HELP...... Totally stumped. Water was dripping from F & E tank overflow . F & E tank is below the level of the cw tank in the loft. Took all rads off walls & flushed them through with a power washer in the garden. Refitted rads and put Fernox SD40 into the F & E tank and ran the system for a few days before draining and putting the neutraliser in the F & E tank. Ran the system for a few hours and then drained / refilled system 4 or 5 times to flush out all sludge / sediment. Pipework now clear ( magnet not sticking to any of them ) Water level in the F & E tank still rose & overflow was still dripping so replaced the HW tank yesterday as all symptoms suggested that the coil may have been burst. Got up this morning to the sound of dripping water from the F & E overflow ... Turned the heating & hw off & drained down the water in the F & E tank and noted the level in tank. Just been up in the loft for a nosey and the water level in the F & E tank has risen 1.5" over the last 3 hours with the inlet valve closed and the ballcock tied up. Water is definitely coming back up the heating supply pipe into the F & E tank. Any idea on where this water is coming from ? What should I do next ?