Adding inhibitor to CH system without draining

I've decorated a few rooms recently which has involved the draining and removal of radiators. I'm just
about to put the last one back on, however before I do this it struck me that I've probably diluted the
inhibitor. The towel rail came off a couple of times due to a leaky TRV.
I know the best approach would be to drain the system and refill adding inhibitor. I haven't drained
this system before (moved in earlier this year) and November doesn't strike me as a good time to start
experimenting with ways to clear airlocks.
The previous owners left no indication of what type of inhibitor may have been in the system.
My question is, am I safe to add more inhibitor in to the system without draining down?
TIA
Marc
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Marc Lee wrote:

Basically yes. If its a sealed system use the Fernox, squirt into a radiator stuff.
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Yes, but you don't say what system you have. If C/H cistern in loft just put some in there. If sealed or combi turn both valves off at any radiator. Have a few cartons ready then *hold valve with mole grip* and loosen the nut next to the radiator to drain off a litre or so. Now use a large radiator key to open up the radiator at the opposite end to where it's small air release point is. Use a funnel and rubber tube or anything you can get your hands on to put the inhibitor in. Open up valves, repressurise and vent rad when done.
Jon
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The system has a cistern in the loft, so I can just add the inhibitor through there and it will get drawn through when I put the last radiator back on.
My main concern is that there wont be a reaction between any existing inhibitor and the new inhibitor that I add to the system.
Does anyone have any views on Fernox / Sentinel? It's a fairly old system, not sealed with a cast iron boiler.
Thanks Marc
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On 3 Nov 2003 23:41:36 -0800, snipped-for-privacy@marc-lee.co.uk (Marc Lee) wrote:

I doubt whether there would be any reaction between different brands of chemical, but personally I would flush the lot and start again, simply to have a known situation.
.andy
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wrote:

I have the same thoughts on this.
I know there is a recommended minimum level of inhibitor for a CH system, but is it feasible that there might be a maximum level? So if you've got inhibitor in there already and don't flush it out the system could overdose on inhibitor?
Might sound implausible I suppose, but I expect heat transfer constants in water and in inhibitor to be different, so if you get the mix wrong.....
PoP
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wrote:

I'm not sure that overdosing (like double) with products like MB-1 is a particular problem - Fernox recommend a 4% dosing but don't warn about higher levels.
I did use some of their Alphi-11 product, which is a combined antifreeze and inhibitor for my garage workshop circuit, which is separate to the main house. While the pipework is well insulated, I thought that there could be circumstances such as pump or other failure where freezing could occur. With this product, there is a maximum dosing level of 40%, which is good to -22 degrees, although I used 30% which is good to -15 so a pretty safe bet. ALphi-11 is glycol based and distinctly more viscous than water.
The circuit in question is sealed, and since this is a liquid product rather than gel, it was necessary to come up with a means of delivery. Fernox sells an injector product, which is, in effect, a modified pumped garden sprayer. I bought a cheap sprayer from a DIY shed and modified it with suitable pipework to have an adaptor to fit onto a filling connection point. I was able to add the inhibitor (4 containers of it) quite easily this way and then added water to fill and pressurise it in the same way. To begin with, the two liquids didn't mix very well and there were circulation problems through the radiators - one getting hot, the rest not. Judicious operating of valves forced flow and mixing in the end, but it illustrates that additives can have an effect. I've kept the injection machine in case I have to do any work on the circuit. Since Alphi-11 is fairly expensive, I can part drain the circuit into a large container and the re-use the liquid. With some hard pumping, I can get 2 bar out of the sprayer to pressurise the system.
.andy
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