Please Note:The mini heat pump does have a water flow sensor within, so will turn off when water flow stops (E3 will show to indicate no water flow). However, the units will try to repeatedly restart after every 4 or 5 minutes to try to sense if flow has returned to the unit. If the waterflow has not returned the restarts will continue, this could lead to high wear and tear on the compressor and also E1 Errors (high refrigerant pressure). The E1 error requires a manual turn off of power to the unit completely and time to cool off allowed for the unit. Then the unit can be restarted if waterflow is present. The E3 error, does not require user intervention and will clear when water flow returns. This is not the case with the E1, so the heater is in affect off until it is manually restarted regardless of water flow. D.B Ratings - 10mtr - 39db - 1mtr - 59db Reviews. Find out what genuine customers have said about ukpoolstore.co.uk. Real product reviews from real people.">