Attic header tank dirty

nordicb

Hi All,

Hope everyone is well, hope for advice.

A year ago I have flushed heating system and replaced all radiators (7 rads), installed magnetic inline filter, refilled with tap water and added 2 bottles of Sentinel X100 to soften the water. Everything seemed to be ok, but half a year ago I noticed some slime in the header tank, but kinda left it as is since the water in the tank was transparent. However, half a year later, today, I noticed that tank water is pitch dark, actually nearly black, not brown. The mag filter is rather clean, therefore I think it is most likely bacteria or fungus. Would you know what I missed in the past and what could be done now? I was thinking to flush the system again, but this time to add some biocide? I find it hard to find the biocide in shops for some reason, say Sentinel X700 or Fernox F7.

Any advice is appreciated, thank you!

John.G

With your system running normally look into that header tank and see if there is any pump over through the vent or movement in the tank which could be pump back through the cold feed, also feel if the tank is hot/lukewarm after the heating is running for a few hours.

nordicb

Hi, and thanks for the reply.

The vent is just a U shaped pipe connected to the header tank bottom outlet to heating system, open end pointing back into the header tank. Cold water supply is via a float valve, which I have raised permanently to disable any feed of fresh water.

The water seems to be same temperature as the attic. Attic is insulated and doesn't get as cold as outside. Header tank in the past used to be without cover, but I have covered it with just a light plastic bag. I have a feeling the X100 may have made it suitable for fungus to develop, water smells earth/soil. I did notice water got very different first day I used X100. Perhaps 2 bottles were too much, not sure.

Water never gets hot in the system, oil burner is set to max 60'C, but it never reaches that because of room thermostat. Any of this could contribute?

Thank you

John.G

Is it something like mine, a combined Feed and Vent? if so then little or no fear of pump over/back.

nordicb

Yes, exactly same it seems. There are 2 other pipes attached to the tank, mains water feed via valve, and overflow running outside.

I tried looking on the web, but can't quite find the same picture of the water in the tank. It doesn't look like crust or slime, it's just not transparent, as if someone poured black ink into it. Slime probably was a wrong description to use. I'm going to drain the tank only and refill with deionized water I had remains of somewhere for the car.

John.G

The water stays stagnant in these tanks for years, I have an isol valve on the make up to the ball cock which I keep closed and open it a few times a year and its amazing but I have never heard a drop of water going into it between my very very infrequent drain downs, some say that open vented systems are prone to absorbing oxygen etc but some of my rads are original, installed in 1975 ish. I do put inhibitor in whenever I drain down.

nordicb

Thanks for all the input John.G. Same as you, throughout the year, the level dropped only by 1cm or so, it's just this water contamination that worries me. Just drained the tank, there were no solids or sludge, just this layer of slippery stuff on walls.

It suddenly occurred to me what the smell reminds me of - same as what you get with fish tank, algae kinda smell, so it probably is an algae.

Looks like I may need the biocide, unless someone kindly suggests something else...

John.G

A few spoonfuls of household bleach?.

nordicb

It crossed my mind, but I'm not sure how good or bad it is.
I once thought of using automotive coolant stuff, like VAG G12 or G13, which has everything cooling (or heating) system needs. But this stuff is hazardous to environment and there would be a lot of it if it ever needs draining.

John.G

I have a garden fountain for years which circulates the water for a few hours each day and I have no problem in keeping the algae at bay with a few squirts of household bleach every week or so. It certainly won't do any harm.

nordicb

Thank for suggestion, I guess there is no harm since it is such a low concentration, I may try this.