After changing to a new filter, we are only getting cold water, the water is not heating

I am not familiar with the model. Is this a 10 gallon water heater? the volume of water can not change. The temperature can usually be adjusted and even placed in vacation mode. Also the pilot light might be out, this would be the only thing I could think of that would stop all hot water. You mentioned output. If you are referring to flow this would be a restriction in you pipes possibly. If you have old galvanized pipes this would explain the reduction in flow. Also if this is a tankless water heater a reduction in flow would explain in not working at all. If the flow of water is not adequate enough a tankless heater will now turn on. If it is a Tankless water heater then there is a filter located on the cold side. To check this turn off the cold water, relieve the pressure by piping the TPRV Valve "Temperature, Pressure Relief Valve. Then take the cover off the filter. clean all that nasty gunk off the filter, reinstall it and you are back in business. The heater should be as good as new.

You probably need new a new cearamic insert (or two), but I can't point you at where to get it because I don't know where you are. Franke FR2 014 Cold Valve Seat For LB2200 Lil Butler 2 014 also known... Franke FR2 015 Hot Valve Seat For LB2200 Little Butler 2 015 also known...

It sounds like the cartridge is not properly seated against the O ring. I am not familiar with this exact model but remove the filter, check and be sure the o rings are ok and re install the filter.

It sounds like the cartridge is not properly seated against the O ring. I am not familiar with this exact model but remove the filter, check and be sure the o rings are ok and re install the filter.

Turn off your incoming cold water to the tankless. (you should probably do the same with your hot water out line just in case). find the black cap that screws sideways into the cold water connection on the bottom of the unit. unscrew the black cap. the filter is supposed to be attached but it almost always comes off. grab a screw driver and stick it in the hole that the black cap was covering. angle it and drag the filter out. you may end up putting a hole in the filter this way but it doesn't matter if you are replacing the filter anyways. once you pull it out make sure you have a little rubber washer on the new filter or else transfer from the old one. the new filter should actually attach itself nicely onto the black cap so once you've removed the old one all you have to do is screw the black cap/filter combo piece back onto the cold water connection and you're done.

I suppose I should mention you will want to have a bucket under the pipes and everything because your unit will empty all the water that was in the unit out of that hole.

Usually this type of fault is down to poor water flow. Basically you are asking the unit to work at a level below it's minimum output. Easy thing to try is to check any filters or water flow limiters in your tapware. Usually these are in the nozzle of the tap. I often take these out. The inifinty reduces water flow anyway and there is no reason to have water limiters. Try turning on two taps at once. If this stops the fault then you definately need to increase your water flow. Make sure the mains water is turned on full. Aslo you can check the cold water filter on the infinity. It's just above the cold water isolation tap (middle pipe as you look at it), turn that off first, the filter is a round plastic nut, unscreww it and clean the filter. Reconnect, turn you mains water back on.
There are other faults but this is by far the most common.

It is likely the inlet filter is plugged. this reduces the flow and then the heater adjusts the burn rate down to protect itself. the filter screens are small and plug easily. It would be a good idea to install a larger pre filter on these heaters.

If the lower heating element burns out the upper element will heat the top part of the tank then shutoff. homw depot/lowes etc should carry elements. 1 turn off breaker, remove element access cover (the 2 panels on the front of the heater) test for electricity at the reset button ( uppermost device in upper panel) to make sure power is off. 2 turn off water (I usually turn off the cold water main to stop water cross feeding into hot supply line back into heater) 3 disconnect the 2 wires on the lower element, test with continuity tester. shhould be no continuity between terminals and tank, but around 10 ohms between the 2 terminals. Check the thermostat for continuity if tank is cold thermostat should be closed ie zero ohms across the 2 terminals.
If stat is bad replace stat; disconnect wires push it up out of the spring clip insert new stat reconnect. If element is bad: drain tank. connect garden hose to tank drain valve, open tank drain valve turn water main on to clear rust sediment and get water flowing. Next remove filter screen from a hot water faucet then turn on ( a hot faucet upstairs or higher than tank drain). Now turn water main off, air will now go in through hot faucet and tank will drain, takes about an hour. Use a water heater element wrench about$10 to remove element(s) make sure no bits of rubber gasket are left in element opening- dig em out with a screwdriver if needed. Insert new element with its gasket and tighten. reconnect wires DO NOT TURN ON ELECTRICITY! BE SURE TO FILL WATER HEATER WITH WATER ! Turn water main back on -air will come out of the hot faucet for several minutes. When water runs without any air sputtering, turn off faucet and replace the faucet filter screen. check element(s) for leaks. turn breaker back on.

I have a triton opal shower.

I turn shower on low pressure and cold water. then no low pressure and piping hot water for a very short time then low pressure and cold water.

I've changed the solenoid and the little black plastic ball.

Help !