Thermal Store Corrosion Protection Question

[DeadJoe]

Hi, All.

I have a 300L stainless steel thermal store feeding 5 radiators (also there is a direct connection to a woodburner, which is not stainless steel) - I guess maybe 400L in total. I'd like to add some corrosion protection - when the system was commissioned a couple of years ago, it was easy enough to get 5 bottles of Fernox FI into it (at great expense - it's pricey, isn't it?), but now I am a bit stumped.

How do I get the Fernox into the system? I think pouring it into the header isn't going to work - I can't see how enough of it would get into the system. Am I supposed to pump it in somehow through the drain valves?

Also, is Fernox the way to go?

Any advice would be welcome.

 

[gas4you]

Isolate cold feed to ball valve in header tank, then drain some water out of thermal store. When a few litres drained out, add inhibitor to header tank, open cold feed and let it fill up as per normal.

 

[kevplumb]

however much you put in plus whats in the header

drain out

header at top

drain at bottom

bugger

beat me dave

 

[gas4you]

 

[DeadJoe]

Trouble with that is that the feed to the store runs from the side of the header, which is in fact the old cold water storage tank. If I drain the header tank down to the pipe leading to the store, I am still dealing with a fair few litres of water in the bottom of the header tank. Anything I pour in will be pretty well diluted before getting anywhere near the store...

 

[kevplumb]

err its gonna be diluted anyway

its not meant to be full strength

it's the system water

or should be

if your not sure hoy another bottle in it won't hurt

 

[DeadJoe]

I'm not sure I'm explaining this very well...

I understand it gets diluted anyway, but I am anxious that it will get diluted in the header tank, and the majority of it will just sit in the header rather than getting into the system where it can do some good.

If I lower the level in the header as much as possible by draining water from the heating system, I am still left with maybe as much as 50 Litres in the header, because the pipe to the thermal store exits from the side of the header, about half way up.

This means that if I add (say) 5 x 1 litre bottles of inhibitor, it is going to be diluted in the header to 1/10th of its original strength. When I refill the header, maybe one half of that diluted inhibitor will get into the thermal store and be further diluted by the 400L in the system. The majority of the inhibitor is going to sit in the header, where it does no good at all...

Does that make any sense? Or am I just obsessing for no good reason?

 

[kevplumb]

ok even if you could get it directly into the store
sooner or later its gonna finish up in the tank due to expansion and contraction of the water

 

[DeadJoe]

Ah - that helps a bit. If expansion and contraction means that the volume in the header tank slowly mixes with the volume in the store and radiators, then there is no problem, I guess. I hadn't allowed for that, thinking that all the header volume is doing is providing a bit of pressure in the system as a whole. But if the two volumes slowly mix by expansion and contraction through the fill pipe, then there isn't much to worry about...

 

[kevplumb]

only diff is if you do drain some water out it will get into the system a bit quicker

 

[DeadJoe]

Thanks, guys - I'll relax, drain the header, and just pour it in. Cheers!