Error E118

Safety precautions:

- Before doing anything, turn off the boiler and allow it to cool. Work in a dry area and have towels/containers ready for any drips.

- Do not tamper with gas fittings or internal boiler components unless you are a qualified Gas Safe engineer.

- Isolate the mains water if you will disconnect the filling loop after use.

Initial checks homeowners can do:

1. Check the pressure gauge on the front of the boiler. Note the reading when the system is cold. Normal is generally 1.0–1.5 bar; E118 appears when pressure is very low (often under ~0.5 bar).

2. Look for obvious leaks around radiators, pipe joints, valves, and under the boiler. Check the overflow/drain pipe for signs of recent discharge (a sign the pressure relief valve may be leaking).

3. Have you recently bled radiators, topped up, or had plumbing work done? That can explain a drop in pressure.

Specific diagnostic and fix steps (repressurise using the filling loop):

1. Locate the filling loop. It is usually a braided metal hose with two isolation valves or levers under the boiler or attached nearby. Some Baxi models have an integral lever or built-in filling valve.

2. Confirm both isolation valves on the filling loop are closed before you start.

3. Slowly open the first valve, then the second valve, allowing mains water to enter the heating system. You should hear water flow. Open slowly to avoid water hammer.

4. Watch the pressure gauge carefully as the system fills. Stop when the gauge reaches about 1.0–1.5 bar (check your boiler manual for the exact recommended cold pressure). Do not overpressurise; avoid going above 2.0–2.5 bar.

5. Close both filling loop valves fully and, if your filling loop is a removable braided hose, either leave it secure or remove and store it as per the boiler manual. Ensure valves are fully closed to prevent mains water permanently feeding the heating system.

6. Wipe up any drips and re-check around radiators and pipework for leaks. If you bled radiators earlier, you may need to repressurise again after bleeding to replace lost water.

7. Reset the boiler according to manufacturer instructions (some models will clear the error automatically once pressure is acceptable; others have a reset button). Switch the boiler on and check for normal operation and that the E118 code has cleared.

What to watch for and when to call a professional:

- If the pressure drops again within a few days or hours after repressurising, you likely have a leak or a faulty pressure-related component. Call a Gas Safe registered engineer.

- If you see water coming from the pressure relief valve discharge pipe or notice damp patches, call a professional—don’t leave the system running.

- If you are unsure where the filling loop is, the valves look different to those described, or you are uncomfortable performing the repressurisation, contact a Gas Safe engineer.

- Do not attempt to repair or replace pressure relief valves, expansion vessels, internal seals, sensors, or gas components yourself. These require a qualified engineer for safe, compliant repair.

Aftercare:

- Monitor the pressure gauge daily for a few days after topping up. Record readings and any visible leaks.

- If the E118 fault persists or returns, arrange inspection and repair by a Gas Safe registered engineer to locate leaks or faulty components and to carry out necessary repairs safely.