How
to troubleshoot
Intermatic WH21 timer
 WH21- larger image WH21 / 25 amp water heater timer WH21 manual |
Avoid
electrocution/ Tape multimeter leads to wood Stand on dry boards Do not touch metal Wear dry clothes Do not touch wet water heater Do not touch wet timer box Wear insulated gloves Do not hold metal object in mouth Do not lean into anything made of metal Buy cheap multi-meter at box store. Set to 250Vac for tests. |
240Volt wires can be white-and-black or red-and-black. Recommend 30 amp breaker and 10 gauge wire.
See Basic water heater circuit
WH21 troubleshoot
If timer dial is rotating, and keeping good time, then clock motor is good.
If the dial is not rotating, then clock motor might be bad.
There is no replacement clock motor for WH21.
If dial is not rotating, pull off the timer dial and then reset to make sure it is properly seated.
Timer dial must be pushed inward for dial to turn water heater on-and-off.
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If you cannot get dial to rotate correctly, then check wiring. Check that only copper wire and no insulation is inserted under pressure plate. Check that screws are very tight against copper wire, and there is no evindence of melting or burning. Use nose to smell for burning, and ears to listen for crackling. Do not mix 2 different gauge wires under same pressure plate, Do not put solid copper wire and stranded copper wire under same pressure plate. |  |
Manually rotate dial and see if water heater turns ON-OFF. Listen for bubbly-fizzing sound by putting ear against water heater. If tank is fully cold, then upper element should turn on. If tank is fully heated, then no element should turn on. If lower part of tank has cooled, then lower element should turn ON. How electric water heater works Troubleshoot electric water heater
Check for 240Volts across Line1 and Line2 on timer. Electrocution danger. Observe safety precautions shown on left.
Check that each Hot Line1 and Hot Line2 test 120Volts to green ground screw.
If you do not have 240Volts across Line1 and Line2, then circuit breaker might be tripped, or circuit breaker is loose on busbar. Action: Move wires to another same-amp circuit breaker. Test electricity to water heater
Terminal block has 3 screws: 1-2-3. Far right screw #3 is turned ON-OFF by timer. Other two screws #1-2 remain hot at all times. Test far right #3 screw to ground screw. When timer is ON, test should read 120Volts. Manually rotate timer dial. When timer is OFF, test should read NO volts. If test shows that timer is not turning ON-and-OFF, then timer is bad or trippers are worn and need replacement.
If dial is rotating correctly, but water heater never turns on-off, then trippers might be bad.
WH21 uses 156EB1945A trippers (set includes 2 silver and 2 brass trippers)
Intermatic trippers and parts Order trippers from Intermatic
To stop timer from turning water heater ON-OFF, pull time dial outwards.
Timer must be reset for current time after power outage.
WH21 manual
Upgrade to WH40
Same as T104 except with convenient override lever
Larger image
Upgrade to better timer.
Buy heavy-duty 40-amp WH40 or T104 timer as replacement.
Only 1 difference between WH40 and T104: WH40 has manual override that sticks out of enclosure.
Both WH40 and T104 are idential otherwise: Both are heavy-duty and have replaceable 156T1978A trippers and WG1573 clock motor.
Both WH40 and T104 run cooler with less amp loss from heat, than 25-amp WH21 timer
How to wire WH40
How to wire T104
See all Intermatic water heater timers
See more water heater timers
Installation requires contactor. Timer turns contactor ON-OFF.
See timer installation
See GE 15070 timer
Volts x Amps = Watts
Watts divided by Volts = Amps
Most residential water heaters are non-simultanoeus. This means both elements are not ON at same time.
How electric water heater works
How to wire thermostats
Calculate safe maximum for timers/ electrical circuits
Read label on side of water heater for element wattage. Element wattage is tank wattage.
For example: If water heater has 5500 watt elements: 5500 watts divided by 240Volts = 22.91 amps
4500 watts divided by 240Volts = 18.75 amps.
Electricicans use 80% rule for safe maximum. WH21 is rated for 25 amps x .8 = 20 amps.
Calculation shows that WH21 is beyond safe-maximum with 5500 watt water heater. This means WH21 will run hot and not last as long.
If electrical device is run at-or-near maximum amp rating, the device will not last as long because of heat.
Same as running a car at full throttle. Car will not last as long.
In contrast, 40-amp WH40 and T104 timers are better long term investment for water heater timer.
WH40 and T104 are rated for 40 amps, so they withstand more amperage without heat loss, and will last longer.
How to wire WH40
How to wire T104
Calculate safe maximum for water heater circuit
If residential water heater is connected to 20 amp breaker and 12 gauge wire, then the same overheating problem occurs over time.
Circuit breaker will not last as long, and damage can occur to busbar.
See basic water heater circuit
20 amp breaker is subject to 80% safe-maximum rule.
20 amp circuit breaker x .8 = 16 amps. So safe maximum for 20 amp breaker is 16 amps.
As shown above, 4500 watt water heater draws 18.75 amps. And 5500 watt water heater draws 22.91 amps.
So 20 amp breaker with 12 gauge wire are rated too small for most water heaters. Over time the breaker can wear out sooner due to overheating.
Recommended that all water heaters be connected to 30 amp breaker and 10 gauge wire.
Safe maximum for 30 amp breaker x .8 = 24 amps.
30 amp breaker and 10 gauge wire run cooler, with less heat loss and more efficiency. Circuit breaker and main box last longer with less chance for heat damage.
Figure Volts Amps Watts for water heater
