Pentair Pool Products MiniMax NT Series Service Manual page 42

Troubleshooting
If the heater fires, shuts down and refires every 30-45 seconds and the Service Light comes ON and
goes OFF alternately with the Heat Light, this indicates that the Inlet or Outlet High Limit Switch is
sensing a temperature greater than 115° of 150° F., respectively. This is generally caused by a lack of
water inside the heat exchanger, while the heater is firing.
Things To Look For:
1. The pump is worn out.
2. The pump isn't pumping enough water.
3. The pump impeller is plugged.
4. A valve on the outlet side of the heater has been closed.
5. The pump is a 2 speed that is operating on low speed.
6. Something is blocking the water flow through the heat
exchanger.
7. The flow valve is defective or damaged.
Troubleshooting
The flow valve is installed in the inlet/outlet header and allows
a small portion of the water to pass through the heat exchanger
when the heater is not firing. When the heater fires, as the water
leaving the exchanger warms, the flow valve forces more water
into the exchanger by partially closing the by-pass opening.
You can test the flow valve by removing it from the heater and
placing the power element in hot water. If the power element
rod extends and forces the by-pass disc to move toward the
mounting plate and retracts when placed in cold water, the flow
valve is OK, but if it does not move, replace the power element. The power element is copper, so water
with a low pH (7.4 or lower) and or water velocity (too much flow) will cause the element to fail and the
heater will cycle rapidly.
If there is not enough water in the heat exchanger to prevent the heater from cycling, the inlet/
outlet header will be too hot to touch.
If you check all the water related causes of rapid cycling and do not find the problem, an electrical
nuisance shut down may be causing the cycling. (wiring connections, inadequate grounding, defective
or not properly aligned Flame Sensor). However, if you have followed the directions in the "BEFORE"
troubleshooting section, the wiring problems should be minimal.
4¼"
P/N NTSM03
RAPID CYCLING
Inlet High Limit
ADJUSTING FLOW VALVE
• Diverter.
• Power element.
• When replacing or adjusting the power
element, use a measurement of 4¼"
between the diverter and retention cap face.
42
Outlet High Limit
Rev. B 2-11-04