DESC:FIELD The present disclosure relates to the field of pumping and trapping devices. DEFINITIONS Saturated vapour: The expression “saturated vapour” used hereinafter in this specification refers to a vapour whose temperature and pressure is such that any isothermal compression of its volume causes it to condense to liquid at a rate sufficient to maintain a constant pressure. For example, at 1.01325 bar (i.e., standard atmospheric pressure at sea level), steam is a saturated vapour at 100°C (373K). Modes of operation: The expression “modes of operation” used hereinafter in this specification refers to, but is not limited to, modes of operation of the pumping and trapping device which include a trapping mode, a pumping mode, and a mode in which the pumping device is not recovering any condensate. In the trapping mode, the pumping and trapping device is recovering condensate and allowing the condensate to further flow through its outlet port. In the pumping mode, the device is pumping the condensate out of its shell through its outlet port against the pressure of the condensate accumulated in the condensate outlet conduit. In the pumping mode, the device goes through a filling cycle and a pumping cycle. In the filling cycle, the device gets filled with the condensate without any flow of the condensate out of the outlet. In the pumping cycle, the device pumps the filled in condensate out of the outlet. The device can undergo, in the pumping mode, a cyclic operation between the filling and the pumping cycles. Shell Bypass: The expression “shell bypass” used hereinafter in this specification refers to a port configured on the shell of a pumping and trapping device to tap on the pressure acting on the condensate filled within the shell of the device. BACKGROUND The background information herein below relates to the present disclosure but is not necessarily prior art. A pumping and trapping device is typically connected between a heat exchanger and a storage tank, and is used to remove condensate from the heat exchanger. The pumping and trapping device typically operates in two modes, i.e., a trapping mode and a pumping mode. The pumping and trapping device operates in trapping mode when upstream pressure in the device is greater than the downstream pressure in the device. The pumping and trapping device operates in pumping mode when downstream pressure in the device is greater than the upstream pressure in the pumping and trapping device. However, it is not possible to determine whether the device is functional or is non-operative by only visually inspecting the device. Further, it is impossible to determine the mode of operation of the device, i.e., whether the device is operating in a pumping mode or a trapping mode, by visual inspection. Therefore, there is felt a need of an indicating means that identifies and indicates the mode of operation of a pumping and trapping device. OBJECTS Some of the objects of the present disclosure, which at least one embodiment satisfies, are as follows: An object of the present disclosure is to provide means for indication that identifies and indicates mode of operation of a pumping and trapping device. Another object of the present disclosure is to provide means for indication that can be easily retrofitted with existing pumping and trapping devices. Yet another object of the present disclosure is to provide means for indication that has a simple configuration. Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure. SUMMARY The present disclosure envisages means for indicating the modes of operation of a pumping and trapping device. The means is configured to detect the modes based on pressure differential between the condensate inlet and the condensate outlet and between the shell bypass and the condensate outlet of the device relative to temperatures at the shell bypass and the condensate outlet of the device. The means for indicating the modes of operation of a pumping and trapping device comprises a first piston-cylinder apparatus, a second piston-cylinder apparatus, a first temperature sensing unit and a second temperature sensing unit. The first piston-cylinder apparatus is fluidly connected between the condensate inlet and the condensate outlet of the pumping and trapping device. The first piston-cylinder apparatus comprises a first cylinder and a first piston. The second piston-cylinder apparatus comprises a second cylinder and a second piston. The first cylinder has a first port and a second port. The second cylinder has a third port and a fourth port. The first port is in fluid communication with the condensate inlet of the pumping and trapping device and the second port is in fluid communication with the condensate outlet of the pumping and trapping device. The third port is in fluid communication with the shell bypass of the pumping and trapping device and the fourth port is in fluid communication with the condensate outlet of the pumping and trapping device. The first piston is disposed within the first cylinder and second piston is disposed within the second cylinder. The first temperature sensing unit is configured to measure and indicate temperature at the shell bypass of the device. The second temperature sensing unit is configured to measure and indicate temperature at the