Overview
E317 on Potterton Assure (and related Promax/Ultra) boilers means the boiler has detected an incorrect mains electrical frequency (Hz) or believes the supply frequency is wrong. Potterton boilers are designed to run from the local mains frequency (typically 50 Hz in the UK/Ireland). The control electronics monitor the incoming AC frequency; if the sensed frequency is outside expected limits the boiler will lock out and display E317 to protect internal electronics and combustion safety systems. This fault most commonly arises if the property is temporarily or permanently being fed from a non-standard supply source (for example a generator, inverter, UPS or a foreign mains supply at 60 Hz), if there has been recent electrical work or a wrong replacement PCB/part fitted, or if the boiler’s control board or its frequency-sensing circuitry is faulty. Severity is moderate to high: running a boiler from the wrong frequency or with unstable supply can damage the PCB, cause incorrect control behaviour, or lead to unsafe operation, so the boiler locks out as a precaution. While you can perform a few safe checks yourself, accurately diagnosing mains frequency and repairing PCB/electrical faults requires a qualified electrician and a Gas Safe registered heating engineer. Do not run the boiler if you suspect the supply frequency is wrong.
Possible Cause: Wrong power supply (HZ)
Troubleshooting Steps
Safety precautions:
1. If E317 is showing, switch the boiler off at the mains isolator and do not attempt to run the boiler until the cause is determined.
2. Do not remove sealed covers or attempt internal electrical repairs. Working on gas or mains electricity must only be done by qualified engineers.
3. If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number.
Initial checks a homeowner can do:
1. Confirm whether the house is on normal mains supply or a temporary/alternative source (generator, inverter, UPS). If you are on an emergency generator or a supply fed through an inverter, that is a likely cause.
2. Check whether neighbours are without power or using the same supply — if they have normal mains, your supply is likely normal as well.
3. Ask if any recent electrical work, new consumer unit, or new boiler PCB/component replacement has been carried out. If new parts were fitted, ensure they are correct for your region.
4. Try a simple power reset: switch the boiler off at the isolator, wait 30–60 seconds, then turn it back on. Note whether E317 immediately returns or whether the boiler attempts to run. If it clears and returns, record when it happens.
Specific diagnostic and fix steps (to be carried out by qualified people):
1. Qualified electrician: measure mains frequency and voltage at the consumer unit and at the boiler supply using appropriate test equipment (true-rms meter or frequency meter). The expected mains frequency in the UK/Ireland is ~50 Hz; any sustained deviation or presence of 60 Hz indicates an issue with the supply or a connected inverter/generator.
2. Qualified electrician: check for the presence of an inverter/UPS/generator in the supply chain, and any automatic transfer switches. If an inverter is being used, confirm it provides a true sine wave at the correct frequency and voltage for the boiler.
3. Qualified engineer (Gas Safe): inspect the boiler’s PCB and power supply board for visible damage, incorrect part numbers, or poor connections. Confirm the control board fitted is the correct regional variant and firmware for 50 Hz operation.
4. Qualified engineer: check the boiler’s internal transformer or on-board frequency sensing circuit; test whether the board is falsely reporting incorrect frequency due to internal fault. If PCB is faulty, replacement by a Gas Safe engineer is required.
5. If the frequency and voltage at the mains are correct, proceed to isolate and test the boiler supply wiring and earth connections to rule out noise or interference causing misreading. Some power quality issues (severe harmonic distortion or unstable frequency) will need the electricity supplier or an electrical contractor to resolve.
6. After any repair or replacement, the engineer should clear the fault code, run the boiler through a safe start and check stable operation under load, then monitor for recurrence.
When to call a professional:
1. If the fault does not clear after a safe power reset, or if you discover you are on generator/inverter supply, switch the boiler off and contact a Gas Safe registered engineer and a qualified electrician.
2. Any inspection or replacement of the PCB, internal wiring, gas components or mains power equipment must be done by qualified personnel only.
Notes and precautions:
1. Do not operate the boiler continuously if you suspect incorrect frequency — leave it isolated until a professional confirms the supply is suitable.
2. Record the fault code, when it occurred, and any recent electrical changes or temporary power sources — this information will help the engineer diagnose the issue faster.
3. E317 specifically points to a power-frequency issue rather than a simple sensor or pressure problem; expect electrical-level tests rather than basic plumbing fixes.
In summary: perform safe initial checks and a reset, but do not open the boiler or attempt electrical repairs. Call a qualified electrician to verify mains frequency and a Gas Safe registered heating engineer to check and repair or replace boiler electronics if needed.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Assure Combi and system.