Hi,
I posted here recently about draining my HW cylinder and it was suggested that I could siphon the water out of the top. When I tried to do this, I found that I could not fit a hose pipe into the cylinder because the bore of the outlet was reduced with scale. Here's an update:
I bought a 2kg tub of Fernox DS3. This was a bit of a lottery as I didn't know whether I would need 200g, 2kg, 4kg, 6kg, etc. Is there any clever way to estimate the requirement?
The instructions on the side of the tub are rather brief; they say there are more detailed instructions are inside but I found they said pretty much the same as those on the side of the tin. I found more comprehensive instructions from an ebay seller!
The manufacturer's version said to mix 2.5-10% to form a paste. Since I was adding to a 200L cylinder, I did wonder if I could miss this step out and just pour the granules directly into the cylinder. What do you think?
I did as the manufacturer suggested. After all, I would not have been able to shake or stir the cylinder to aid dissolution if the granules had not dissolved!
I diluted them 10% but it did not make a paste; it was a liquid. Perhaps I got the formula the wrong way round; perhaps the paste is nine parts crystals to one part water rather than the nine parts water and one part crystals that I used? It doesn't matter as a paste would have been difficult to pour into the cylinder.
The instructions recommended opening the taps to replace spent DS3 with fresh DS3 to clean the pipes. I observed the colour change from the green back to yellow.
Since I was still seeing green at the end of the process, there must have been some scale left.
I had used about three quarters of the tub in my original dosing, so I decided I may as well use the rest. Because there was less this time, the colour as paler and I found it harder to discern the colour change. I'm still not sure whether I was seeing yellow or green at the end!
I don't want to remove the immersion heater to have a look because I have read here about cross threading the heater or buckling the cylinder, necessitating expensive cylinder replacement. However I do know that looking into the 22mm inlet at the top, which was previously obstructed, it is now clear and I am able to get a hose in, so there has been a big improvement there at least.
Whether I will go to the expense and time of doing all again to remove even more, I do not know.
What puzzles me is that in my kettle, scale is white. Isn't it calcium carbonate? Whereas that at the top of the cylinder was green, implying copper carbonate. Could it be that this was not scale from hard water after all?
In the earlier thread flanges were discussed. I had a read about flanges on the internet and it was suggested that they improved the flow to showers as they did not suck any air in. I am puzzled by this. Doesn't the vent pipe have water to the level of the header tank? If the header tank is six feet above the cylinder, would a pump suck all six foot of water away to get to the air?
There's an interesting picture (diagram B) in this Wickes' leaflet. It shows bubbles rising in the cylinder, which I think is much more likely. I wonder whether bubbles are released during heating, like they are in a kettle, and whether the carbon dioxide in these bubbles has reacted with the copper to form the deposits. What do you think? Any plumbers or chemists here?
The next step is to run a more direct and insulated pipe to the kitchen so that it doesn't take forever for hot water to get there.