Poloma gas demand heater only getting warm water not hot 10y old.

RTG-95XP Item Name: Outdoor Rheem Tankless Water Heater RTGL-74XP Item Price: $910-$1100 Gas Type: Propane Venting: No Item SKU: Rheem RTG-95XP replaces RTG-74XP Product Description: Rheem Tankless Water Heater RTG-95XP

Be aware of this --- http://www.cpsc.gov/cpscpub/prerel/prhtml07/07108.html

And this ---

Rheem RTG-95XP replaces RTG-74XP

This makes getting information hard to come by. Please use the link below for information.

http://www.rheemtanklessonline.com/contact.php

check for pilot but im sure that the pilot is on demand thats what makes these things so cool and inexpensive to operate. try having someone turn on the hot water while looking for ignition. if there is nothing it may be a relay. im not sure but if you open it up check for a 3 amp fuse its green. all the new furnaces with mother boards have a fuse. I am not really a heating guy but i have been looking into on demand systems and sat in a training session at the plumbing supply. never hurts to try and help.
if its not a fuse or the ingniter isnt functioning you may need to call a heating person who knows on demand or check Bosch on line maybe they have the trouble shooting guide if you dont.

sorry that all i can suggest hope it helps

First, let water heater heat up until it shuts itself off. Now carefully, ( it should be hot) open pressure relief valve slightly and catch some hot water in a cup or container. Compare it to what comes out your tap, that you say is warm only. If that water from pressure relief feels hotter, then check your by-pass valves for proper operation and position on rear of water heater, as it may be in a position that is allowing cold to mix with hot, creating warm. Cold line will go direct in the bottom fitting and hot will come out top fitting, and make sure any valves in between those 2 lines are in off position. If all is well there, or water from pressure relief is only warm as tap as well, then buy a new thermostat and ECO for that particular model water heater from RV dealer/service center, and replace them. They are behind rubber cover on upper left side on water heater. When cover is off, they are held against tank by 3/8 nut. When you replace it, snug nut up good but be careful not to go too much and snap that small brass stud that nut goes on. Pay attention to position of old one, so new one goes same way.

If you have the same Autocirc product I have, then it cannot be taken apart. The timer seems to be connected and sealed together with the pump. If yours is different, answer back with the wires that you can see and we'll see if the timer can be by-passed.
http://waterheatertimer.org/Water-heater-recirculation-system.html

With the ordinary Grunfos-type pump that is not on a timer, you can add a switch and have the pump work on demand as you describe.

And they make a product that does the specific job you describe. It's called a Demand Pump. Link above shows two different types at page bottom.

I have not tested either Demand Pump shown. They operate on-demand ... when you activate the pump, the pump quickly brings water over from the hot water heater.

So the Demand Pump has a higher volume pump than the Autocirc or Grunfos.

I question a two things about the Demand Pump. 1) How will the increased pump pressure affect local pipes, especially supply tubes under a sink. 2) How HOT does the pump get? If pump gets hot, and it is located under bathroom sink next to paper goods, then that is a hazard. Some regional building codes don't allow ceiling light bulbs in closets because the bulbs get hot and start fires when people pack their closets full.

If you've checked at pressure relief valve ( careful, not to burn yourself just in case it is hot) by pulling lever and catching some water that comes out in a cup or whatever. If it feels hot out of there, check that by-pass isn't faulty. Not uncommon for valves to seize, and only partially open, or close, and end up mixing hot with cold.

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.

your thermocoupler is bad..

In most of the tankless water heaters the tempature of the warter is controled by the rate(amount) of vlow of the water passing through the unit. Turn down the flow of water going into the water heater and the water that is still passing through will be hotter. Carefully. A little at a time,so as not to be too hot.  

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.