If your stand steamer is steaming weakly, then it needs to be descaled.
To solve this, please descale it as follows:
1) Switch off and unplug your stand steamer. Allow it to cool down for an hour.
2) Bring the steamer to a sink.
3) Locate the de-calc knob (you will find it on the lower area of the water tank).
4) Turn the de-calc knob anti-clockwise to unlock it.
5) Pull the de-calc knob out and let the water drain.
6) Once all water is drained, push the de-calc knob back in and turn it clockwise to lock it.