Error 117

Safety precautions:

1) If you smell gas, see a leak, or there is uncontrolled water discharge, switch off the boiler at the mains, isolate the gas supply (if you know how), turn off the system isolating valves and call Gas Safe immediately. Do not attempt internal repairs.

2) If there is water coming from the PRV or visible leaks, keep electrical components dry and isolate power to the boiler before working near it.

3) Never open sealed components, the heat exchanger, gas valve or CB connections unless you are a qualified engineer.

Initial checks a homeowner can safely perform:

1) Read the pressure: check the analogue pressure gauge (usually bottom left of the boiler casing) and the digital pressure readout. On many Atag units you can display water pressure via the control menu (press and hold Eco for ~6 seconds and scroll to A6 on iC/iS displays). Note the value.

2) Is the displayed/dial pressure greater than 3.0 bar? If yes, confirm the reading on both analogue and digital. If they disagree significantly, suspect a sensor fault.

3) Check filling loop taps: ensure the external filling loop (if used) is fully closed. An open filling loop will over-pressurise the system.

4) Look at the PRV discharge pipe (usually a plastic pipe to a safe drain). Is it discharging water now or recently? Continuous discharge indicates the PRV is operating or leaking.

5) Inspect radiators and visible pipework for leaks.

Diagnostic and simple remedial steps you can try:

1) Reduce pressure by bleeding a radiator: With the heating off and the system cold, use a radiator bleed key to let a small amount of water out at a high radiator (normally start with a downstairs radiator). Watch the boiler pressure gauge and stop bleeding once the pressure falls to the normal cold range (typically around 1.0–1.5 bar; avoid dropping below ~0.8–1.0 bar). Collect water and protect flooring. If bleeding brings pressure below 3 bar and the fault clears, monitor whether pressure rises again when the heating is turned on.

2) If the filling loop was left open, close it fully and re-check pressure. If you must lower pressure immediately and cannot bleed radiators safely, turn the boiler off and call an engineer.

3) Reset the boiler: once pressure is in the normal range, try a boiler reset (switch off for 30 seconds and restart or use the manufacturer reset procedure). If the fault clears and stays cleared, monitor the system for recurrence.

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

1) The boiler still shows error 117 after you have reduced pressure to the normal cold range and performed a reset.

2) The pressure drops or rises abnormally when the system is heated (for example pressure rises rapidly when the boiler runs) — this commonly indicates a failed expansion vessel or serviceable component.

3) The PRV is discharging or leaking, or you have visible leaks around the boiler or system pipework.

4) The analogue gauge and digital display disagree significantly, suggesting a bad sensor, wiring or PCB fault.

5) You are not comfortable performing the radiator bleeding step, or you cannot locate/operate the filling loop and valves safely.

What an engineer will check and fix (for your information):

- Confirm static and dynamic pressure readings and verify whether the pressure sensor and wiring are functioning.

- Test the expansion vessel pre-charge and, if required, re-pressurise or replace the expansion vessel.

- Inspect and replace a leaking or stuck pressure relief valve (PRV) if necessary and repair any discharged water damage.

- Check pump operation, any zone valves and for system blockages that could cause excessive pump pressure rise.

- Check filling loop operation and close/replace as needed, check for additional expansion vessels or incorrectly isolated vessels.

- Replace faulty pressure sensors or control electronics if proven defective.

Final notes:

- Do not attempt to replace the expansion vessel, PRV, pump internals, pressure sensor or PCB yourself unless you are a qualified Gas Safe engineer. These are pressurised and gas-connected components requiring specialist skills and tools.

- After any corrective work have the engineer run the boiler under heat demand and verify the system holds pressure and there is no PRV discharge. If the fault persists, arrange immediate professional service.