fig1 and 2 depict the structure and circuitry , respectively , of the present invention . the houshold coffee machine of this invention includes a flow heater 2 , a cold water supply conduit 7 , and a hot water outflow 8 . a thermostat 4 controls the temperature of the flow heater 2 . a heat responsive switch 5 controls operability of a calcification indicator 6 . the calcification indicator device 6 is series connected with its thermally responsive switch 5 . device 6 and switch 5 are connected in parallel with the thermostat 4 . further , the heat detector means of the switch 5 is mounted at the cold water supply line 7 so as to be thermally responsive to cold water line temperatures . the aforesaid household coffee machine is further characterized in that the calcification indicator circuit ( i . e . the circuit including 5 , 6 ) is designed with relatively high - impedance , as compared to the resistance of the thermostat 4 . in the household coffee machine as above noted , the thermostat 4 and the heat detector of the switch 5 are so adjusted that , where excessive calcification of the flow heater 2 exists , the thermostat 4 will be opened because of the temperature rise in the flow heater 2 , while the heat responsive switch 5 remains closed because of the temperature of the cold water in the cold water supply line 7 . the cut - in or switch opening temperature , at which ( and below which ) the switch 5 keeps the calcification indicator device in operable state , lies below the switch opening temperature of thermostat 4 . thus , the cut - out temperature and the opening temperature of the thermostat 4 and of the thermally responsive switch 5 respectively are so coordinated that when flow heater 2 is not excessively calcined and overheated , the switch 5 is opened after conclusion of the water heating process and before the switch of the thermostat 4 opens , each opening occurring in response to the presence of steam in line 7 as hereinafter described . thus , the thermostat 4 may be characterized by a &# 34 ; cut - out &# 34 ; or switch opening temperature that is at least 40 ° c . higher than the desired operating temperature of unit 2 , while switch 5 may be characterized by a switch opening temperature that is only about 30 ° c . higher than the desired fresh water temperature . as shown in fig2 a manually operable turn - on / turn - off switch 1 is included in the preferably grounded circuit . fig1 depicts a household coffee machine which is provided with a plate - shaped flow heater 2 . flow heater 2 has an internal water flow passage which serves to heat water . heater 2 also acts as a hot plate for heating the coffee jug 17 which , after coffee making is concluded , is set down on the top of the plate - shaped flow heater . the &# 34 ; holding &# 34 ; or pot heating temperature of the flow heater 2 is kept constant with switching thermostat 4 . a thermal fuse 3 , is series connected with the thermostat ( heat level responsive switch ) 4 and the filament winding of the flow heater 2 . this fuse is temperature responsive and protects the appliance in case the thermostat fails . the switch opening temperature of the thermostat 4 is so selected that during the water heating process , there occurs no opening of the circuit in unit 4 , unless excessive calcification should be present on the interior , flow passage , walls of flow heater 2 . when making coffee , water flows from a fresh water container 9 through the cold water line 7 , via a check valve 10 , to the cold water inlet 12 of the flow heater 2 . in the flow heater 2 , the water is heated and flows through a flow heater outlet 13 to the hot water line 8 , through the standpipe 14 , through the water overflow 15 , through the coffee - filled filter 16 and into the coffee jug 17 . after prolonged use and depending on the lime content of the applied water , the water passage of the flow heater 2 becomes calcified , especially in the region of the hot water outlet 13 and the portion of line 8 near this outlet . upon the beginning of calcification , there occurs a substantial decrease in heat conductance in unit 2 so that unit 2 overheats and the thermostat 4 opens its switch during the water heating process . the supply of current to the heating filament of the flow heater is now supplied through elements 5 and 6 until the completion of water heating . because of the good heat - conducting connection of the thermal actuator sensor of switch 5 with the cold water line 7 , the switch contact of the heat detector 5 ( switch 5 being of a thermostat type ) remains closed during water heating so that the current now flows through the heat detector 5 and the calcification indicator device 6 . the calcification indicator device can be a buzzer , a filament lamp or a glow lamp or the like . the calcification indicator device is thus actuated by opening of thermostat 4 and indicates to the user during the water heating process that a decalcification of the appliance is required . the opening temperature