Proof of Closure connections on J18, Pins 2 and 3 are open
The Closure Switch fault error code on Weil-Mclain boilers indicates proof of closure connections on j18, pins 2 and 3 are open.
Weil-Mclain Closure Switch fault means: proof of closure connections on j18, pins 2 and 3 are open. The usual cause is proof of closure connections on j18, pins 2 and 3 are open. You can safely reset the boiler once — if Closure Switch fault returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does Closure Switch fault Mean
The Closure Switch fault code is shown by the boiler’s control board when it detects proof of closure connections on j18, pins 2 and 3 are open. 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 Closure Switch fault and the boiler stops until the fault is cleared |
Common Causes
Causes documented in the Weil-Mclain service literature published by weil-mclain.com, cross-checked against the manufacturer’s fault-code table.
| Cause |
|---|
| Proof of Closure connections on J18, Pins 2 and 3 are open |
Safety Warning
Closure Switch fault 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
Soft lockout for 4 minutes then unlocks and checks for up to 4 minutes If still open, soft lockout for 4 minutes Repeats once more then a manual lockout
Refer to the Weil-Mclain service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Weil-Mclain models that can display fault code Closure Switch fault:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Weil-Mclain models | — | Possible |
Frequently Asked Questions
Soft lockout for 4 minutes then unlocks and checks for up to 4 minutes If still open, soft lockout for 4 minutes Repeats once more then a manual lockout. According to the technical documentation, this is the first check on the list for Closure Switch fault.
Closure Switch fault is not classified as a high-severity fault, so the boiler can be reset once. If Closure Switch fault comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.