Remeha E3 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E3 fault code mean?
The E3 code appears on Remeha boilers (including the Avanta range) when the boiler detects a problem with the control unit or identifies an earth fault on the electrical supply. The boiler will lock out and stop working as a safety measure. In plain terms, the boiler's electronics have either lost confidence in their own operation, found an issue with the power supply earth, or detected an anomaly from one of the temperature sensors. Because an earth fault carries a genuine electrical safety risk, this code should be treated seriously and not repeatedly reset without investigation.
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 poorly connected temperature sensor Common
The flow, return, or boiler temperature sensor may have developed a short circuit internally, or its wiring connector may have worked loose from the control board. The boiler interprets an out-of-range signal as a potential fault and locks out to protect itself.
- Low system pressure or air in the system Common
If there is insufficient water circulating — whether because system pressure has dropped below around 1 bar, or because air has built up and is blocking flow — the boiler cannot manage heat properly and may trigger an E3 as a protective measure.
- Mains supply not properly earthed Sometimes
If the electrical supply to the boiler does not have a proper earth connection, the control unit can misread voltages and flag an earth fault. This requires an NICEIC-registered electrician to investigate, not a heating engineer.
- Faulty PCB (control unit) Sometimes
If the earthing is confirmed correct and sensors check out, the control board itself may have failed. PCB failures can be caused by power surges, moisture ingress, or simply age. This is typically the diagnosis of last resort once other causes are ruled out.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when the system is cold. If it has dropped below 1 bar, use the filling loop (usually a braided hose or lever valve beneath the boiler) to top it up slowly until it reaches around 1.2 bar, then close the valve. If you are unsure how to do this, your boiler manual will have a diagram specific to your model.
- Bleed radiators to remove trapped air DIY safe
If you suspect air in the system — for example, radiators that are warm at the bottom but cold at the top — bleed them using a radiator bleed key. Work from the ground floor upwards. After bleeding, recheck the system pressure and top up again if needed.
- Reset the boiler (once or twice only) DIY safe
Once pressure is correct and radiators are bled, press and hold the reset button on the boiler (refer to your Remeha manual for the exact button location on your model) until the boiler attempts to restart. Only reset it a maximum of two or three times — repeated lockouts without a successful restart indicate the fault needs hands-on investigation.
- Check that your boiler's electrical supply is switched on and earthed DIY safe
Confirm the dedicated boiler switch or fused spur is in the on position and has not tripped at the consumer unit. Do not open any electrical panels or attempt to inspect wiring yourself. If you have any reason to believe the earth connection may be at fault — for example, the E3 code persists with good pressure and sensors appear fine — contact an NICEIC-registered electrician to inspect the supply earthing and bonding.
- Call a Gas Safe registered engineer to inspect sensors and wiring Gas Safe engineer
If the E3 code returns after the checks above, a Gas Safe engineer will test each temperature sensor (flow, return, and boiler sensor) for continuity and correct resistance, inspect the wiring looms for damage or corrosion, and reseat any connectors that may have worked loose from the PCB. This requires access to internal components and is not a homeowner task.
- PCB replacement if all other causes are ruled out Gas Safe engineer
If sensor testing and earthing checks come back clear, the control unit (PCB) itself is likely the cause of the E3. A Gas Safe engineer — often working alongside technical support from Remeha — will confirm this diagnosis before ordering and fitting a replacement board. Fitting the wrong PCB or incorrectly commissioning a new one can create further faults, so this must only be done by a qualified professional.
Parts you may need
- Flow or return temperature sensor (NTC) · from £25
- Boiler thermistor / high-limit sensor · from £30
- Remeha Avanta PCB / control unit · from £280
- Sensor wiring harness · from £45
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 £120–£400, depending on the underlying cause.
Frequently asked questions
Is the Remeha E3 code dangerous?
It can be. An earth fault on any electrical appliance is a genuine safety concern, and you should not keep resetting the boiler and ignoring the code. If basic checks (system pressure, bleeding radiators) do not clear it, have the boiler inspected by a Gas Safe engineer and, if an earth fault is suspected, contact an NICEIC-registered electrician to check the supply wiring.
Can I fix the E3 fault myself?
A homeowner can safely check system pressure, bleed radiators, and attempt one or two resets. Beyond that, the fault almost always requires a professional. Sensor testing, wiring checks, and PCB replacement all involve internal components that should only be handled by a Gas Safe registered engineer. Earthing issues require a registered electrician, not a heating engineer.
How much does it cost to fix a Remeha E3 fault?
For most people, the repair falls between £120 and £400. A sensor replacement is typically at the lower end of that range, while a wiring repair or call-out plus labour sits in the middle. If the PCB turns out to be faulty, the total cost including parts and labour can rise to £450–£700, which is why engineers will always rule out cheaper causes first. Engineers in London and the South East tend to charge towards the top of these ranges.
My E3 code came back straight after a reset — what does that mean?
An immediate or very quick return of the E3 code after a reset suggests the fault is genuine and active, rather than a one-off glitch. This pattern most commonly points to a failed temperature sensor or a PCB problem rather than a pressure or air issue. At this point, further resets are unlikely to help and you should book a Gas Safe engineer to carry out a proper diagnostic.