Error 118

Safety precautions:

- Only attempt basic checks and repressurising if you are comfortable and confident. If in doubt call a Gas Safe engineer.

- Turn the boiler off and allow it to cool before doing any work around pipework or valves.

- Do not force seized valves or fittings. If something will not move, stop and get a professional.

- Watch out for escaping hot water if the system is hot; repressurise when the system is cold where possible.

Initial checks homeowners can do:

1. Look at the pressure gauge on the boiler. If it is below 1.0 bar (often near 0.5 bar or lower) that explains E118. Note the reading when the system is cold; pressure rises when hot.

2. Inspect visible pipework, radiators, radiator valves and underneath the boiler for any signs of leaks or dripping water.

3. Check whether you or someone has recently bled radiators or had work done that would have drained the system.

4. Locate the filling loop: typically a flexible braided hose or pair of small valves under or near the boiler with two handles (often blue/black). If you cannot find it or it looks non-standard, stop and get a professional.

Specific diagnostic and fix steps (repressurising):

1. Ensure the boiler is off and cold. Put the boiler in standby or off at the mains if you prefer.

2. Check the pressure gauge baseline (cold reading). Aim to top up to about 1.0–1.5 bar when cold. Do not exceed about 1.5–2.0 bar.

3. If your filling loop has two isolation valves or levers, open them slowly (usually turn or lift) to allow mains cold water into the central heating system. You will hear water flow. If it is a hose with a single valve, open it slowly.

4. Watch the pressure gauge and stop when the needle reaches between 1.0 and 1.5 bar. Close both valves fully to isolate the mains and prevent over-pressurising. If the filling loop is removable, secure it back in place according to the manual.

5. Wipe any water away and check that no visible leaks are present after filling. Re-check radiators and pipework for drips.

6. Reset the boiler following the manufacturer instructions (reset button or switch off and back on). The E118 should clear and the boiler should resume normal operation.

What to check after repressurising:

- Monitor pressure for the next 24–72 hours. Small drops can be normal after topping up, but the pressure should stabilise.

- If pressure falls again quickly, or you see water leaking from radiators, valves, or the PRV discharge pipe, shut down the boiler and call a professional.

- If the filling loop valves are stiff, broken, or you cannot form a watertight connection, do not force repairs yourself.

When to call a professional:

- The E118 error returns after you repressurise and the pressure keeps dropping.

- You find visible leaks, dripping, pooling water, or the pressure relief (discharge) pipe is continuously releasing water.

- You suspect the expansion vessel, pressure relief valve, or a pressure sensor is faulty, or the boiler will not reset.

- You are not comfortable performing the repressurising steps safely.

In these cases contact a Gas Safe registered engineer to diagnose and repair the root cause. Do not attempt internal boiler repairs yourself.