How do I adjust water temperature after valve has been installed

The lit red button may be an indicator that the water temperature inside the water heater flow channel has become too hot. If the outflow facet is adjusted to allow more water outflow (opened more) the water temperature should drop some and therefore with increased water flow, the temperature inside the water heater will also decrease. Or, if there is a manually adjustable outflow valve on the water heater, adjusting it to a more open position would also decrease the internal temperature.

To adjust the thermostat, turn off the water heater. Then remove the access panel(s) and any insulation. The access panels are above the drain valve. Take a small flat blade screwdriver and rotate thermostat dial pointer. (The lower temperature settings are to the right.) Replace the access panel(s) and insulation and then turn on the water heater. Do not remove the protective cover on the thermostat.

Wait for water to heat and then check the temperature at various faucets. Make sure to adjust the anti-scald temperature limiter at any faucet that may be accessed by a small child or adult who might be injured by high water temperatures. (Just put a thermometer in the flowing water. Check the faucet installation information. The high temperature limiter will be under/behind the handle for single handle fixtures.)

I hope this helps.

Cindy Wells

It *may* not be a problem with the water heater itself necessarily. When you say "keep adjusting the water temperature when you're taking a shower" I presume you're talking about turning the shower hot/cold knob(s) and not the temp thermostat on the water heater itself.
If so, when it starts to run colder, turn the knob all the way to full hot. Is the water then very hot? If so, the water heater is working fine & doing its job, and the problem is likely to be in the shower faucet mixing valve itself. Sometimes a faulty one will expand the inner seals/cartridge as hot water flows thru it, and starts to (wrongly) restrict the hot water flow, thus causing the constant need to "turn the dial up a notch".

I recommend safety changes to prevent ruptured water heater and assorted leaks.
135 degree hot water.
Maybe replace TP valve if it is dripping.
Drip pan under water heater with 3/4" drain line to outside.
Expansion tank on incoming cold water line to absorb pressure build-up, and prolong life of tank and plumbing.

Here's why:

1) Yes you can have scalding hot water.

2) I recommend 135 degrees since that will burn the evil right out of ya. And generally kill clothes washing bacteria.
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html

3) 150 is dangerous and can seriously burn skin in 1.5 seconds. Not safe around children and elderly.

4) Temperature settings on electric water heater are approximate, since thermostats are calibrated approximately, and read temperature through tank wall.

5) Also if you want to increase amount of hot water for high-consumption household, then setting tank temperature upward is one solution since more cold water is mixed with hot, so amount of hot inside tank goes further.

6) High temperature can cause TP valve to release water.
TP valve is pressure-temperature safety valve. Do NOT cap off.
Rating should be 125 psi and 180 degrees ... but all things water heater are approximate, and TP valves need replacement now and then.
It is not recommended by water heater manufactures to use 150 psi TP valve when water heater came with 125 psi. Rating shows in small print on end of TP. New TP valves sold at local hardware. Let tank cool before installing new one.

7) Higher temperature and high pressure can rupture tank.
Pressure over 80 psi shortens life of water heaters and plumbing fixtures. Put BTG100 pressure gauge on water heater drain valve to check pressure.

8) You need a drip pan with 3/4" drain line to outdoors, or to drain vent line, to prevent flood caused by ruptured water heater.
Turn water heater off when going on vacation.
Inspect water heater each 6 months.
Drip pan available at local home center or hardware:
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#drip

9) Heated water expands and puts pressure on tank and pipes.
Water does not compress... so when water gets hotter it expands against tank wall and against pipes.
Especially in closed system (check valve present) when system is without expansion tank.
Expansion tank is installed on incoming cold water line.
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#expansion

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

More information is needed.
Water heater is not identified.
Add a comment with more information from label on side of tank.

If you have gas water heater, then open following links to identify gas valve, and download error code diagnostic and possible service manual:
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html#intelli
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

For power vent water heater with Honeywell gas valve: three flashes indicate pressure switch or blower temperature switch not working.
Typical causes appear on page 13 on manual: can be bad blower, bad switch, blocked vent, exhaust temperature too high.
http://waterheatertimer.org/pdf/Icon-gas-valve-error-codes.pdf

The Atwood temperature adjustment is on the gas valve.
There is a metal lever sticking out.
http://waterheatertimer.org/gas-water-heater-timer.html#Atwood
Move the lever one direction, and if burner turns on, then move lever other direction to lower temperature.

If your gas valve is different, you might find answer on following page:
http://waterheatertimer.org/How-to-adjust-temperature-on-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.

Before you install the temperature control knob, adjust the valve body (47111) with a wrench to set the temperature to "100 degree or close to it". Now, place the limit ring to tdc (top dead center) and control knob with the red 100-degree align to it. Your problem may have been the valve's temperature setting is out range when you installing the temperature control knob.

Before you install the temperature control knob, adjust the valve body (47111) with a wrench to set the temperature to "100 degree or close to it". Now, place the limit ring to tdc (top dead center) and control knob with the red 100-degree align to it. Your problem may have been the valve's temperature setting is out range when you installing the temperature control knob.

Try this before replacing the shower diverter valve.

If this problem is isolated to the shower only, then I would suggest that the shower diverter valve is equipped with an "Anti-scald" safety feature that can not be adjusted, however the temperature regulator/thermostat on the water heater can be adjusted to a lower temperature so as to not activate the the "Anti-scald".