Baxi [E118] fault codewhat it means and how to fix it

E118 is the low-pressure code on every Baxi with a digital display and a Reset button — the 600 and 800 Combi and System, the Duo-tec 2 Combi GA, the Duo-tec, Platinum and Megaflo Compact, the Assure and the later Megaflo System. The 600 Combi installation manual defines it in one line: "118 is displayed when the primary water pressure is less than 0.5 bar", and the table entry is "Primary system water pressure too low".

The user guide for the same boiler puts E118 in its problems-and-solutions table with the remedy "Re-pressurise the system" and gives the working range as 1 to 1.5 bar cold on the dial. That is the whole of the manufacturer's position: the sealed circuit has lost water, the boiler will not fire a heat exchanger it cannot be sure is full, and the code goes when the pressure comes back.

What the manual adds for the engineer is worth knowing. The component behind the code is a hydraulic pressure switch on the 600 and 800 (Baxi part 5114748), and the fault-finding flow for E118 checks first that the system really is below 0.5 bar, then the switch wiring and a 5 V feed at connector X22 on the PCB, then replaces the switch. So a boiler showing E118 with a healthy gauge reading has a switch or wiring problem, not a leak. If you own an older selector-switch Baxi the same fault is E119, and that page explains the difference. The EcoBlue Advance user guide adds that "Error Codes 117 and 118 can be reset by restoring the correct system pressure" without pressing anything.

1. 1

   Read the pressure gauge on the front of the boiler with the system cold. Baxi's user guide wants it between 1 and 1.5 bar cold; below 0.5 bar is where E118 appears.

2. 2

   Find the filling loop. On a 600 or 800 it is usually a braided hose with a valve at each end under the boiler, though some installations use a pair of taps on the pipework or an internal keyed link.

3. 3

   Open both valves slowly and watch the gauge climb. Stop at 1 to 1.5 bar. Close both valves fully.

   Do not take it past 2.5 bar. Baxi's pressure relief valve lifts at 3 bar and will dump the excess outside, and a system that has been overfilled cold will be well over when hot.
4. 4

   E118 clears itself once the pressure is back. If the boiler still shows a code, check it is E118 and not something else, then press Reset for one to three seconds.

5. 5

   Bleed any radiators that are cold at the top, then check the gauge again and top up if needed. Note the date; if you are back here within a few weeks there is a leak or a flat expansion vessel to find.