Baxi E385 fault codewhat it means and how to fix it
Under-voltage (shown on some boards as 165): the supply at the board dropped below what it will run on. Usually a house-wiring or supply problem the boiler is reporting, not causing.
Take care
Get a Gas Safe registered engineer to look at your Baxi E385
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What E385 means
E385 is listed on Baxi's professional page as "E385 / 165 — Under voltage", the 165 being the alternative number some boards in the family display. The board monitors the mains it is fed and will not run the burner if the voltage falls below its threshold, because the gas valve, the fan and the ignition transformer all need a supply within range to behave predictably. It is the boiler's way of protecting itself from a brownout.
What makes E385 useful rather than alarming is that it points away from the boiler. A supply that sags at the boiler terminals is sagging because of the house wiring — a long, thin spur, a loose connection in the fused spur or the consumer unit, a shared circuit that dips when a heavy appliance starts — or because the incoming supply itself is low, which other appliances in the house will also show. The board is only the culprit when a genuinely good supply is being read as low, which is a measurement fault.
E385 does not appear in the 600 and 800 manuals' printed table or their list of codes that relight from the Reset button; this page rests on the professional table's listing for the family, and where it shows it carries the spanner symbol, so the user guide's instruction is to contact your installer or Baxi Customer Support. A pattern to notice: E385 that arrives in the evening, or when the shower or the oven is on, is a house-wiring problem and wants an electrician as much as a heating engineer.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Loose or high-resistance connection | At the fused spur, the boiler terminal strip or the consumer unit. A connection that heats and drops volts under load, so the boiler sees a supply that falls when other things are on. | Common |
| Supply genuinely low | A rural or end-of-line property where the incoming voltage sits low, made worse at peak times. Other appliances dim or misbehave at the same moments. | Occasional |
| Shared circuit with a heavy load | A boiler on a circuit that also feeds a shower, oven or tumble dryer sees a dip each time the load starts. The code is intermittent and follows the pattern of use. | Occasional |
| PCB measurement fault | The board reads a good supply as low. Concluded only after the supply has been measured at the boiler terminals under load. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£400
Time on site
45 minutes
Supply check and terminal tightening £80–£150. Electrical repair to a spur or circuit £100–£250. PCB, if the supply is proven good, £250–£400.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
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Baxi / Potterton / Main main PCB
£150–£320Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Baxi fault codes
- E168Get it checkedTrade lists call E168 a Baxi PCB lockout, but no Baxi UK manual or error-code page prints it. Treat it as a board fault: one power cycle, then an engineer.Related: electronics and power
- E83Usually simple to fixE83 to E87: the boiler has lost contact with a connected control — a room unit or programmer wired to the board. Check the control first; the boiler itself is usually fine.Related: electronics and power
- E103Get it checkedSafety Assist codes E103, E104 and E107: the battery-backed safety board on the 600 and 800 is exhausted, faulty or out of step with the main board. Contact your installer; there is no reset.Related: electronics and power
- E.02.47Usually simple to fix"Connection to external device unsuccessful": a Baxi 200/400 Combi or Combi 2 has lost a control it was paired with. Check the control and its wiring; Baxi's remedy is the auto-detect function.Related: electronics and power
- E55Get it checked"Calibration Required": the gas valve has not been set up to the board after a PCB or valve change. An engineer's combustion-analyser job, not a fault a householder can clear.Related: electronics and power
- E317Get it checkedMains frequency out of range (shown on some boards as 162). The boiler, not the supply, is almost always the odd one out. Check other appliances, then call an engineer.Related: electronics and power
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer support portal
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.