Honeywell L404F1243 Pressuretrol Controller

The Honeywell L404F1243 Pressuretrol Controller is an automatic-recycle pressure control from the L404F series, built to start and stop a burner or switch a control circuit as boiler pressure rises and falls. This model covers an adjustable range of 5 to 50 PSI with an adjustable 6 to 14 PSI differential, and it connects to the pressure source through a 1/4" NPT internal-thread fitting on the diaphragm. The switch is a snap-acting SPDT (single-pole, double-throw) design: when pressure rises to the setpoint the R-W contacts make and the R-B contacts break, and both flip back as pressure falls by the differential. It is a line-voltage control rated for 120/240 Vac.

Understanding how the L404F1243 works makes setup and troubleshooting much easier. System pressure acts on the diaphragm behind the hex fitting, and that force is balanced against a calibrated spring you set with the main scale adjusting screw on top of the case. The differential adjusting screw sets how far pressure must fall below the setpoint before the switch recycles. Because the L404F uses a subtractive differential, the differential is subtracted from the main scale setting, so a 15 PSI setpoint with a 6 PSI differential recycles at roughly 9 PSI. The contacts are rated 8.0 amps full-load at 120 Vac and 5.1 amps full-load at 240 Vac, so use a relay or contactor for larger loads. Honeywell also builds the L404F in 2-15 PSI, 10-150 PSI and 20-300 PSI ranges, which are different controls from this 5-50 PSI model.

On steam service, always pipe the L404F1243 through a siphon loop (pigtail) so a cushion of condensate, not live steam, sits against the diaphragm. After setting the main scale, confirm the actual cut-out with a test gauge on the same boiler, because the printed scale is a guide and not a substitute for a gauge. Typical failure signs are short-cycling from a differential set too tight or a plugged siphon, a burner that will not fire from burned or open R-W contacts, and pressure climbing past the setpoint from welded contacts. With power off, meter continuity across R-W and R-B while you raise and lower pressure; they should swap at the setpoint. Replace it with a control of the same 5-50 PSI range and auto-recycle action, never a manual-reset limit, and keep the boiler's separate high-limit and safety relief valve in place as code requires.

Key Benefits

• Auto-Recycle Operation: The L404F1243 resets itself when pressure falls by the differential, so the boiler cycles automatically without a manual reset.
• 5-50 PSI Adjustable Range: One control covers the common low-pressure and medium-pressure steam boiler setpoints with a main scale you can set on site.
• 6-14 PSI Adjustable Differential: The differential adjusting screw lets you widen the cycle to reduce short-cycling or tighten it for steadier pressure.
• SPDT Snap-Acting Switch: The R-W make and R-B break contacts give crisp switching and let a single control change over between two circuits.

Common Questions

• What does auto recycle mean? The contacts reset on their own once pressure drops by the differential. A manual-reset control stays tripped until someone presses a button, so the two are not interchangeable.
• What pressure range and differential does the L404F1243 cover? The L404F1243 is a 5 to 50 PSI control with an adjustable 6 to 14 PSI differential, set with the main scale and differential screws.
• How is it connected? Pipe it to the boiler through a siphon loop using the 1/4" NPT fitting, then wire it to the burner circuit at 120/240 Vac using the R, W and B terminals.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.