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

On the Assure and the Promax Ultra the low-pressure code is 118. Both installer manuals name the primary circuit's pressure as the thing that is too low, and both fix the trigger at the same point — the code comes up once the primary circuit has fallen below half a bar. It replaces E119 for owners moving from a Promax, and the number is the only thing that changed; the threshold and the remedy are the same.

What is different is how the Assure treats you afterwards. Its user guide says: "When the correct pressure is restored the boiler will reset automatically", and it wants the top-up earlier than the old boilers did — "If the water pressure is lower than 0.7 bar, the system must be topped up", with the boiler stopping at 0.5. The Assure also shows the pressure on the screen as well as on the gauge when there is power, which makes the fill easier to judge.

The user guide's repressurising section describes the same two-tap arrangement as the Promax — "a temporary filling loop consists of two isolating taps and a separate filling pipe" — and repeats the warning that "if the water pressure requires regular re-pressurising a fault or leak is indicated". The Promax Ultra adds a code the Assure does not have at the other end of the scale: 117 for pressure above 2.7 bar, which is where an over-enthusiastic top-up ends.

1. 1

   Let the boiler cool and check the pressure on the gauge or on the display. The Assure guide wants a top-up below 0.7 bar and normal running between 1 and 2 bar.

2. 2

   Locate the loop: either two isolating taps that take a separate filling pipe, or a permanent loop on the pipework near the boiler. If you have the temporary type, connect the pipe between the taps and tighten the nuts.

3. 3

   Fully open one tap, then open the second carefully while watching the gauge or the screen. Stop at 1–1.5 bar and close both taps.

   Above 3 bar the safety valve operates and the guide says to contact your installer. On a Promax Ultra you will see 117 before that, at 2.7 bar.
4. 4

   Disconnect the filling pipe (a little water will come out), refit blanking caps if you have them, and keep the pipe. The boiler restarts on its own once the pressure switch is satisfied; no button press is needed.