Error 1P4

Safety precautions:

1. If you are unsure about working on a gas appliance, stop and call a Gas Safe registered engineer.

2. Turn off the boiler and set any thermostats or timers to off/standby so the heating does not try to run while you work. Allow the system to cool so you are reading cold pressure and to avoid hot water burns.

3. Wear gloves and eye protection if you will be handling valves or bleeding radiators. Do not force or overtighten any fittings.

Initial checks homeowners can do:

1. Look at the boiler display (top right of the control display when a fault shows) or the analogue pressure gauge (often under the bottom-left of the boiler) and note the pressure reading. 1P4 means pressure is low (approx 0.5–0.8 bar).

2. Visually inspect visible pipework, the boiler base, and radiators for signs of leaks, damp patches, or dripping. If you find a leak, do not try to repressurise — call a Gas Safe engineer.

3. Check radiators for cold spots or a recent need to bleed radiators (bleeding will reduce pressure). If you recently bled many radiators, re-pressurising is expected.

Specific diagnostic and fix steps (re-pressurising using the filling loop):

1. Locate the filling loop: on iC / iC Economiser Plus models it is usually a removable copper 'U' shaped tube that connects between a small blue and a black isolation valve under the boiler. On some iS models it may be an external flexible braided hose. If you cannot find the filling loop, consult the boiler handbook or call an engineer.

2. Ensure the boiler is off and the system is cold. Remove any protective caps on the two filling valves. If a removable loop is provided, fit the loop into the two valve connections and finger-tighten the nuts only — do not use tools to over-tighten.

3. Open the valves slowly: usually turn the black tap a quarter turn towards you first, then slowly open the blue tap a quarter turn towards you. You should hear water entering the system. Watch the digital display or gauge as the pressure rises.

4. Target pressure: increase cold system pressure to around 1.0–1.1 bar (some documentation states up to 1.2 bar is acceptable). Do NOT overfill past 1.4 bar. When the correct pressure is reached, close the blue valve first, then the black valve.

5. Remove the filling loop (if removable) and replace the protective caps. Leave the loop removed unless instructions say otherwise. Tighten nuts by hand only when refitting caps.

6. Return the boiler to normal operation. The 1P4 error should clear and the normal home screen with temperatures and pressure should reappear. Allow the system a few minutes; some boilers run an automatic air purge cycle after filling.

If you overfill the system:

1. If the pressure is too high (error 109 or pressure reading above safe range), bleed water from a radiator until the pressure falls below about 1.2 bar (ideally to around 1.0–1.1 bar when cold).

When to call a professional (must-call situations):

1. The fault does not clear after repressurising or you cannot raise the pressure to the required level.

2. The system loses pressure again soon after filling or you must top up frequently — this usually means a leak or a faulty component (expansion vessel, pressure relief valve, pipework) that needs a professional diagnosis.

3. You find visible leaks, dripping from the boiler, or damaged pipework.

4. You cannot locate or safely use the filling loop, or you spot unusual noises, smells, or error codes alongside 1P4.

Notes and cautions:

1. Follow the boiler manufacturer’s manual for your exact model; locations and procedures vary slightly between iC, iS and other ranges. Some models provide a digital pressure readout in a specific menu (e.g., holding Eco for several seconds and checking A6) — consult the manual if needed.

2. If in doubt, or if any repair beyond repressurising is required, contact a Gas Safe registered engineer or ATAG support (contact details are in the manual) rather than attempting gas or sealed system repairs yourself.