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Hi-E Model EPH Pool and Spa Heater
SECTION 1.
General Information
This manual provides maintenance instructions for the
Teledyne Laars Hi-E Model EPH 300 pool and spa heater.
SECTION 2.
Overall Operation and Service
2A. Heater Control Components
Some of the heater control components are the same
as those used in conventional heaters, but others are
designed specifically for the Hi-E EPH 300 heater (see
Fig. 1).
The following paragraphs describe the special
controls and their operation.
2A-1. Pressure Switch
The pressure switch is a safety device that senses
water pressure or back pressure between the heater and
the pool or spa when the filter pump is operating. The
switch is factory set at 2 pounds per square inch (psi)
(14 kilopascals [kPa]).
When the switch senses adequate water pressure, it
closes, allowing the heater to fire. The switch opens any
time water pressure is below 2 psi (14 kPa) and remains
opens, preventing the heater from firing, regardless of
the temperature control setting. If the water pressure is
too high, the switch remains closed, allowing the
heater to fire even if the filter pump is off. Therefore,
the height difference between the heater and the pool or
spa water surface level must fall within the correct
range.
2A-2. High Limit Switches
The Hi-E heater has two disk-type high limit
switches to meet ANSI safety requirements. The high
limit switches open if the temperature of the water
exceeds the respective limits, shutting down the heater.
The high limit switches close and automatically reset
when exposed to cool water flow for a short time.
The 150 degrees Fahrenheit (°F) (66 degrees
Celsius [°C]) high limit switch senses the temperature
of the hottest water as it leaves the heat exchanger.
The 135°F (57°C) high limit switch senses the tem-
perature of the mixed water after it leaves the heater
and mixes with water that bypasses the heater inlet to
the outlet.
Water can overheat if the water flow rate drops,
usually due to a flow restriction in the heat exchanger,
pool piping system, or a dirty filter. A broken disc or
spring in the automatic flow control valve can cause
the 150°F (66°C) high limit switch to open, allowing
too much water to bypass the heat exchanger, corre-
spondingly lowering the water flow rate through the
heat exchanger.
Figure 1. Component Location