condensate outlet of the device. Combinations of positions of the first piston relative to the first port and the second port and positions of the second piston relative to the third port and the fourth port with said temperature measurements indicated by said first and second temperature sensing units indicate the modes of operation alongwith conditions of the device. Combinations of the positions of the first and second pistons are indicative of the modes being a trapping mode comprising the conditions of working, steam leak, water log and stall, and a pumping mode comprising a filling cycle and a pumping cycle. In an embodiment, the first and second cylinders are partially transparent to allow visual inspection of positions of the first and second pistons relative to the first and second ports of the first cylinder and the third and fourth ports of the second cylinder respectively. In another embodiment, the first and second cylinders are fully transparent. In another embodiment, the piston-cylinder apparatuses comprise magnets embedded into the first and second pistons at each of the longitudinal ends thereof. Magnetic reed switches are mounted at longitudinal ends of the first and second cylinders respectively. The switches are configured to sense the positions of the magnets such that the switch closer to the magnets gets activated and thereby indicates position of the corresponding piston relative to the ports of the corresponding cylinder. In an embodiment, digital means is configured to indicate the modes of operation. The digital means includes a detecting unit and a display unit. The detecting unit is configured to detect output of the reed switch and determine the current mode of operation of the device. The display unit is in communication with the detecting unit and is configured to display the detected mode of operation. The means for indication further comprises a condensate inlet bypass conduit, a first condensate outlet bypass conduit, a shell bypass conduit and a second condensate outlet bypass conduit. The condensate inlet bypass conduit fluidly connects the first port of the first piston-cylinder apparatus with the condensate inlet of the device. The first condensate outlet bypass conduit fluidly connects the second port of the first piston-cylinder apparatus with the condensate outlet of the device. The shell bypass conduit fluidly connects the third port of the second piston-cylinder apparatus with the shell bypass of the device. The second condensate outlet bypass conduit fluidly connects the fourth port of the second piston-cylinder apparatus with the condensate outlet of the device. In an embodiment, the vapour is steam. The present disclosure also envisages a method for indicating the modes of operation of a pumping and trapping device. The method comprises: i. providing a first cylinder having a first port and a second port at longitudinal ends thereof and a first piston displaceable between the first port and the second port; ii. providing a second cylinder having a third port and a fourth port at longitudinal ends thereof and a second piston configured to be displaceable between the third port and the fourth port; iii. connecting the first port of the first cylinder with the condensate inlet of the device, the second port of the first cylinder with the condensate outlet of the device, connecting the third port of the second cylinder with the shell bypass of the device and connecting the fourth port of the second cylinder with the condensate outlet of the device; and iv. identifying position of the first piston relative to the first port and the second port and position of the second piston relative to the third port and the fourth port; v. providing a first temperature sensing unit at the shell bypass and providing a second temperature sensing unit at the condensate outlet; vi. reading a first temperature measured and indicated by the first temperature sensing unit and reading a second temperature measured and indicated by the second temperature sensing unit; vii. comparing the first temperature with a first predetermined temperature and the second temperature with a second predetermined temperature; viii. determining a mode of operation and an associated condition of the device based on the following relations: a) when the first piston is proximal to the second port, the second piston is proximal to the fourth port, temperature measured and indicated by the first temperature sensing unit is greater than a predetermined temperature and temperature measured and indicated by the second temperature sensing unit is less than a predetermined temperature, the device is in trapping mode and working normally; b) when the first piston is proximal to the second port, the second piston is proximal to the fourth port, temperature measured and indicated by the first temperature sensing unit is greater than a predetermined temperature and temperature measured and indicated by the second temperature sensing unit is greater than a predetermined temperature, the device is in trapping mode and is leaking steam; c) when the first piston is proximal to the second port, the second piston is proximal to the fourth port, temperature measured and indicated by the first temperature sensing unit is less than a predetermined