Where can I get an installation kit to replace existing hot water heater exhaust?

SOURCE: tp valve opening and dumping water

Certain water heaters can only handle so much pressure from the main line. There is a pressure controller between your water meter and you house, it's called a pressure regulator. You need to call a plumber to check and see if it needs to be adjusted or even replaced.

SOURCE: takes too long for hot water.

You need a recirculating line. You will have to hire a plumber to run a water line from the farthest fixture or to the fixture you are concerned about on the hot side and return it back to the water heater. this will cause hot water to constantly run throught the hot water line (via the recirculating line) and when you want to draw water from the fixture, you will already have hot water right at the line.
I know this works with standard tank water heaters, but it is a lil trickier with rinnai units(but very possible) if your plumber pleads the 5th and tries to sell you another unit call the Rinnai manufacturerand ask them how.

SOURCE: leaking water heater from top

water heater is rotten
go to home depot and buy a replacement heater
it might be posible to rent a water heater from the local electric co and they will install it for free and charge you 12-15 per month for the heater saves money and saves cash for install
if it breaks they replace it same for gas heater let them dicker arround wit the heater and pull there hair out somtimes it is beter to rent than to buy also you can get a biger heater if you want they usualy will suply a larger unit at the same price if it will fit in your space

SOURCE: Error code 13, replace

Before calling service technician, open following link for troubleshoot resources:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

The same error code and problem on one person's tankless unit can have different solution than another tankless unit.
This is because tankless require perfect operation of parts and sensors while being affected by incomming water and gas issues, and venting, plus plumbing factors.
Replacing one part is not always the fix, since that part interrelates with so many other parts, each affected by the operation of the other, and operation of the chip and integrity of wiring and wiring connections.

Read manual for yearly maintenance requirements, and calculate those costs when figuring anticipated $1-8 monthly energy savings from owning tankless.
Check that your region has reasonably-priced, qualified service technician for your brand before buying tankless. And check part list and cost of parts before buying any water heater because these factors weigh-in after a few years of operation.

Repair most tankless problems yourself, same day, any brand, for around $330.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Upvote the help.
And 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.

SOURCE: How to remove a hot water heater and replace a new one ?

Seems like if you need to ask such a general question, you need to call for help...a plumber

Testimonial: "It might be what you feel is a general question but since I am a women and not a know it all man.I justed wanted to know if it was an easy job for a do it yourself person or if a know it all man should do the job."