Pentair MiniMax Plus Service Manual page 30

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 High Limit Switches (installed into the inlet/outlet header) are
sensing a temperature of 150 degrees.
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 doesn't pump enough water.
3. The pump impeller is plugged.
4. A valve on the return side of the heater has been turned off.
5. The pump is a 2 speed and is on low speed.
6. Something blocking the water flow to the exchanger.
7. The flow valve is defective or damaged.
The flow valve is installed in the inlet/outlet header and
allows water to by-pass when the heater is not firing.
When the heater fires, the flow valve forces more cold
water into the exchanger by 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 O.K., 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, the cycling may be caused by an
electrical nuisance shut down. (Wiring connections, inadequate
grounding, pilot ignitor defective or not aligned properly or
defective ignition wire.) If you have followed the directions
"BEFORE" troubleshooting, the wiring possibilities should be
minimal.
Either Flow Valve will work in ALL MiniMax heaters.
P/N 38033
NOTE
NOTE
CYCLES RAPIDLY
Flow Valve
Installed Here
Newest - Production Date 8/99
3 0
INLET/OUTLET
HEADER
Power
Element
Rev. C 12-1-00