temperature, the device is in trapping mode and is logged with water; d) when the first piston is proximal to the second port, the second piston is proximal to the third port, temperature measured and indicated by the first temperature sensing unit is less than a predetermined temperature, the device is in trapping mode and is stalled; e) when the first piston is proximal to the first port, the second piston is proximal to the third port, irrespective of temperatures indicated by the first temperature sensing unit and the second temperature sensing unit, the device is in pumping mode with a filling cycle ON; f) when the first piston is proximal to the first port, the second piston is proximal to the third port, irrespective of temperatures indicated by the first temperature sensing unit and the second temperature sensing unit, the device is in pumping mode with a pumping cycle ON; and g) when the first piston is proximal to the first port, the second piston is continuously reversing position between the third port and the fourth port, irrespective of temperatures indicated by the first temperature sensing unit and the second temperature sensing unit, the device is cyclically switching between the pumping and the trapping modes of operation. The first predetermined temperature and the second predetermined temperature are temperatures of saturated vapour corresponding to the pressure at the shell bypass and at the condensate outlet respectively of the pumping and trapping device. BRIEF DESCRIPTION OF ACCOMPANYING DRAWING Means for indicating the modes of operation of a pumping and trapping device of the present disclosure will now be described with the help of the accompanying drawing, in which: Figure 1 illustrates a heat exchanger with a pumping and trapping device; Figure 2 illustrates a block diagram depicting a pumping and trapping device with means for indicating the modes of operation of a pumping and trapping device according to an embodiment of the present disclosure; Figure 3 illustrates a sectional view of a first cylinder of the means for indicating the modes of operation of a pumping and trapping device according to an embodiment of the present disclosure; Figure 4 illustrates a sectional view of a second cylinder of the means for indicating the modes of operation of a pumping and trapping device of the present disclosure; Figure 5 illustrates a sectional view of a first cylinder of the means for indicating the modes of operation of a pumping and trapping device according to another embodiment of the present disclosure; Figure 6 illustrates a sectional view of a first cylinder of the means for indicating the modes of operation of a pumping and trapping device according to another embodiment of the present disclosure. LIST OF REFERENCE NUMERALS 5 heat exchanger 10 reservoir 12 cold water inlet 14 hot water outlet 16 steam inlet conduit 18 steam exhaust conduit 20 steam control valve 22 temperature controller 24 steam temperature sensing unit 50 pumping and trapping device 52 float 54 high-pressure steam valve 55 inlet check valve 56 condensate inlet 57 shell bypass 58 condensate outlet 65 condensate inlet conduit 60 outlet check valve 70 condensate outlet conduit 75 motive steam exhaust conduit 80 motive steam inlet conduit 125 condensate inlet bypass conduit 130 first condensate outlet bypass conduit 135 shell bypass conduit 140 second condensate outlet bypass conduit 200 first piston-cylinder apparatus 205 first cylinder 210 first port of first cylinder 215 second port of first cylinder 220 piston of first cylinder 225 sealing element of first cylinder 230 stopper of first cylinder 235 magnet 300 second piston-cylinder apparatus 305 second cylinder 310 first port of second cylinder 315 second port of second cylinder 320 piston of second cylinder 325 sealing element of second cylinder 330 stopper of second cylinder 335 magnet 410 first temperature sensing unit 420 second temperature sensing unit DETAILED DESCRIPTION Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing. Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail. The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms “comprises”, “comprising”, “including” and “having” are open-ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed. When an element is referred to as being “mounted on”, “engaged to”, “connected to” or ‘coupled to” another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed elements. The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure. Terms such as “inner”, “outer”, “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures. A heat exchanger for heating cold water using steam is usually equipped with a steam trap, through which the condensate formed in the heat exchanger is discharged into the condensate outlet conduit. When demand for hot water drops, steam pressure in the heat exchanger which is controlled by a control valve also drops. If the steam pressure in the heat exchanger drops below the pressure in the condensate outlet conduit, the condensate starts to back up into the heat exchanger’s steam channels, the situation termed as ‘stall’, which results in unstable temperature control by the temperature controller 22 and effects such as water hammer. As illustrated in Figure 1, the steam trap of prior art is