Precisely matched orifice plates meter the air and gas into the mixer. The blower draws the air and gas through the mixer and forces it into the burner’s flame holder. A sealed heat exchanger surrounds the flame holder, discharging exhaust gases out the flue. PVC water piping connects directly to the manifold/header on the heat exchanger using PVC slip unions provided with the heater.
The outer manifold remains cool, which means heat sinks are not required. A thermal regulator and an internal bypass regulate the water flow through the heat exchanger to maintain the correct outlet temperature. The heater operator control panel board assembly is located on top of the heater.
Sequence of operation
An electronic temperature sensing thermistor in the manifold adapter inlet controls the heater operation. When the inlet water temperature drops below the temperature set on the operating control, the burner controller supplies power to the combustion air blower through a series of safety interlocks.
The interlocks consist of:
- The pressure switch (PS), which senses that the pump is running
- The high limit switch (HLS), which opens if the heat exchanger outlet temperature goes above 57° C (135° F)
- The airflow switch (AFS), which senses the pressure drop across the air-metering orifice
- The automatic gas shut-off (AGS) switch, which opens if the heat exchanger outlet temperature goes above 60° C (1 40° F)
- The stack flue sensor (SFS), which shuts down the heater if the flue gas temperature reaches 260° C (500° F)
The airflow switch (AFS) senses the pressure drop across the air-metering orifice. As soon as there is sufficient airflow, the AFS closes, shutting down the circuit to the hot surface igniter (HSI) that ignites the fuel mixture.
On a call for heat, the blower and HSI are energised. In roughly 20 seconds, the gas valve opens and ignition occurs. The HSI then switches to a sensing mode and monitors the flame.
The heater is equipped with a digital operating control that enables the user to pre-set the desired pool and spa water temperatures. The control enables the user to select between pool and spa heating, and features a digital display that indicates the water temperature