Error E118

Safety precautions:

1. Switch the boiler off and allow the system to cool completely before doing any work. Topping up when the system is hot can give a misleading pressure reading and risks scalding.

2. Do not tamper with gas valves, the burner, or internal controls. If you are not confident, stop and call a Gas Safe engineer.

3. Work in a dry area and have towels or a container ready in case a small amount of water escapes while using the filling loop.

Initial checks a homeowner can do:

1. Look at the pressure gauge on the front of the boiler. If it reads below about 1.0 bar (or is in the red/near zero) that confirms low pressure.

2. Check visible pipework, radiators, valves, and the area beneath the boiler for signs of dripping or pooling water. Also check radiator bleed points and valves for weeps.

3. If you recently bled radiators or had plumbing work done, that commonly explains a drop in pressure.

Specific diagnostic and fix steps (repressurising the system):

1. Locate the filling loop: on many Baxi models it is under the boiler as an integral loop with two quarter-turn valves (often blue) or an external braided hose with two taps/black handles. The filling loop connects the cold mains to the heating system.

2. Ensure the boiler is off and cold. Identify the cold water isolation valve and the two filling loop valves. Do not touch gas pipes or black gas valves at the back of the boiler.

3. Open the filling loop valves slowly and carefully (usually turn a quarter-turn so they sit inline with the pipe) and listen for water flowing into the system. Watch the pressure gauge as you do this.

4. Stop adding water as the needle reaches the target range: typically 1.0–1.5 bar when the system is cold (1.5 bar is commonly recommended on many Baxi guides). Do not over-pressurise — higher pressure may be hard to remove and can trigger other safety devices.

5. Close both filling loop valves fully to isolate the mains from the heating system. If your filling loop is an external braided hose with screws or taps, return them to the closed position.

6. If you had to open a cold isolation valve earlier, return it to its original position.

7. Turn the boiler back on and reset the fault per the boiler instructions (use the reset button or control panel). The E118 code should clear and the boiler should fire if there are no other faults.

8. Once the system heats, re-check the pressure when cold again after a short run cycle. Some expansion and temperature changes can alter pressure; if pressure rises too high when hot or drops significantly after cooling, note that and inform a professional.

Further checks and what to watch for:

1. If the pressure drops again within a few days or rapidly after repressurising, you likely have a leak, a faulty pressure relief valve (PRV), or a problem with the expansion vessel. Look for damp patches, staining, or radiator valves weeping. Check the PRV discharge pipe for signs of water discharge.

2. If you cannot get pressure to rise when using the filling loop, or if you see water escaping when operating the loop, stop and call a qualified engineer.

3. If the E118 persists after you have correctly repressurised and reset, or you find evidence of leakage, arrange a Gas Safe registered engineer to inspect the system. Repeated pressure loss, a leaking PRV, or a suspected failing expansion vessel require professional diagnosis and repair.

When to call a professional:

Call a Gas Safe registered engineer if you are unsure about any step, if the filling loop is not obvious, if the pressure keeps dropping after repressurising, if you find a leak you cannot repair, if the PRV is discharging, or if the boiler still shows E118 after correct repressurisation and reset. Working on gas appliances and internal hydraulic faults should be left to qualified engineers for safety and compliance.