replaced with a pumping and trapping device 50, which is configured to operate as a pump, i.e., to pump the condensate collected within the shell thereof into the condensate outlet conduit 70. The device 50 operates in pumping mode when the pressure in the condensate inlet conduit 65 drops below the pressure in the condensate outlet conduit 70, in case of drop in demand of hot water from the heat exchanger 5 below a threshold level. As the level of the condensate rises in the shell of the device 50, the float 52 is lifted up. After reaching a certain level, a mechanism linked with the float 52 actuates the high pressure steam valve 54. Through the valve 54, the pressurized steam through the motive steam inlet conduit 80 pumps the condensate back into the condensate outlet conduit 70, until the valve 54 closes back again. An operator is however unable to determine from the outside as to what mode, out of trapping mode or pumping mode the pumping and trapping device 50 is operating in, or whether the ‘stall’ has occurred in the system. There is a need for means for indication which identifies and indicates mode of operation of a pumping and trapping device 50. The present disclosure envisages means for indicating the modes of operation of a pumping and trapping device 50 based on pressure differential between the condensate inlet 56 and the condensate outlet 58 and between the shell bypass 57 and the condensate outlet 58 of the pumping and trapping device 50 relative to temperatures at the shell bypass 57 and the condensate outlet 58 of the device 50. Figure 2 illustrates a schematic block diagram of a pumping and trapping device 50, wherein the device 50 is configured to receive condensate through condensate inlet conduit 65 through an inlet check valve 55 and discharge the same to a condensate outlet conduit 70 through an outlet check valve 60. The device 50 receives motive steam through a motive steam inlet conduit 80 and discharges the steam through a motive steam exhaust conduit 75. According to an embodiment of the present disclosure, means for indication including a first piston-cylinder arrangement 200, comprising a first cylinder 205 and a first piston 220, and a second piston-cylinder arrangement 300, comprising a second cylinder 305 and a second piston 320, is configured to indicate operational mode of the device 50. The first cylinder 205 is connected between the condensate inlet 56 and the condensate outlet 58 of the device 50, while the second cylinder 305 is connected between the shell bypass 57 and the condensate outlet 58 of the device 50. The first cylinder 205 houses the first piston 220 and the second cylinder 305 houses a second piston 320. The pistons are configured to be slid in the respective cylinders based on the pressure differential across the cylinders. Further, one temperature sensing unit each is inserted at the condensate inlet and the shell bypass of the pumping and trapping device 50, as illustrated in Figure 1. The temperature T1 is measured by the first temperature sensing unit 410 at the condensate inlet and the temperature T2 is measured by the second temperature sensing unit 420 at the shell bypass. T1 is compared with T1set and T2 is compared with T2set, wherein T1set and T2set are pre-determined temperatures based on the operating conditions of the pumping and trapping device 50. These temperatures are co-related from the temperature of saturated steam corresponding to upstream pressure (P1) and downstream pressure (P2) respectively (e.g., temperature of saturated steam at atmospheric pressure 1.01325 bar is 100°C). In an embodiment, the temperature sensing units 410, 420 are temperature sensors. The combinations of the positions of the pistons 220, 320 within the respective cylinders 205, 305 with the temperatures detected by the temperature sensing units 410, 420 indicates modes of operation of the device 50. As illustrated in Figure 3, the first cylinder 205 has a first port 210 and a second port 215. The first port 210 is in fluid communication with the condensate inlet conduit 65. In an embodiment, the first port 210 is connected to the condensate inlet conduit 65 via a condensate inlet bypass conduit 125. The second port 215 is in fluid communication with the condensate outlet conduit 70. In an embodiment, the second port 215 is connected to the condensate outlet conduit 70 via a first condensate outlet bypass conduit 130. Further, as illustrated in Figure 4, the second cylinder 305 has a third port 310 and a fourth port 315. The third port 310 is in fluid communication with the device 50. In an embodiment, the third port 310 is connected to an inner portion of the device 50 via a shell bypass conduit 135. The fourth port 315 is in fluid communication with the condensate outlet conduit 70 via a second condensate outlet bypass conduit 140. The first cylinder 205 of the first piston-cylinder apparatus 200 has a hollow cylindrical configuration. The first port 210 and the second port 215 are configured on longitudinal ends of the cylinder 205. Further, the first piston 220 is disposed within the first cylinder 205 between the first port 210 and the second port 215. The first piston 220 is freely movable within the bore of the first cylinder 205. Further, a sealing element 230 is disposed