English 5.906-432.0 Rev. 00 (06/15) 45The lack of water fuse prevents the burner from switchingon in case of missing or insufficient water volume and thusprotects the on-demand heater from overheating.With an opened gun and a sufficient water flow the sole-noid is lifted against the force of gravity in the cartridge.The solenoid piston closes the contact of the reed switch.This opens the fuel solenoid valve and the burner ignites.The sieve in the water supply of the safety block preventsthe contamination of the lack of water fuse.The lack of water fuse is a safety component and thereforeits locking screw is sealed.The information regarding insufficient water volumes issent directly to the control PCB.There, this message is evaluated as– lack of water fuse (shut-off of burner, see above) and as– Dry-run protection for the pump (switch-off device).The lack of water fuse functions immediately.It switches the burner off immediately in case of insufficientwater volume and back on after the water level has beenreplenished.The dry run protection is intitiated when the lack of waterfuse signals insufficient water volume for 2 minutes.The appliance shuts off with a fault message and locks up.Only by switching the device off and back on via the mainswitch, it can be taken into operation again.As the dry-run protection damages the pump in the longrun, there must always be a sufficient water supply.The safety valve guides the entire flow rate of the pump tothe float container if the pressure switch or the overflowvalve is defective and thus protects the device and acces-sories from inadmissibly high overpressure.If the gun is open, the safety valve is closed and the entireflow volume of the pump is transferred to the gun at oper-ating pressure.If the pressure in the high pressure system rises by ap-prox. 20 bar above the permissible operating pressure, thevalve ball is lifted off the valve seat and part of the flow vol-ume flows into the swimmer reservoir.The opening pressure of the safety valve is adjusted withthe adjustment screw.Rotation to the right increases the opening pressure, rota-tion to the left decreases the opening pressure.The safety valve is a safety component and therefore itsadjustment screw is sealed.NoteThe safety valve is adjusted via the pressure increase inthe system with the burner turned on, so that it limits thepressure increase to the max. permissible value (seeSpecifciations) with the gun closed.Then seal the settings.6.19.3 Function water shortage safeguard and dry-run protection6.19.4 Function of safety valve
