Baxi E317 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E317 fault code mean?
The E317 code appears when your Baxi boiler's PCB detects that the incoming mains electricity is not operating at the expected 50 Hz frequency standard used across the UK grid. Rather than continue running under potentially abnormal electrical conditions, the boiler shuts itself down as a precaution. In most cases, either the mains supply has experienced a disturbance, or the PCB itself is misreading an otherwise normal supply — the latter being the more common culprit in practice.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or degrading PCB Common
The PCB is responsible for reading and interpreting the mains frequency signal. If the board is ageing, has suffered heat stress, or has developed a component fault, it can report an incorrect frequency even when the incoming supply is perfectly normal. This is the most frequent root cause seen in practice.
- Loose or corroded internal wiring Common
Wiring connections between the mains input and the PCB can work loose over time due to vibration or thermal cycling. A poor connection can cause the PCB to receive a distorted or intermittent frequency signal, triggering the E317 lockout.
- Mains supply disturbance or power surge Sometimes
The UK grid nominally runs at 50 Hz, but local surges, nearby industrial equipment, or grid disturbances can momentarily push the frequency outside the boiler's acceptable tolerance. A one-off surge may also leave residual damage on the PCB.
- Moisture or water ingress damaging the PCB Sometimes
Even without a direct leak onto the board, humidity from a nearby internal drip can cause corrosion on PCB components over time. Corroded tracks or contacts can produce erratic frequency readings and trigger this fault.
How to fix it
- Note down the fault code and attempt a single boiler reset DIY safe
Before doing anything else, write down the E317 code. Locate the reset button on your Baxi boiler (usually marked with a flame symbol or labelled 'Reset') and hold it for a few seconds. If the boiler restarts and runs normally, monitor it over the next hour. Do not reset more than two or three times — repeated resets will not cure an underlying electrical fault and may mask the problem further.
- Check your consumer unit for tripped breakers DIY safe
Go to your fuse board (consumer unit) and check whether any circuit breakers have tripped, particularly the one supplying the boiler. If a breaker has tripped, reset it once. If it trips again immediately, there is a wiring or electrical fault that needs professional attention — do not keep resetting it.
- Check whether a power surge or outage recently occurred DIY safe
Ask neighbours or check online whether there has been a local power cut or grid disturbance. If others on your street were also affected, a temporary supply issue may have triggered the lockout. In that case a reset (as in Step 1) may be all that is needed.
- Do not attempt any internal electrical or PCB work yourself Gas Safe engineer
Opening the boiler casing and working on internal wiring, connectors, or the PCB requires specialist knowledge and carries serious risk of electric shock or further damage to the boiler. This work must only be carried out by a qualified Gas Safe registered engineer.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
If the E317 code returns after resetting, you need a professional diagnosis. An engineer will use a multimeter to measure the actual incoming mains frequency at the boiler terminals, inspect internal wiring for loose or corroded connections, and use Baxi diagnostic tools to test the PCB. This process distinguishes a genuine supply problem from a faulty board — and that distinction determines whether the fix is a wiring repair, a PCB replacement, or liaising with your energy supplier.
- PCB repair or replacement if diagnosed as the root cause Gas Safe engineer
If the PCB is confirmed as faulty, a Gas Safe engineer will advise on replacement. Full PCB replacement is typically the recommended route over repair on individual components. Before agreeing to the work, check whether your Baxi boiler is still within its warranty period — Baxi warranties can extend up to 10 years when installed by an accredited engineer and serviced annually, in which case the repair may be covered at no cost.
Parts you may need
- Baxi PCB (printed circuit board) · from £180
- Boiler wiring harness / loom · from £55
- Mains input connector block · from £20
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£450, depending on the underlying cause.
Frequently asked questions
Is the E317 fault dangerous — should I stop using the boiler immediately?
The boiler will have already locked itself out, so it is not operating. This is a protective response rather than an immediate safety emergency in the way a gas leak would be. However, you should not repeatedly override the lockout with resets and continue using the boiler as normal. Leave it locked out and arrange for an engineer to diagnose it promptly, particularly in cold weather when you cannot afford to be without heating for long.
Could the E317 just be a one-off glitch, or is it always a serious fault?
It can genuinely be a one-off. A brief grid disturbance or a power surge in your street can cause the boiler's PCB to flag an anomaly and lock out. If a single reset clears the fault and the boiler runs normally afterwards with no recurrence, it was likely a transient supply issue. However, if the E317 returns — even after a day or two — you should treat it as a persistent fault and call an engineer rather than continuing to reset it.
How much does it cost to replace a Baxi PCB in the UK?
A PCB replacement on a Baxi boiler typically costs between £300 and £500 all-in, covering the part, labour, and VAT. This is why the headline repair range for E317 sits at £150–£450: a wiring fix or call-out that finds a simple connection issue sits at the lower end, while a full PCB swap pushes toward the upper end. In rare cases where the board is hard to source or the boiler is an older model, costs can edge above £500. If your boiler is older and facing a costly PCB replacement, it is worth asking the engineer whether a new boiler would be more economical in the long run.
Will my Baxi warranty cover the E317 fault?
It may well do. New Baxi boilers come with at least a two-year manufacturer warranty, and this can extend to up to 10 years if the boiler was installed by a Baxi-accredited installer and has been serviced annually. If you are within the warranty period and have kept up with annual services, contact Baxi directly before booking an independent engineer, as the repair could be covered at no cost to you. You will need your installation paperwork and service records to hand.