between the first piston 220 and the bore of the first cylinder 205 to prevent leakage of condensate across the first piston 220. The first cylinder 205 further comprises two stoppers 230. One of the two stoppers 230 is disposed between the first piston 220 and the first port 210, and the other stopper 230 is disposed between the first piston 220 and the second port 215. The second piston-cylinder apparatus 300 comprises a second cylinder 305, a second piston 320, a sealing element 325 and two stoppers 330. The configuration of the second cylinder 305 is same as that of the first cylinder 205. Thus, the configuration of the second piston-cylinder 300 is not described here again for the sake of brevity of the disclosure. The stoppers 230, 330 are configured to prevent the pistons 220, 320 from colliding with the ports 210, 215 and the ports 310, 315 respectively. In an embodiment, a portion of each of the first cylinder 205 and the second cylinder 305 respectively is made transparent to facilitate visual inspection of the movement of the first piston 220 and the second piston 320 respectively by an operator. In another embodiment, the first cylinder 205 and the second cylinder 305 respectively are made entirely transparent for facilitating visual inspection of the pistons 220, 320. In yet another embodiment, as illustrated in Figures 5 and 6, magnets 235, 335 are embedded on the longitudinal ends of the first piston 220 and the second piston 320 respectively. Magnetic reed switches (or any other suitable sensing arrangement) (not illustrated in Figures) are configured to sense the positions of the magnets 235, 335 by mounting on longitudinal end of the first cylinder 205 and the second cylinder 305 respectively. The switch that is closer to the magnets gets activated and thereby indicates position of the corresponding piston. In an embodiment, the switches associated with the positions of the pistons are part of a circuit (not illustrated in Figures) which selectively turns on indicator elements such as light-emitting diodes (LEDs) based on the combination of position of the first piston 220 and the second piston 320 detected. The circuit comprises four LEDs corresponding to the four combinations of positions. In another embodiment, indication of the mode of operation is provided via digital means. The digital means includes a detecting unit and a display unit. The detecting unit is configured to detect output of the reed switch by using any suitable means and determine the current mode of operation of the device 50. The detecting means is in communication with the display unit, which displays the detected mode of operation. a. Trapping mode: The first piston 220 disposed within the first cylinder 205 is detected proximal to the second port 215 when the trapping cycle of the pumping and trapping device 50 is trapping mode. While the first piston 220 is near the port 215, the following observations on the second cylinder 305 and the temperatures T1 and T2 sensed by the first and the second temperature sensing units 410, 420 are made. While the second piston 320 is near the fourth port 315, T1 is higher than T1set and T2 is lower than T2set, the device 50 is working normally as a trap. However, while the second piston 320 is near the fourth port 315, T1 is higher than T1set and T2 is also higher than T2set, steam leak in the device 50 is detected. While the second piston 320 is near the fourth port 315 and T1 is lower than T1set, water logging in the device 50 is detected. On the other hand, while the second piston 320 is near the third port 310 and T1 is lower than T1set, stalling of the device 50 is detected. Any observations of the temperature T2 sensed by the second temperature sensing unit 420 are redundant, when the temperature T1 is lower than T1set. b. Pumping mode: The first piston 220 disposed within the first cylinder 205 is detected proximal to the second port 215 when the pumping and trapping device 50 is in pumping mode. While the first piston 220 is near the first port 210, and the second piston 320 is near the third port 310, the filling cycle of the device 50 is on. On the other hand, while the first piston 220 is near the first port 210, and the second piston 320 is near the fourth port 315, the pumping cycle of the device 50 is on. Any observations of the temperatures T1 and T2 sensed by the first and the second temperature sensing units 410, 420 are redundant, when the device 50 is detected to be in pumping mode by detecting the first piston 220 near the first port 210. For determining functionality in the pumping mode, the continuous reversal of slider positions in cylinder 305 needs to be checked, since it indicates that the device 50 is alternating between the pumping and filling cycles. The combinations of positions of the pistons 220, 320 combined with the temperature measurements T1 and T2 using the temperature sensing units 410, 420 and the corresponding inferences are summarized in Table 1 below. Table 1: Sr. no. Mode of operation of Device 50 Condition/ functionality Position of First Piston 220 (A=near first port 210/ B=near second port 215) Position of Second Piston 320 (C=near third port 310/ D=near fourth port 315) T1 T2 1 Trapping working B D T1>T1set T2T1set T2>T2set 3 Trapping water log B D T1