Remeha E.00.05 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.00.05 fault code mean?
The E.00.05 code indicates that your Remeha boiler has detected a short circuit in the return temperature sensor — the NTC thermistor that monitors how hot the central heating water is when it arrives back at the boiler. Because the sensor is sending a shorted, unreliable signal, the boiler's control board can no longer make safe decisions about heat output, so the boiler locks out as a precaution. This code sits within the broader E.00.xx family: E.00.04 typically signals an open circuit (broken connection) on the same sensor, while E.00.05 points specifically to a short circuit. Both codes ultimately mean the return sensor circuit needs investigation, but E.00.05 implies the resistance across the sensor or its wiring has collapsed rather than gone open.
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
- Short circuit in the sensor wiring Common
The wiring between the return NTC thermistor and the control board has developed an internal short — two conductors touching where they shouldn't. This is the most specific fault E.00.05 is designed to flag, and is often caused by chafed insulation, a pinched cable, or moisture ingress at a connector.
- Failed return NTC thermistor Common
The thermistor itself has broken down internally, causing its resistance to drop to near zero and appear as a short to the control board. NTC sensors degrade over time, particularly in systems with poor water quality or where the sensor has been exposed to excessive heat.
- Loose, corroded, or damaged connector plug Sometimes
The plug that connects the sensor wiring to the boiler's harness can work loose, corrode, or suffer pin damage. A partially detached or corroded plug can create a low-resistance path that the board interprets as a short circuit.
- Sensor physically dislodged from the return pipework Sometimes
The return sensor is typically a small clip-on probe seated against the return pipe, sometimes hidden beneath insulation. If it has slipped off or been knocked loose, its readings become erratic and can trigger sensor fault codes.
- Faulty PCB or control unit Rare
If the sensor, its wiring, and all connectors test correctly with a multimeter, the fault may originate inside the control board itself — a damaged input channel or failed component on the PCB can misread a healthy sensor as shorted.
How to fix it
- Check your boiler's system pressure DIY safe
Look at the pressure gauge on the boiler front panel. It should sit between 1.0 and 1.5 bar when cold. If it has dropped below 1 bar, top it up via the filling loop following your boiler's manual. Low pressure alone rarely causes E.00.05, but it is a good baseline check before anything else.
- Attempt a single boiler reset DIY safe
Press and hold the reset button (or follow the reset procedure in your Remeha manual) once. If the boiler fires up and runs normally, monitor it over the next 24 hours. Do not reset more than two or three times in total — repeated resets on a sensor fault can mask a worsening problem and should be avoided.
- Visually inspect the sensor and its wiring (do not disconnect or probe live components) DIY safe
With the boiler powered off, you can open the casing if you are confident doing so, and check whether the return sensor clip is still seated on the return pipe and that the cable runs to it without obvious kinks, burn marks, or chafing. Do not attempt to disconnect wiring or test live circuits — note what you see and report it to your engineer.
- Have a Gas Safe engineer test the sensor resistance and wiring continuity Gas Safe engineer
An engineer will use a multimeter to measure the thermistor's resistance at a known temperature and compare it against the manufacturer's specification. They will also check the wiring loom for continuity and insulation breakdown to confirm whether the short is in the sensor itself or the cable.
- Replace the return NTC thermistor if confirmed faulty Gas Safe engineer
If testing shows the sensor has failed, the engineer will fit a new return NTC thermistor, ensure it is correctly clipped to the return pipe, and clear the fault code. The boiler should then be run through a full heating cycle to confirm normal operation.
- Have the wiring loom inspected and repaired if the sensor tests good Gas Safe engineer
If the thermistor resistance is within spec but the fault persists, the engineer will trace the wiring harness for damaged insulation or a shorted section and carry out a repair or partial loom replacement as needed.
- Have the PCB assessed if all wiring and sensor checks pass Gas Safe engineer
A control board with a faulty sensor-input channel can generate E.00.05 even when everything downstream is fine. PCB diagnosis and replacement must be carried out by a Gas Safe registered engineer, and replacement boards should be sourced from a reputable Remeha parts supplier.
- Call a Gas Safe registered engineer if the fault returns after reset or you cannot resolve it yourself Gas Safe engineer
If the boiler locks out again after a reset, or if you are in any doubt, book a Gas Safe registered engineer experienced with Remeha appliances. Do not continue attempting resets or operating the boiler in a fault state.
Parts you may need
- Return NTC thermistor (temperature sensor) · from £22
- Sensor connector plug and terminal kit · from £12
- Wiring harness section (return sensor loom) · from £45
- Remeha PCB / control unit · from £280
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 £110–£300, depending on the underlying cause.
Frequently asked questions
Is E.00.05 different from E.00.04 on a Remeha boiler?
Yes, though both codes point to the return temperature sensor circuit. E.00.04 indicates an open circuit — the signal from the sensor has been lost entirely, suggesting a broken wire or disconnected plug. E.00.05 indicates a short circuit — the resistance in the sensor circuit has collapsed, often meaning the thermistor itself has failed internally or two wires are touching. An engineer will test both possibilities as part of the same diagnosis.
Can I fix Remeha E.00.05 myself?
Your safe DIY options are limited to checking system pressure, topping up via the filling loop if needed, and attempting a single reset. Any work involving the sensor, wiring, connectors, or PCB must be carried out by a Gas Safe registered engineer. Working on live internal wiring or gas-related components without the correct registration is unsafe and illegal in the UK.
How much will it cost to fix E.00.05 in the UK?
For most people, the repair involves replacing the return NTC sensor and comes in at roughly £110–£300 all-in, covering the call-out, labour, and the part itself. If the problem turns out to be a damaged wiring loom the bill can sit towards the top of that range. A PCB replacement is a less common outcome but significantly more expensive — typically £350–£500 or more once parts and labour are included — so it is worth asking your engineer to rule out the sensor and wiring first.
Why does my Remeha keep showing E.00.05 after I reset it?
A fault that returns immediately or within a short time after reset almost always means the underlying hardware problem — a failed sensor, a shorted cable, or a corroded connector — has not been resolved. Repeated resets will not clear a genuine component fault and may delay a proper repair. Book a Gas Safe engineer to carry out a proper electrical test of the sensor circuit rather than continuing to reset.