Where is the pressure switch adjustment knob on Hayward h200fd?

Testing the water pressure of your Hayward gas heater is a relatively simple process. Follow these steps to check if your water pressure is working properly:

1. Turn off the Gas Heater: Before performing any tests, make sure the gas heater is turned off to avoid any potential accidents or injuries.
2. Check the Pressure Gauge: Locate the pressure gauge on your Hayward gas heater. It is usually located on the front panel of the unit or near the plumbing connections.
3. Observe the Pressure Reading: The pressure gauge will display the current water pressure. It is typically measured in pounds per square inch (psi). The optimal water pressure for most pool heaters is usually between 15 psi to 25 psi, but it's essential to check your heater's manual for the specific recommended pressure range.
4. Turn on the Pool Pump: Ensure that the pool pump is running, as it is responsible for circulating the water through the heater. The water pressure will be at its most accurate when the pool pump is operating normally.
5. Monitor the Pressure: While the pool pump is running, observe the pressure gauge to see if the water pressure falls within the recommended range. If the pressure is below the minimum recommended level, it may indicate a circulation issue or a problem with the pool pump.
6. Check for Leaks: While testing the water pressure, inspect the heater and the surrounding plumbing connections for any signs of leaks. Leaks can lead to reduced water pressure and affect the heater's performance.

The purpose of the pressure switch is to verify the pool pump is operating properly and water pressure is present in the heating chamber. When water pressure is not present, the heater control system is designed to not allow initiation of flame. The pressure switch is preset at the factory for deck level installations. When the heater is located below the level of the spa or pool, the pressure switch may require an adjustment to compensate for the no-flow static head.

CAUTION: The Hayward Pool Heater is essentially a furnace. A trained technician should be consulted to repair it. DO NOT OPERATE the Hayward Pool Heater without a properly functioning and calibrated water pressure switch. The pressure switch adjustment requires both the pool pump and the heater be operational. As a result, extreme caution should be used during this procedure since sources of energy can not be isolated during the procedure.

The following procedure is recommended to calibrate the pressure switch.

1. The water pressure switch is located behind the front service panel. The pressure switch is typically on the left side, above the burners.
2. Be sure the water filter is clean before making the adjustment.
3. With the pump and heater system switch on, carefully turn the pressure switch adjustment dial clockwise, until a click is heard from the gas valve.
4. Turn the adjustment dial counterclockwise 1/4 turn.
5. Turn the pump off and on several times. The heater should shut off immediately when the pump is shut off. If the heater fails to shut down when the pump is off, repeat the steps above until the pressure switch is properly adjusted.
6. If the adjustment process fails to produce proper results the pressure switch should be replaced.

Before you do anything, check with Hayward as to the minimum flow they require to maintain safe temperatures in the heater. You may have to throttle the heater back. They may have a lower value pressure switch you could use, too.

Adjust the switch fully in the opposite direction. If you are at 1.5 you are at the light end of the adjustment range of that switch, which can be adjusted up to 5psi. Then let it back off until it works reliably. Rarely do you need to adjust a pressure switch on an above ground pool so it should end up about in the middle of the adjustment scale.

There is a thermistor temperature sensor beside the inlet union on the heater that goes bad, it looks line a stainless steel nut with wires on it. You can unthread to replace it and it plugs into the board behind the display. The LO means low pressure probably caused by pressure switch adjustment.

possibly poor pilot adjustment or insuficient mv output from thermopile

Low Flow errors are not necessarily real. They can be caused by improper adjustment or a defect of the pressure switch. Locate the pressure switch. Verify that the "switch" makes contact. Adjust the dial, reducing the distance the switch has to travel to engage. This will effectively lower the operating pressure required to operate. Keep adjusting until the unit stays on.

Is the heater installed indoors?? if so you'll need a vent pressure orifice kit.
if not check your water press. (below 18 PSI on filter) Place filter on "recir" if it fires and stays on . it's the pressure.
check to see if all connections a set tight hi-ltd switch wire harness etc.