Temperature with my on demand water heater is inconsistent

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Call a qualified service tech immediately.
Gas explosion indicates dirty combustion parts, and gas is not fully igniting when tankless turns on the gas. So gas builds up and then explodes causing serious damage to tankless, and serious risk to homeowner.

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1) Guesses: Sounds like a bad single-handled faucet cartridge, or low water flow at faucet, or clogged water filter.
Replace faucet cartridge, clean the aerator, and/or clean sediment out of pipes below sink, and clean water filter at tankless unit each month.

2) For exact measure of problem:
Typical faucet can have 2 gallon per minute flow rate.
2 gpm flow rate means faucet fills 1 gallon container in 30 seconds. Test faucet using 1 gallon container and a cooking timer to get flow rate.
Clean aerator to improve flow rate. Compare kitchen flow rate with other faucets in home.
http://waterheatertimer.org/Low-hot-water-pressure.html

Most homes have 1/2" diameter pipe running to kitchen faucet.
100 feet of 1/2" diameter pipe holds 1.2 gallons of water. This assumes no sediment build-up inside pipes.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Assuming only hot is turned on: If faucet is 100 feet away from water heater, and pipe diameter is unobstructed 1/2" diameter, and faucet has 2 gallon per minute water flow, then hot water should arrive in 36 seconds.
50 feet away, and hot water should arrive in 18 seconds.

If kitchen has single handled faucet, and the handle is raised in the middle, then equal amounts of hot and cold water are drawn at same time. This doubles amount of time for hot water to arrive.

If single handle faucet has a bad cartridge, then faucet can have crossover.
Crossover means that cold water can enter the faucet even if faucet is turned to hot.
Bad single-handled faucet cartridge can delay or stop the arrival of hot water.
http://waterheatertimer.org/Crossover.html

Tankless require maintenance including cleaning combustion parts yearly, de-lime heat exchanger frequently, and clean water filter each month.
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

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http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html#flow
1) Tankless require minimum flow rate before burner will activate.
2) Sounds like the water pressure drops quickly when faucet turns on. This implies combination of problems including sediment build up inside lines, crossover at single-handled faucet, or sediment filter clogged or water softener clogged.
3) Low flow faucets can reduce needed flow rate.
4) Other problems can contribute: sensor failure, loose wires, PC board failure, high temperature setting, cold incoming water temperature during winter months.

We probably need more information to give a good answer.
You report 2 different problems occurring at once: Low pressure and Low temperature.
If this is tankless water heater, then Low pressure and Low temperature might be related, and you probably need a service technician to diagnose and repair cause.

If this is tank-type water heater, look at label on side of tank for type and brand of heater.
Is it gas or electric water heater? Troubleshooting is totally different for each.

Is water pressure pressure low on just the hot side faucet, or is cold side faucet affected too?
Are all hot faucets affected by low pressure?
If you have a dual handle faucet, open hot side only and check if hot water that comes out is hot as normal.
This will say if problem is pressure or temperature.
Tank-type water heater usually won't have both these problems occur at one time, but water heaters work in funny ways sometimes.

Add a comment to this post, or re-post your question with details so the experts can give a solid answer and not guess.
Also you can post water heater questions on pro water heater forum:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

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When a tankless is installed, they are usually set up with a recirc. Theis keeps the water continuously heating to some degree.
When a tankless is installed into a home it has nothing to heat the water that is sitting in the pipe from its faucet to its heat source. Now as soon as you turn on the faucet, you have to let all that cold water run out until the newly heated water comes out from when you started the faucet.
You could measure the volume until heat and it will be pretty much the same every time for a given faucet.

The fact that your faucets are low flo is only part of the factor involving time it takes to get hot water. Another factor is volume. The diameter of your pipes makes a difference. You can remove the low flo restrictor from the faucet farthest away to speed up the process at least a little.

There is a minimum water flow required to operate your Bosch tank-less water heater. It is around .75 gallons a minute. There are three things you can do to help the flow.
1.Turning the temperature down will help increase the flow.
2. Installing higher flow aerators on your faucets.
3. Clean the Bosch tank less water heater.
You are not alone in having this issue. The most common problems are low flow faucet aerators and low flow shower heads.

Tankless water heaters normally take a little longer than a regular heater to provide hot water because they have to start and get warmed up. I'm guessing the heater uses a pilot light and that the short amount of hot water when you turn on the tap is hot because when the water is sitting still in the heater the heat from the pilot light is enough to get it hot. The tub faucet will get hot a lot faster than the shower because it lets a lot more water through and empties out the pipes faster than the shower. You could probably speed things up by letting the tub faucet run on completely hot for like 10-15 seconds and then turning on the shower.

I found a way to get warm water in the shower, but I'm not sure it qualifies as a solution. After trying everything else I thought that maybe when I was feathering the faucet in the shower toward the cold side so I would get warm water that at a certain point it blocked the flow on the hot water side enough so that the sensor in the hot water heater sensed there was no demand in the line and it shut the water heater off. To test this, I went to the kitchen and turned the kitchen sink faucet all the way to the hot side and then turned it on so that I got a small flow of water. I waited for the water to get hot to be sure the hot water heater was working. Once it was hot, I left it running to keep demand in the line and then I went to the shower and turned the faucet on. When the water got hot I started feathering the control towards the cold side and soon I had warm water. So I think I'm right in that the sensor in the hot water heater was shutting the water heater off when the demand in the shower was lowered to a certain point when I was trying to adjust the water temp in the shower.

So now I can get warm water, but it means I have to leave the hot water running at another fixture in the house to create a false demand in the system so the hot water heater doesn't shut down. Is there a way to adjust the senor in the hot water heater so that it will stay on when I'm using the shower only, so I don't have to waste water by running another faucet when I want to take a shower?

An on-demand, or tankless, water heater is a system for heating water as it passes through the pipes, usually very near the point of use. Traditional tank water heaters bring the water to approximately 140 degrees Fahrenheit (60 C), in order to ensure the water supply lasts long after the heater turns off. Since this is obviously far too hot to be pumped out of a shower of faucet, cold water is added to the mix in the pipes. Coupled with the loss of thermal energy over time, the average tank heater has an efficiency of approximately 80%. On-demand water heaters have a number of advantages over their tank-using counterparts. While tanks often degrade over time and begin leaking, the apparatus used in an on-demand water heater is much less susceptible to the burdens of age, and will often outlive the house they're installed in. The amount of energy used is a fraction of that used in a tank water heater, due to increased efficiency and a much smaller window during which a heating source is in use. While tank hot water heaters can, and often do, run out of hot water after a number of showers, on-demand heaters provide a never-ending supply of hot water, ensuring that warm water is always available when needed. A tankless water heater can cost between $500 and $1500, and they most commonly use either electric or natural gas energy to heat the water. Most mid-sized households report an energy savings of approximately 25-45% for a gas or propane heater, and up to 50% with an electric heater, over using traditional tank heaters. Water is usually set to a maximum temperature of 120 degrees Fahrenheit (49 C), though many heaters allow for custom setting of the maximum temperature via remote control. Outflow rates range from 8-14 gallons (30-53 litres) per minute. Installation for most tankless water heaters is incredibly easy, involving simple plumbing. In the case of electric heaters, all that is required for a fuel source is to plug the heater into an outlet and begin heating your water. Some modern on-demand water heaters can incorporate a solar preheating system. This system uses a traditional solar heating system and tank to bring the water nearer to the desired temperature, saving substantial energy use in the final on-demand heating. A solar preheating system costs between $500 and $800.