Vented thermal store mould fil expansion

[seanff]

Hi,

I have tried fought with this issue for nearly a year.

When I moved in, the full and expansion tank was clear.

I had a issue with the immersion heaters so they needed replaced, I replaced them myself with the recommended upgrade kit (Eldon coral e 150l.). I drained the tank, replaced and refilled via the fill and expansion using along with fernox F1.

Since then I have several issues with mould in the full and expansion tank. I have emptied the fill and expansion tank three times now. First i drained the full system again, I noticed on the water in the f+e was mouldy (jellyish), the main tank came out clear. When refilling I added fernox F1 and f8(biocide) l The second time I gave the f+e tank a good dose of bleach and scrubbed everything in the tank left it standing, before rinsing and refilling ( just the f+e tank. However the mould came back (grey/beige masses). The third time the mould came back quicker and is more green spores on the surface with jelly underneath, again I gave this a very good scrub and taped up a unused hole in the f+e tank incase light and air was getting in. I added two bottles of plumb centre inhibitor and sentinal x700(? Biocide) , this is added without draining the main tank again. However the mould has returned and I'm sick of it. Ive read I can add some bleach to the f+e without rinsing it out but I guess it's going to end up the same.

Does anyone have any experience or suggestions? Draining the full storage tanks ages as I have to use a bucket. It is also starting to become expensive buying the chemicals.

 

[Johntheo5]

Is the bottom of the CWS cistern higher or lower than the bottom of the Feed&Expansion cistern and is the CWS cistern water level higher or lower than the water level in the F&E cistern??.

 

[seanff]

By CWS, is that cold water storage? The thermal storage is lower, as it evaporates it enters the F+E and the colder water from the F+E feeds back into the thermal store. Hot water is isolated and cold water is ran through the heat exchanger coils which make contact with the thermal stores hot water. Here is a picture that better descries the setup, the top right is the F+E where the mould is. Mine is a manual fill without the float.

 

[Johntheo5]

That looks like a Vented thermal store?.
Is it only heated by the electric immersion(s)?.
Is the DHW just forced through the coils from the mains to heat it?, if so, there may be a pin hole in the coil causing contamination of the store water but you then should see the F&E cistern overflowing continuously, even if only a small amount.

 

[seanff]

Apologies, it is vented!

 

[Johntheo5]

OK, so, is it heated only by the electric Immersions or is it also directly heated by a gas/oil fired boiler?

 

[seanff]

only by electric immersions. bottom is offpeak , top is boosted, both get used depending on schedule, they should stop heating at a limit (70 degrees AFAIK).

I've decided to empty it (red cap is to prevent stuff entering the thermal store), poured domestic bleach and gave a scrub (again), im tempted to rinse it , top up and add some bleach to the F+E tank.

 

[Johntheo5]

Ensure there is enough of a air gap when cold to ensure it doesn't overflow each time it heats up especially if the bottom, off peak element has been used, look into the F&E cistern just after reheating, very little, or practically no make up should be required normally via the ballcock.