Timer stopped working after 2nd day of use. Display initially flickered and wouldn't respond to any of the buttons. The brand new batteries are fully charged but when removed and reinserted the timer makes a 3 second noise briefly allowing water to pass through the valve after which it goes quiet and closes valve. Display never lights up.

Question posted under Intermatic ST01C, but Timer is not 100% identified since ST01C is battery powered, and should not lose programming or stop working with ordinary power outage.
Most digital timers have a battery or capacitor back-up for power outage.
Add a comment with description of timer buttons, or open link below to see most brands of in-wall timer.

Open following link for to identify Intermatic ST01C and Ei600 and download instructions:
http://waterheatertimer.org/ST01C-program.html#battery
ST01C timer has a battery backup. Power outage will NOT cause battery-powered display to fail, but power outage and power surge can cause any electronic timer to fail.
So either the battery went dead, or power surge ruined timer, or you don't have ST01C timer.

If ST01c display is not showing, then replace battery and then reprogram current time -or- manually re-set timer and then reprogram timer.

Question posted under Tork SS720 timer.
I don't have repair for defective timer that worked before and stopped working.
If this is new timer, then add a comment and explain wiring in exact detail, and include what you mean by 'dimmed' mode.

Timers have 1 year limited warranty.
Timers are affected by line noise, and generally cannot be connected to a dimmer.

SS720A timer is robust 120Volt single-pole 7-day programmable timer, rated for 15Amp up to 1 HP.
The larger the amp load, the shorter the lifespan for electrical devices.

Last step troubleshoot for programmable timer is to reset timer and reprogram.
Reset timer by pushing in reset button for several seconds.
If functionality is not restored, then timer has gone bad.

Tork SS720 is identical to GE15071 timer sold at Home Depot.
Buy another timer, and return defect in new package.

http://waterheatertimer.org/Tork-consumer-timers-and-manuals.html
http://waterheatertimer.org/pdf/SS720A-Tork-In-wall-manual.pdf
http://waterheatertimer.org/GE-timers-and-manuals.html#15071

I don't have answer for defective timer. Buy another timer if everything below checks out:
59018 7-day timer has limited 1 year warranty, and appears to be made by Tork
Timer is for 120Volt single-pole only.
Rated for 1000 watt tungsten, 8A ballast, 1/4 HP
Push reset button with toothpick > not necessary to press-and-hold other button to accomplish reset.
After reset, 12:00 am Monday should display.
Programs are deleted. Reprogram timer.

To check, change and delete specific programming, press PROG key until selected program displays, and then set new programming >>> or press-and-hold MODE button and press PROG button again to delete selected program.

Timer has non-replaceable 30-day carryover battery and does not lose programming after power outage, and will retain programs until battery is depleted.

Review wiring:
Hot to timer black.
Neutral to timer white.
Load to timer red.
Ground to timer green.

Lights will blink if timer red and timer white are connected to load together.
Timer will not function if timer black and red wires are reversed. Display will not show.

http://waterheatertimer.org/Woods-timers-and-manuals.html#59028

Timer is not identified.
If digital timer does not function as before, try resetting timer and then re-program.
If timer has battery, then change battery and reset timer.
If reset does not restore functionality, then timer has gone bad. Most in-wall timers have 1 year limited warranty.

Below are common 7-day timers, but there are many different brands:

You posted under Woods 7-day timer: except Woods timer does not astronomic dawn dusk function. Woods 7-day is same as Tork 7-day and GE 7-day, and they do not have astronomic function.
http://waterheatertimer.org/pdf/Woods-59018-59028.pdf
http://waterheatertimer.org/Woods-timers-and-manuals.html#59028
Reset button is small round button.
Push in reset with toothpick or paper clip.
Then reprogram timer.

If you have Intermatic ST01C or EJ500 battery operated timer: Replace battery, then to reset timer: push-and-hold ON_OFF button, and then push reset button. Keep holding on-off button until display changes. Release on-off button and display will flash 12:00. Then reprogram timer.
http://waterheatertimer.org/Intermatic-timers-and-manuals.html

If you have Utilitec astronomic timer, then press reset button and reprogram:
http://waterheatertimer.org/Program-wire-Utilitec-LW60419.html

I'd buy a new timer of a different brand. I have tried several of these and there are fundamental problems. In my case. I set the frequency. OK. I set the time. OK. After about 10 seconds it shuts off and doesn't start again. Same problem with 2 units. It I'm tired of messing with it. I certainly wouldn't trust it if I had to be out of town for a few days. Look into the DIG EZ. I've had great luck with them.

Please add a comment with brand-model-number or full description of timer.
I will look up manual and give best answer possible.

http://waterheatertimer.org/Woods-timers-and-manuals.html#troubleshoot
Some timers have reset button then lets you revive old timer that stopped working.
Some timers will not display if timer wired incorrectly.
Some timers have rechargeable battery that must be charged 1 hour before starting.
Rechargeable batteries wear out and timer goes bad.
Some timers have battery that needs replacement.
Timers with battery of any kind will stop displaying if exposed to cold temperatures over several days.

Add a comment for more free help.
Also take advantage of fixya expert assistance live.
For a price, expert works with you via e-mail while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.

The timer initializes in MANual mode.
To reach SET UP, press MODE button until set-up displays.
If MODE button does not work, then timer has a serious glitch.

