Either the optional manual reset low gas pressure switch or the optional manual reset high gas pressure switch tripped
The Gas Pressure SW error code on Lochinvar boilers indicates either the optional manual reset low gas pressure switch or the optional manual reset high gas pressure switch tripped.
Lochinvar Gas Pressure SW means: either the optional manual reset low gas pressure switch or the optional manual reset high gas pressure switch tripped. On this component the documented failure modes are the gas pressure switch contacts on the, board are open or wiring, connector or harness of the pressure switch damaged or loose. You can safely reset the boiler once — if Gas Pressure SW returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does Gas Pressure SW Mean
The Gas Pressure SW code is shown by the boiler’s control board when it detects either the optional manual reset low gas pressure switch or the optional manual reset high gas pressure switch tripped. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows Gas Pressure SW and the boiler stops until the fault is cleared |
Common Causes
The first cause below is the one the Lochinvar service literature publishes for this code (source: lochinvar.com). The others are the failure modes documented for the same component on other boilers, confirmed by 4 different manufacturers.
| Cause |
|---|
| The gas pressure switch contacts on the |
| Board are open |
| Wiring, connector or harness of the pressure switch damaged or loose |
| Flue or air intake blocked or restricted |
| The pressure switch has failed — short circuit or open circuit |
| Heat exchanger fouled or partially blocked |
Safety Warning
Gas Pressure SW involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
How to Fix It
Reset the pressure switches
Measure the supply gas pressure to determine cause of failure. Natural gas pressures should be between 4 - 14 inches w.c. and LP gas pressures should be between 8 - 14 inches w.c
Refer to Section 7 - Gas Connections of the Knight Boiler Installation and Operation Manual for detailed information concerning the gas supply
Correct the supply gas pressure if necessary
Check for a loose or misplaced jumper if pressure switches are not installed
Refer to Section 4 - Gas Connections of the Outdoor Knight XL Installation and Operation Manual for detailed informati
Refer to the Lochinvar service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Lochinvar models that can display fault code Gas Pressure SW:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Lochinvar models | — | Possible |
Frequently Asked Questions
Reset the pressure switches. According to the technical documentation, this is the first check on the list for Gas Pressure SW.
Gas Pressure SW is not classified as a high-severity fault, so the boiler can be reset once. If Gas Pressure SW comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.