The FDXLBVS1930 is a genuine Hayward replacement blower vacuum switch engineered specifically for Universal H-Series pool heaters rated from 150,000 to 400,000 BTU. This safety switch monitors negative pressure (vacuum) generated by the blower to confirm proper airflow before allowing ignition -- protecting the heat exchanger and combustion chamber from damage caused by blocked or restricted venting. Also catalogued as NBK Parts number 20410K, this is a direct drop-in replacement requiring no modifications.
Pool heater vacuum switches are a common wear item and a frequent cause of ignition lockout faults. When the blower vacuum switch fails or loses calibration, the heater's control board reads insufficient airflow and refuses to light -- even when the blower motor itself is running fine. Replacing the switch with a genuine Hayward FDXLBVS1930 restores proper pressure sensing and gets the heater firing reliably again.
This switch is compatible with all 12 models in the Universal H-Series FDN (natural gas) and FDP (propane) lineup, from the H150 through the H400. If your heater displays an ignition error or AFS (air flow switch) fault code and the blower is spinning normally, this switch is the first part to inspect and replace.
FDXLBVS1930 is a factory Hayward component, also listed under NBK part number 20410K. Exact fit, no adapters or modifications needed.
Fits all H-Series models from 150,000 BTU through 400,000 BTU -- both natural gas (FDN) and propane (FDP) configurations.
Monitors blower-generated vacuum to confirm adequate combustion airflow before ignition, protecting the heat exchanger and preventing unsafe operation.
A failed vacuum switch is a leading cause of AFS fault codes on H-Series heaters. Replacing this switch often resolves no-heat calls without replacing the control board.
When the heater calls for heat, the blower motor starts first. As the blower spins up, it creates a measurable negative pressure (vacuum) in the combustion air path. The vacuum switch is a pressure-differential device wired into the ignition control circuit. Once the vacuum reaches the switch's setpoint, the contacts close, signaling the control board that airflow is confirmed and ignition can proceed.
If the switch contacts fail to close -- due to a faulty diaphragm, corroded contacts, a cracked pressure port, or a shift in calibration -- the board interprets the open circuit as an airflow fault and locks out ignition. Inspecting and replacing the FDXLBVS1930 is the correct diagnostic step before condemning the blower motor or control board.
The FDXLBVS1930 fits the following Hayward Universal H-Series pool and spa heater models:
FDN = Natural Gas configuration. FDP = Liquid Propane configuration. Both gas types use the same vacuum switch.