping up the pressure), how long would the inhibitor be good for?

With thanks for a helpful and informed answer,
A.W.

 

[oldbuffer]

Half a litre is probably enough, but stick the whole (1 litre) in - it won't do any harm.

 

[Lucky Luke]

Half a litre is probably enough, but stick the whole (1 litre) in - it won't do any harm.

Thanks for that, oldbuffer! That's exactly what I shall do. Just another thing, though. How much anti-freeze inhibitor would be enough for our system for both purposes, on the basis that, even in the coldest winter, the temperature is not likely to fall below -10°?
A.W. (another old geezer)

 

[oldbuffer]

Don't know from experience. Brought up in Lancashire but now living in London - so freezing rarely an issue. If you look up Sentinel X500 on https://www.sentinelprotects.com/uk...ng-systems/sentinel-x500-inhibited-antifreeze it looks as if you'd need about 30 litres for the average system to protect down to -10. However, as yours is a small system (unless you have very long pipe runs) you'd probably need less.

However, provided the property is normally occupied, I'd suggest you could rely on normal frost protection of frost thermostat plus pipe thermostat, although I think the Vaillant has some built in protection. You would then only be at risk in the event of power failure or gas supply failure, and if these were extensive, you could drain the system (and boiler).

 

[terryplumb]

You should also lag the mains cold pipework that goes to your boiler ,if its still in the out house. How do you know that no inhibitor was put in the system ?

 

[Lucky Luke]

. How do you know that no inhibitor was put in the system ?

Because the system (well, the boiler heat exchanger) got a slab of muck stuck to it and the DHW water would not heat up. (it was removed thoroughly by a power-flush, but before that, it was manually cleaned by the man that fixed the problem). When the muck came off, the DHW worked. This happened about two years after the boiler was installed.
A.W.

 

[terryplumb]

That does not mean that there was no inhibitor .it cant stop oxidation ,it just inhibits the process.

 

[Lucky Luke]

That does not mean that there was no inhibitor .it cant stop oxidation ,it just inhibits the process.

Terry, I didn't know that. Perhaps I misjudged the man, after all. Thanks for the clarification.
A.W.