F&E tank overflow - brownish water - tap water crystal clear

[helon]

Have traditional vented indirect system, in my case F&E tank base same level as large tank, so top level of f&e tank is lower, F&E tank overflows/steady trickle, maybe one bucket every 3 hours, also somewhat brownish water (water from taps crystal clear), guess it is coil, or could system be too hot (at one stage hot water was VERY hot), any suggestion?

 

[SavageW]

Sounds more like the vent on the f&e tank is pumping over, whenever I’ve come across split cylinder coils you get iron oxide particles coming out your hot water taps/discoloured water. Could be your hw zone valve microswitch sticking causing the boiler an pump to be on with nowhere to circulate then ending up pumping over via the open vent & slightly passing through the hw zone valve to heat the coil giving you hotter water. It’s just a guess mate given you said hot water was very hot, H section could also be restricted causing f&e tank to overfill.

 

[helon]

Sounds more like the vent on the f&e tank is pumping over, whenever I’ve come across split cylinder coils you get iron oxide particles coming out your hot water taps/discoloured water. Could be your hw zone valve microswitch sticking causing the boiler an pump to be on with nowhere to circulate then ending up pumping over via the open vent & slightly passing through the hw zone valve to heat the coil giving you hotter water. It’s just a guess mate given you said hot water was very hot, H section could also be restricted causing f&e tank to overfill.

Thanks, very detailed, pity you are not a plumber in my area (N20), even as a lay person I would have thought that if there is a hole in the coil it lets water from heating circuit into the cylinder and then tap water is discolored (Though somewhere I read it could be the other way, depending on relative positions of small and large tank, but somehow cannot imagine water FROM cylinder goes into heating circuit, would at some stage be overfull, though maybe that is why overflow goes into f&e tank).
Also worth mentioning, water goes into f&e tank not from the vent pipe hanging over the edge and freely visible, it must come from the opening at the bottom level...any more ideas? drives me mad, worse than the Rubik cube!

 

[Gasmk1]

sound like a job for plumber heating engineer.