Initially, for milk frothing issues, soak the milk jug cover in hot water and rinse several times. If it has a froth control that can be removed by sliding in the direction of travel towards the edge whilst jiggling it gently up and down. Clean off the little o-ring with a toothpick, be gentle. Muck out the inside of the lid. The control should easily slide and click back in place when done.
Froth still no good? Examine the milk coupling to ensure the o-rings are in the right spot and are pliable and undamaged. There should be an o-ring (usually green) on the top spigot, a (black) o-ring at the front of the bottom spigot and a (red) oring at the rear. The groove halfway along the spigot should be clear. Now with the toothpick and a hot moist cloth clean all the crud from the milk coupling, especially inside the smaller spigot. Check the tiny hole at the back of the larger spigot is not blocked.
Check the flow from the hot water spout is good. If not, there are internal issues, try descaling. If it is, test the frothing jug, if it is still weak either the jug cover or the milk coupling needs to be replaced. Get them to try a known good test jug at your local coffee service center to find out which, most will be happy to do this at the counter.
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