of the switch 5 which is equipped with a heat detector lies about 30 ° c . above the fresh water temperature so that the contact of switch 5 remains closed during the water heating , i . e . coffee process . as soon as the coffee making is concluded , the water boils off in the flow heater 2 and steam is generated which simultaneously escapes through the cold water inlet 12 and the hot water outlet 13 . the steam causes a temperature rise in the line 7 and thus at the heat detector location of switch 5 . this temperature rise opens the contact of switch 5 and thus shuts off heater 2 . thereafter , with the coffee filled jug 17 resting on plate 2 , heating control is maintained by thermostat 4 . the &# 34 ; hot plate &# 34 ; temperature of unit 2 , with no water in line 7 , will cause switch 5 to remain open , with pot heating being regulated by thermostat 4 . having described the &# 34 ; calcified &# 34 ; mode of operation of the invention , reference will now be made to the &# 34 ; uncalcified &# 34 ; mode of operation . as noted , the opening temperature of the switch 5 which is equipped with a heat detector which opens switch 5 at about 30 ° c . above the fresh water temperature in line 7 so that the contact of switch 5 remains closed during the coffee making process . to ensure that the indication device 6 is not also actuated in the &# 34 ; uncalcified &# 34 ; mode during and immediately after termination of the water flow , the switch 5 , controlling operation of the calcification indication device , is connected in heat - conductance ( i . e . cooling relation ) with the cold water line 7 . during uncalcified operations , the switch in unit 4 remains closed and the high impedance of circuit 5 - 6 prevents operation of indicator 6 . as soon as coffee making is concluded , the water boils off in the flow heater 2 and steam is generated which simultaneously escapes through the cold water inlet 12 and the hot water outlet 13 . the steam causes a temperature rise in the line 7 and thus at the heat detector of switch 5 . this temperature rise opens the contacts of switch 5 before the thermostat 4 interrupts the filament circuit . thus , the calcification indicator device is unable to operate at this point in time . this state is also maintained when the coffee jug 17 , resting on the flow heater plate 2 , is subsequently kept hot because the closing temperature of the heat - detector - equipped switch 5 lies below the ambient temperature arising during the pot holding and heat maintenance period and the cooling effect of line 7 is absent . this ambient temperature is kept approximately constant by the periodically occurring reheating of the flow heater 2 through operation of thermostat 4 . to insure that the calcification indicator device 6 does not respond during coffee making when the appliance is not calcified , that is when the contact of the thermostat 4 as well as the heat - detector - equipped switch 5 are closed , the parallel circuit to thermostat 4 is of high - impedance character . this can be accomplished , for example , through the use of a calcification indicator device of high - impedance . as will be appreciated , while individual components of the coffee maker described above may be obtained in the form of well known electrical or structural componants , the arrangement described is unique . the major advantages of the invention resides in the attainment of a calcification indicator which will not provide a false calcification indication during the water flow cycle , during the steam generating cycle at the end of water flow , or during the pot warming or &# 34 ; holding &# 34 ; cycle . however , a reliable calcification indication will be provided during the coffee making process when excessive heating of unit 2 occurs ( i . e . when calcification prevents water flow from maintaining normal water heating temperatures of unit 2 through cooling action ). the invention is not limited to the represented exemplified embodiments , but can be modified within the framework of the patent claims . thus , those skilled in this art and familiar with the present disclosure will recognize additions , deletions , substitutions , equivelant arrangements , and other modifications falling within the scope of the invention as set forth in the appended claims .
a household coffee machine of the type including a thermostatically controlled electric flow heater coupled to cold water supply and having a hot water outflow is provided with a calcification indicator connected electrically in parallel with the heater thermostat . the calcification indicator includes an indicator , such as a buzzer or glow lamp , in series with a thermal cut - out switch which is disposed in thermally responsive association with the line coupling the cold water supply to the flow heater . the series connected thermal cut - out switch and indicator have a high impedance in order to insure that the calcification indicator does not respond when the heater thermostat is closed .