Hi there i recently had another gas appliance installed and the gas was turned off while this work was done, so my hot water service pilot light went out. the guys who did this work didn't relight the pilot. i don't have a manual for the uni - how do i relight the pilot. thanks

If keeping the thermocouple bypass pressed keeps the gas flowing to the pilot but the flame goes out when it is released in spite of keeping the flame going the customary amount of time, then either the flame isn't powerful enough to reach and heat the thermocouple bulb, the pilot flame or the bulb is out of alignment or the thermocouple is faulty.

If the flame is weak it indicates a blockage in the jet or the supply pipe.

Make sure your gas is not shut off.
Do you have any other gas appliances that are working?

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gregg_27a4d257e54e7920

There should be a trouble shoot guide on the hot water tank. I have had to do this many times. You just need to read the trouble shooting guide & be very careful. I hope this works for you.
D :)

You need to inspect and clean the air intake located on bottom of unit. Get more fresh air to the water heater and see if problem continues.
http://waterheatertimer.org/images/Flame-trap-inspection-325.jpg
http://waterheatertimer.org/images/State-select-air-intake-400.jpg

Instructions for lighting the unit are located on front of water heater.
Other possible causes include: bad gas control valve, dirty combustion parts, reverse draft down the stack (caused by wind and opening door inside closed utility room), low gas pressure, air in gas line, etc.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

Propane gas is heavier than air. So if you have a gas leak, then smell close to floor. Leave house immediately if you smell gas. Install a gas detector close to floor level near gas appliances.
Most water heaters today are extremely safe, because we experimented on prior generations of people, who then passed along their experience.

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

Suspects include: bad gas control, air in gas line, water dripping down vent, poor air supply, dirty air intake, very hot attic, negative pressure caused by tight house and other venting appliances and vent fans that cause backdraft down vent. Or combination of these problems.

Open following links for resources:
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

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

Open following links for pilot light help:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/pdf/Pilot-light-will-not-stay-lit.pdf
http://waterheatertimer.org/images/Negative-pressure.jpg
http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdf

Since pilot light goes out and can be re-lit, problem is probably not thermocouple, gas control valve, or air in gas line. But these things can factor in as contributing factors.
Problem is likely one of following or combination of following including dirty burner parts, tight house, incorrect vent lengths, negative pressure caused by other venting appliances, condensation dripping down into combustion area, and inadequate oxygen supply due to hot or closed-off room or attic location.

Gas water heaters draw air from surrounding area. If water heater is located inside house, then air has to enter home through cracks and when doors and windows are opened. Other gas appliances and vent fans also draw air from same indoor area. When other vent fans turn on, air can be drawn down the water heater vent and blow out pilot light.
Inspect combustion chamber to make sure there is no condensate water dripping down from incorrect vent that is putting out flame. If combustion chamber is dry, then close doors and windows. Turn on all vent fans and gas appliances that vent outdoors, and see if water heater pilot goes out.
Consult with plumber or product manual about proper horizontal and vertical lengths of vent pipe for your model. Have plumber clean combustion parts and inspect vent termination and check gas pressure and bleed gas line.
Add louver opening to outdoors so air can enter room where water heater is located.

The problem requires looking at manual and service handbook, except handbook doesn't show most recent water heater.
My first check point would be gas supply, and then vent draft, and then air supply.
Take off front cover and try lighting again to make sure air supply is not problem.
Review lighting instructions.
If there is no gas, and gas is turned ON, then gas control valve is suspect.

On-line manual for Reliance 909 gas
http://www.reliancewaterheaters.com/lit/om/manuals/186486-002.pdf
Reliance 2006 service handbook:
http://waterheatertimer.org/pdf/Reliance-2006-Service-Handbook.pdf

Other resources:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot
http://waterheatertimer.org/images/Test-water-heater-vent-1400.jpg
http://waterheatertimer.org/images/Water-heater-in-attic-800.jpg

Open following link for Bosch tankless troubleshooting resources, including Bosch contact information, typical manuals, error codes, tech support, parts, fuel-saver calculator, service bulletins, water heater forum, fixya links, disclaimers, and links for finding service technician.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Before calling service technician, read manual for fault finding and possible solutions.
Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.
http://waterheatertimer.org/pdf/Bosch_water-wizard.pdf
http://waterheatertimer.org/pdf/Bosch_13P_16P_In.pdf

Following links talk about keeping pilot lit, and describe location somewhat. Bosch water wizard has standing pilot light.
http://www.fixya.com/support/t2961646-water_wizard_10p_pilot_light_keeps_going
http://www.fixya.com/support/t2960079-bosh_water_wizard_10p_pilot_light_keeps
http://www.fixya.com/support/t6182021-bosch_10p_tankless_hot_water

1) The manual does not show diagrams you asked for.

2) Website that sells Bosch parts does not show parts for water wizard, nor does Bosch site for parts: Instruction manual says: replace pilot injector
http://www.boschhotwater.com/HelpfulResources/PurchaseParts/tabid/837/Default.aspx
http://www.houseneeds.com/shop/heatingproducts/waterheating/parts/bosch2400espartsbuy.asp#

3) Searching "pilot injector for Bosch Water wizard" turns up fixya questions which is generally bad news for do-it-yourselfer because it means information sources are through service technician.

4) As a general rule, tankless are not do-it-yourself repairs or installation because they are affected by so many internal and external factors, including air quality, air flow, venting, other gas appliances, gas pressure, gas supply, water pressure, water flow, plumbing problems, water quality, plus internal parts and including any combination of things listed above..
Replacement parts each come will disclaimer.

Add a comment with your experience so others with same-similar problem can benefit.
Send some photos so the internet can see the problem.
http://www.fixya.com/support/r6568559-post_photograph_fixya_questions_answers

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Look inside the water heater when it is heating the water, the flame should be blue. If it has yellow tips on the flame, it needs an adjustment to the air shutter. There is a nut on this air shutter to make this adjustment. This adjusts the air gas mixture. You may first try just simply tapping on the burner lightly to loosen any debris that may have built up and vacuum it out. MAKE SURE YOU TURN OFF THE GAS BEFORE CLEANING THE BURNER!! Also, check for drafts that may be blowing out your pilot light, Furnace register or outside drafts on windy nights. Some water heaters have an automatic shut down if the water heater gets too hot, so don't have it set to its hottest setting. Most water heaters only last about 10 years or so, It could be you are ready for a new one....Joe