Error E117

Safety precautions:

- If the boiler has been running, turn it off and allow it to cool before working on the system to avoid scalding.

- Switch off electrical power to the boiler at the isolator before touching any controls.

- Do not try to service gas components or internal safety devices yourself — call a Gas Safe registered engineer for any gas, PRV, expansion vessel or PCB work.

- Protect floors and surfaces from water when bleeding radiators or draining the system; use towels and a container.

Initial checks a homeowner can do:

1. Note the exact error and the pressure reading on the boiler pressure gauge. Take a photo if possible.

2. Check the filling loop (flexible hose or fixed connector under the boiler). Ensure both filling loop valves are fully closed. If the filling loop has been used recently it may have been left open, raising pressure.

3. Look for signs of a leak or water discharge from the condensate/PRV pipe (usually a plastic pipe running to outside or a drain). If water is flowing from that pipe you must isolate the boiler and call an engineer.

4. If pressure is only slightly high and no discharge is visible, you can try to reduce pressure by bleeding radiators.

Step-by-step to reduce pressure by bleeding radiators (homeowner-friendly):

1. With the boiler turned off and cool, check the boiler pressure gauge. Target working pressure is normally around 1.0–1.5 bar for most systems; your manual may state the exact preferred pressure.

2. Choose a radiator at the lowest point of the system (this helps drain more water). Have a radiator key, rag and a shallow container ready.

3. Insert the radiator key into the bleed valve (usually a square or slotted valve at the top corner). Slowly open the valve a fraction of a turn until air hisses out. When water begins to come out steadily, close the valve. Catch spilt water and re-check the boiler pressure gauge.

4. Repeat bleeding other radiators as necessary until the pressure drops into the normal range. Do not over-bleed; stop when pressure is acceptable.

5. If the pressure comes down, clear the E117 error by resetting the boiler per the user manual (typically a reset button) and observe operation.

If bleeding radiators does not lower pressure or pressure quickly returns to high after reduction:

- Ensure the filling loop is definitely closed. If it is closed but the pressure rises, the auto-fill valve or filling loop non-return valve may be faulty or stuck.

- Inspect the PRV discharge pipe: persistent dripping or recent discharge indicates the PRV is operating (letting water out) and either the system is genuinely over-pressurised repeatedly or the PRV itself has failed.

- A likely cause if pressure repeatedly rises is a failed expansion vessel (loss of air charge) or a fault with the auto-fill valve. Both require an engineer: the expansion vessel must be tested and recharged or replaced by a competent engineer.

When to call a professional and what to tell them:

- Call a Gas Safe registered engineer if the boiler won’t reset after pressure correction, if the pressure stays above safe limits, if the PRV is discharging water, if the filling loop appears faulty or stuck, or if you suspect a sensor/electrical fault.

- When you call, report: the E117 code, the pressure readings you saw, whether you closed the filling loop, whether you bled radiators and what happened, and whether there is visible discharge from the PRV pipe. Provide photos if possible.

Important final notes:

- Do not attempt to replace the pressure relief valve, expansion vessel, pressure sensor or any gas-carrying components yourself. These parts involve sealed pressure systems and gas safety and must be handled by a qualified Gas Safe engineer.

- If the boiler is actively leaking from the PRV or you smell gas, isolate the gas supply, switch the appliance off, leave the property, and call the gas emergency number and a Gas Safe engineer immediately.