If the pressure in the vessel is too high, you must clean the filter bed (sand in the boiler) by backwashing.
When using filter balls, check them regularly for soiling, remove them from the vessel at regular intervals and sluice them out. Clean the filter balls with a garden hose or in the bathtub.
DO NOT BACKWASH WHEN USING FILTERBALLS!
If the pressure in the vessel is too low, you must check and clean the pre-filter for dirt so that sufficient water can flow into the pump.
Check the water level and the height of the surface skimmer, if the water level is too low, too little water flows into the pump.
Check the manometer for damage.