Main boiler fault code E385, which may also be shown as 165, is listed by Baxi as “Under voltage”. The boiler has detected that its electrical supply voltage is below the level it expects, so it may stop operating to protect its controls and prevent unreliable operation.
This is not a water-pressure code, and it does not mean the boiler needs repressurising. It also does not prove that one particular boiler component has failed. The incoming supply, the local electrical connection and the appliance all need to be considered before the cause can be confirmed.
What does Main E385 or 165 mean?
A modern gas boiler relies on electricity to run its controls, pump, fan, sensors and ignition sequence. Voltage is the electrical pressure that allows those components to operate. UK domestic electricity is nominally supplied at 230 volts, but the code does not tell you the exact voltage measured or why the boiler considers it too low.
When an applicable Main boiler displays E385 / 165, its controls have detected an undervoltage condition. Rather than continuing with an inadequate or unstable supply, the boiler can lock out.
The code is a starting point, not a complete answer. It cannot distinguish on its own between a temporary supply dip, a local connection issue, a problem elsewhere in the property or an appliance-side electrical fault.
Which Main boilers can display E385?
Baxi’s current error-code table places E385 / 165 in the group that includes:
- Main Eco Compact Combi
- Main Eco Compact System
Main has produced other boiler ranges with different controls and displays. Always check the complete model name on the boiler or its paperwork before applying advice for an Eco Compact model.
Current official information for these boilers appears on Baxi’s website because the established Main range has been brought under the Baxi name.
Is E385 the same as low boiler pressure?
No. The word “voltage” refers to electricity. Low boiler pressure refers to the water pressure inside the sealed heating system, normally shown in bar on a gauge or display.
Baxi lists E430 / 166 as a temporary water-pressure fault. It lists E385 / 165 separately as undervoltage. Adding water to the heating system is therefore not a response to E385 unless the boiler independently shows that its system pressure is low and the exact user guide says topping up is appropriate.
Is E385 the same as E317?
No. E317 / 162 refers to the wrong electrical frequency, measured in hertz. E385 / 165 concerns voltage. They are both electrical-supply-related codes, but they describe different characteristics and should not be treated as interchangeable.
What can you check safely?
Useful checks are limited to observation:
- Photograph the full display and note whether it shows E385, 165 or both.
- Confirm the exact Main boiler model.
- Note whether the fault followed a power cut, flickering lights or electrical work.
- Check whether other appliances or lights are behaving unusually.
- Record whether the boiler loses power completely, restarts or remains locked out.
- Note whether the fault affects heating, hot water or both.
If the correct user guide permits a reset, one reset may be reasonable after a brief, isolated power interruption. Do not keep resetting or switching the boiler on and off if E385 returns.
What should you not do?
Do not remove the boiler casing, open the fused connection unit or consumer unit, test live terminals, change wiring or fit a different fuse. Do not run the boiler from an extension lead, generator, voltage converter or improvised supply.
Do not order a control board or another electrical part from the code alone. An undervoltage message describes a condition detected by the boiler; it does not identify a guaranteed failed part.
Could a power cut or supply dip cause it?
A fault may appear around a power interruption or when the supply is restored. Note the timing, because it can help the person attending. A one-off event and a code that repeatedly returns are not the same situation.
If lights are repeatedly dimming, several appliances are affected or the whole property is experiencing power problems, seek advice from the local electricity network operator or a qualified electrician. Report those symptoms when booking the boiler repair so the wider context is clear.
What happens during a repair?
The engineer will confirm the model and stored fault information, ask when the code appeared and establish whether the problem is isolated to the boiler. Appropriate checks can then be made to the supply reaching the appliance, the relevant connections and the boiler controls.
The evidence will show whether the repair belongs within the boiler, the property’s electrical installation or the incoming supply. Testing before replacing parts avoids unnecessary expense and helps ensure the fault is fixed rather than temporarily hidden.
Can I use the boiler if E385 disappears?
If a permitted reset clears the display and the boiler operates normally, keep a record of what happened. A recurring undervoltage code still needs attention, even if the appliance works between lockouts.
Do not repeatedly force a boiler to run when its controls are reporting an inadequate electrical supply. If heating is unavailable, use temporary electric heaters only as instructed, keep them clear of soft furnishings and avoid overloading sockets.
When is immediate action needed?
If you smell burning, see scorching, hear crackling from an electrical accessory or the power behaves dangerously, switch away only if it is safe to do so and contact the appropriate electrical emergency service. Do not touch damaged equipment.
Separately, if you smell gas or suspect carbon monoxide, move to fresh air and call the National Gas Emergency Service on 0800 111 999. Seek medical help if anyone has headache, dizziness, nausea, breathlessness or other symptoms.
What should I provide when booking?
Send a clear photo of the boiler display, the model name and a brief timeline. Mention power cuts, dimming lights, recent electrical work and whether other appliances were affected. There is no need to open the boiler or any electrical equipment.
Get your Main boiler back to reliable operation.
Book a fixed-price boiler repair so the E385 fault can be checked safely and the correct work carried out to fix it.
Main E385 FAQs
Are E385 and 165 the same fault?
On the applicable Main Eco Compact boilers in Baxi’s current table, E385 / 165 are listed together as undervoltage.
Should I top up the boiler?
Not for E385. This code concerns electrical voltage, not heating-system water pressure.
Does E385 mean the boiler PCB is faulty?
No. The code does not prove any single component has failed. The supply, connections and controls need to be checked.
Can I measure the voltage myself?
No live electrical testing should be attempted by a homeowner. Record the code and any wider power symptoms, then arrange professional attention.