Sta-Rite Max-E-Therm Automatic Gas Shut Off Switch, 42002-0025S

This is the Sta-Rite 42002-0025S automatic gas shut off switch, a new OEM part for the Max-E-Therm line of pool heaters. It is listed for the SR-200, SR-333 and SR-400.

What it does

The switch is a safety device on the gas side of the heater. If operating conditions move outside the safe range, it cuts the gas instead of letting the burner continue. That is why a failed switch usually shows up as a heater that will not fire rather than as a heater that runs badly.

Where it sits

It is part of the Max-E-Therm electrical system group, along with the thermistor, transformer, ignition control module and air flow switch. The same switch is also carried under Pentair MasterTemp heater electrical system parts, so if your heater is a MasterTemp, check the part against your own diagram before ordering.

Before you replace it

Several parts in this group can stop a heater from lighting. Run the heater diagnostics first so you are replacing the part that actually failed rather than working through the group one item at a time.