Recently installed leviton combination switch was working correctly. Now when power is being drawn by the hot water tank it controls the pilot light goes out. Any suggestions or is the switch faulty? Thanks

Sounds like you have a hydro-generator on this unit. Check the output on the hydro-generator it should be about 1.5V DC. If not clean the inlet screen and check your water pressure. Water pressure less than 30 PSI will cause issues. If you have 1.2V-1.5V DC make sure the power switch is on. If the power switch is on replace the control unit. I sell parts for Bosch units only!

Do you have combination switch outlet?
Copy following link:
http://waterheatertimer.org/How-to-wire-combination-switch-outlet.html

Add comment with more information as needed.
Gene
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Not sure how it is wired now:
Following link shows how to wire combo device to operate light and outlet at same time.
http://waterheatertimer.org/How-to-wire-Cooper-277-pilot-light-switch.html#switch-outlet

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

If I understand correctly, the pilot light is not staying lit.
You light the pilot and water in the tank reaches temperature.
Once hot water is gone, then pilot light has to be lit again.

Gas pressure is good, and gas is flowing.
Thermostat is working at high end because it cuts off heating.
Vent is working because tank heats up.
Air intake is working.

Gas control thermostat might not be reading low temperature. Replace gas control valve.
Pilot tube might be dirty. Clean burner parts and combustion chamber, and air intake, and vent.
Backdraft might be blowing out pilot. Check for constant updraft by running water heater 5 minutes, and then light match under vent hood and see if smoke goes up.
Very hot air can put out pilot, especially when water heater located in attic. Add ventilation.
Improper vent might have water dripping back down into combustion chamber and putting out pilot light and rusting out the parts. Inspect for rusted parts and water.
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf

easy one first: ground wire to green screw. We have to assume the two black wires are the hot(coming from power source) and switch leg(going to light). Switch will have two brass colored screws. Looking at the switch with the off/on markings right side up. Put hot wire on upper screw and switch leg on other brass screw, With nothing hooked up, the hot wire will be the only wire with voltage on it. You can buy a non-contact voltage tester at Lowes or any place that sells electrical supplies. Now we must assume the two white wires are neutrals(one coming from power source and one going to light. The pilot light part of the switch will either have a silver colored screw or a white pigtail on it. all whites hook together. The pilot light is wired internally to the switch leg. Your switch should work properly now.

For this combo , the white wires connect to the two silver screws on one side of the combo .The black power wire connects to the screw next to the switch. IF you want to have the receptacle hot all the time then jumper the hot black from the switch screw to the receptacle screw. The screw in the center is for the black wire from any lihghts that you want to control. IF it is the receptacle that you wish to control with this switch .. then the power connects to the screw next to the switch and the center screw jump a wire to the screw next to the receptacle

This is a single pole light switch and should be wired as any other SP switch. The only difference is that is has a pilot light. All the white neutral wires are tied together and then pushed back in the box with none connected to the switch. The grounds are tied together with a jumper wire connected to the green screw on the switch. That will leave you with 2 or more black wires. If you have just two normally you can connect them to the two screws on the switch and it does not matter which screws. However it may be that with the pilot light you need to connect the wire going to the light to the top screw and the power wire to the bottom or vice versa. Try both ways. If you have more than 2 black wires you need to connect the incoming power black wire and outgoing power black wires together and then jump to one of the screws on the switch. The black wire left over is the black wire going to the light itself. If none of this works then it is obvious the pilot light in the switch is burnt out.

You cannot replace the switch with a switch/receptacle combo because there is no neutral wire. The black and white that you see are both used as hot wires. One is the Line and the other is the Load.

You have to install another 2 wire cable or replace the existing with a 3-wire cable. A 3-wire cable has a black, red, and white, plus the bare ground wire

The neon lamp inside of the switch draws very little current (milli, or mico amps) so there is no significant current flowing to ground.

As for your real question, there are several various types of 3-way pilot switches:
Load on: Pilot on
Load off: Pilot on
Some 3-way pilot switches have an external lead which allows them to be configured either way.
If both of your switches are the same type and are wired correctly, they should work the same.
If you suspect that one is defective, try swapping them.

power coming in from the breaker box: black wire will go to line-hot screw, and the white wire will go to the line-white screw. the switch wires coming out of the back of the gfci- 1 will go to the load-hot screw & the other black wire will wire nut to the black wire going to the light. the white wire going to the light must go to the load-white screw.