1) If this is a timer that worked correctly before, and recently malfunctioned, then try replacing CR2 battery. The timer display and programming functions are dependent on the battery, so when battery starts going dead, the timer does odd things.
http://waterheatertimer.org/ST01C-program.html#battery

2) Try resetting timer.
Hold down ON-OFF button and then push reset button for two seconds.
Release Reset button, but keep holding ON-OFF button until display flashes INIT.
Then release ON-OFF button and 12:00 displays.
Following page has easy to follow programming steps:
http://waterheatertimer.org/ST01C-program.html

3) ST01C has 1 year limited warranty, and people write in about defective timers each day.
There are no repair parts other than the battery.
Manual says when all other attempts fail, then reset timer as described above.
http://www.intermatic.com/products/timers/consumer%20indoor%20timers/in-wall%20timers/st01c.aspx

4) If this is new timer, then exchange defective timer for new timer.
I test timers: 4-6% arrive defective. Many go bad first year or two. Some last quite a while.
Some programmable timers can be reset and the timer recovers, as described above.

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, fixya expert speaks with you over phone while you work on timer.

http://www.intermatic.com/products/timers/consumer%20outdoor%20timers/digital%20timers/hb88rc.aspx

HB88RC is 7-day plug-in digital outdoor timer that uses AA battery installed on back of timer to power the display.
People write to fixya frequently report Intermatic timer stops working after replacing battery.

To check if your timer is still functional:
Press and hold clock button.
Press Day button until current day shows in display.
Press Hour until current hour shows in display
Press MIN until current minute show in display
Release clock button.

If current time shows in display, then timer is probably still good.

To set programs:
step 1) Press PROG button until 1 and ON show on display.
This is program1 ON.
Press day button until choice of days shows for program1 ON
Press hour until hour for program1 ON shows
Press MIN until minute for program1 ON shows.

step 2) Press PROG button until 1 and OFF show on display
This is program1 OFF.
Press day button until choice of days shows for program1 OFF
Press hour until hour for program1 OFF shows
Press MIN until minute for program1 OFF shows.

step 3) Press PROG button until 2 and ON show on display
Repeat steps above to set program2 thru program7

step 4) When programs are set, press CLOCK button to return to current time

step 5) add a comment for more help

I just bought a Sportline 241 last week. The instructions are as follows. Note that there are no instructions for setting the 12/24 hour time option. Mine is in 24 hour mode (which is what I wanted), but I do not recall if it arrived that way or if I stumbled onto this mode when setting the time/date or alarm functions.

I hope this helps.


SPORTLINE 241 WALKING ADVANTAGE KEYCHAIN STOPWATCH

FEATURES:
24 hour stopwatch
Time-of-day and calendar
Alarm clock
12/24 hour time option

BATTERY:
Replace with LR41 battery

TO SET TIME AND CALENDAR:
From normal time display, press MODE button three times to enter Set Time/Date Mode. Seconds is automatically selected.
Press SPLIT/RESET button to cycle through minutes, hours, day, month, day of week, seconds.
Press START/STOP SET button to change digits on any of the above (seconds only: resets to 00).
Press and hold START/STOP SET button to advance digits rapidly.
Press MODE button once to return to normal time display.
From normal time display, press and hold START/STOP SET button to see the month, day, and day-of-week.

TO SET ALARM:
From normal time display, press MODE button twice to enter Set Alarm Mode. Hours is automatically selected.
Press SPLIT/RESET button to cycle through minutes and hours.
Press START/STOP SET button to change digits.
Press and hold START/STOP SET button to advance digits rapidly.
Press MODE button to return to normal time display.
From normal time display, press and hold SPLIT/RESET button to see the alarm time setting.

TO ARM/DISARM ALARM SOUND:
From normal time display, press and hold SPLIT/RESET button, then repeatedly press START/STOP SET button to arm/disarm alarm sound.
Alarm will sound when indicator shows in upper right corner.
Release SPLIT/RESET button to return to normal time display.

TO ARM/DISARM HOURLY CHIME SOUND:
From normal time display, press and hold SPLIT/RESET button, then repeatedly press MODE button to arm/disarm hourly chime sound.
Chime will sound when dashes appear along top of display.
Release SPLIT/RESET button to return to normal time display.


STOPWATCH OPERATION - GENERAL:
From normal time display, press MODE button once to reach stopwatch timer display.
After use of any stopwatch feature, press MODE button once to return to normal time display.

START-STOP (TIME-IN/TIME-OUT) TIMING:
With stopwatch timer on display, repeatedly press START/STOP SET button to start or stop the timer. When timer is stopped, press SPLIT/RESET button to reset timer to 0.

SPLIT TIMING:
With stopwatch timer on display, start the timer with START/STOP SET button. Repeatedly press SPLIT/RESET button to split or release the timer. Press START/STOP SET button to stop the timer. Press SPLIT/RESET button to reset timer to 0.

1-2 FAST FINISH:
With stopwatch timer on display, start the timer with START/STOP SET button.
Press SPLIT/RESET button for STOP #1.
Press START/STOP SET button for STOP #2. The stop time for #1 will now be shown.
Press SPLIT/RESET button. The stop time for #2 will now be shown.
Press SPLIT/RESET button to reset the timer to 0.