Error S.41

Safety precautions:

- Before doing anything, switch the boiler off at the programmer and isolate electrical power at the fused spur if accessible. Allow the boiler and system to cool to avoid scalding from hot water or steam.

- Wear eye protection and gloves when bleeding radiators or draining water. Have a bucket and cloths ready for any water removed.

- Do not attempt to work on gas, sealed hydraulic or internal boiler components beyond simple user actions (bleeding radiators, closing filling loop valves). For any internal repairs, replacement parts, or gas work, call a Gas Safe registered engineer.

Initial checks a homeowner can do:

1. Check the pressure reading on the boiler display. Confirm it is above 2.8 bar.

2. Look under the boiler and check the filling loop valves are fully closed. If the filling loop has been used recently it may have been left partly open and overfilled the system.

3. Inspect the PRV discharge pipe (usually a plastic pipe running from the boiler to a safe discharge point). Look for signs of recent discharge: dripping, staining, or water on the floor or outside. If the PRV has discharged, do not continue to operate the boiler and call an engineer.

4. Note whether the high pressure happens only when the system is hot or is high when cold. If pressure is normal cold and only goes high when hot, this suggests an expansion vessel problem.

Diagnostic and simple fix steps:

1. If the filling loop is open: ensure both filling loop isolation valves are fully closed (valve heads perpendicular to the pipe). This stops more mains water entering the system.

2. Reduce the system pressure safely by bleeding a radiator or using the system drain-off point: a. Turn the boiler off and allow the system to cool. b. Starting with a radiator near the lowest point in the system, use a radiator key to open the bleed valve slowly into a container until the boiler display falls to around 1.0–1.5 bar. c. Close the radiator bleed valve firmly. d. Re-check the boiler pressure and the display. This lowers pressure but will not fix the underlying cause if pressure rises again.

3. Reset the boiler following the manufacturer’s instructions (many models will clear the status after pressure is corrected). Monitor the system for an automatic return to normal operation.

4. If pressure drops to normal and stays stable when the system is cold and hot, the immediate issue is resolved. If pressure rises again when the system heats, or the PRV is dripping or has discharged, stop using the boiler and call a qualified engineer.

When to call a professional (must call):

- The filling loop was closed but you cannot reduce the pressure to the normal range.

- The pressure keeps rising after you reduce it (especially when heating).

- The PRV is dripping or has discharged water — this usually indicates a failing PRV or expansion vessel problem.

- You suspect the expansion vessel has lost its pre-charge (engineer needed to test and re-pressurise or replace it).

- Any signs of leaks, persistent faults, or if you are unsure what to do.

Notes and important warnings:

- Repeated overpressure events or a leaking PRV should not be ignored; they risk water damage and component failure.

- Do not attempt internal repairs to the boiler, replace the PRV, or adjust the expansion vessel air charge yourself unless you are a qualified engineer.

- If in doubt, isolate the boiler, switch it off, and contact the installer or a Gas Safe registered engineer to diagnose and repair the root cause.