hot water in expansion tank

i have a boilermate 2 and it has hot water coming from the expansion pipe on the right causing the expansion tank to overflow
when i run the hot water taps the level in the expansion pipe goes down but as soon as the taps are stopped it comes up and into expansion tank but only 100ml of water , the water that comes up is clear
is this an issue of sludge or the internal coil leaking

if it is sludge is there any way i could clean it myself

If it was the coil then it would keep on filling the F&E tank as the coil is mains water pressure.
You could try draining the unit.
Removing F&E tank.
Check that the cold feed and vent are clear on the unit.
Mike
MGC/H2O
Norfolk

i drained some out from bottom of cylinder and brown liquid came out then went clear so stopped this seemed to stop it but when i ran a bath and went to check it started to drip out of the expansion pipe once i guess the cylinder refilled to top

thanks for reply mike

It would pay to drain complete.
And check what I told you.
Mike