warm water coming from cold tap in bathroom

I'm getter more and more confused by the advice in this thread.

None of what has been suggested will have an affect on the domestic water which is brown.

The only way this can happen is if, the heating has been connected to the hot pipe, but then that wont apply for the cold unless thats been connected as well.

As far as I'm concerned the cylinder coil must be split, or the water board has been working on the mains, but that don't answer why the kitchen is clear, unless the kitchen is mains fed and the hot is from another source e.g. combi.

Now I'm more confused

I would not add inhibitors or chemicals into the heating untill the hot water problem is resolved.

Ah yes.... I had been wondering last night if the vent from the top of the cylinder might have been bent down over the CH F&E and sucking in dirty water, e.g. from a power shower, but forgot about that today. I could not see why else rusty water would get into the taps,

Benny had said that the F&E tank is lower than the cold Cistern, so I skipped over the possibility of a split coil.

I was thinking he would come back if the trouble remained.

An old galvanised cylinder, tank or pipework would have been the obvious answer.

But he don't have none

Another possible answer would be if some numskull has connected a radiator or steel towel rail to a secondary circuit.

After reading through texts still not sure which vent was below water level,If its the large F/E cistern the brown water may not be rust but the brown sludge deposits u get from water mains over a long time. 30 year old cylinders can have a 1/2" layer of soil deposits just waiting to be disturbed, If the dhw vent is below the water level that would cause a thermal syphon up the vent & down the cold feed. that would explain the warm low pressure cold water & it may of dislodged & circulated the dirt in the bottom of the cylinder as the cylinder will become hot completly top to bottom.

could the old immersion be a factor - rusting away?