Remeha E.00.20 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.00.20 fault code mean?
The E.00.20 fault code indicates that the boiler's flue gas temperature sensor (an NTC thermistor mounted on the flue outlet pipework) is either disconnected from the circuit or is returning a reading that falls below the expected measurement range. Because the control board cannot verify a valid flue temperature, the boiler treats this as a safety issue and enters a hard lockout — it will not restart until the underlying fault has been resolved and the boiler is manually reset. In practice this usually points to a wiring or connection problem rather than a failed sensor outright, though sensor failure is also possible.
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
- Open circuit or broken wiring to the flue sensor Common
The most frequent cause. A break in the sensor cable — caused by physical damage, chafing, or a connector that has worked loose over time — means no signal reaches the control board. The board interprets the absence of a reading as a below-range fault and locks out the boiler.
- Loose or corroded connector Common
Even if the cable itself is intact, a poor connection at either end — at the sensor plug or at the PCB header — can interrupt the signal. Corrosion on the pins, or a connector that has never been fully clicked home, is a common finding when engineers inspect this fault.
- Incorrectly seated or dislodged sensor Sometimes
The flue NTC sensor must be firmly clipped into its designated mounting point on the flue outlet. Vibration, poor original installation, or accidental disturbance during servicing can cause it to sit incorrectly, preventing it from making reliable contact and producing an out-of-range reading.
- Failed flue gas temperature sensor Sometimes
NTC thermistors do fail over time — internal resistance can drift outside specification or the sensor can develop an open circuit internally. When all wiring and connections check out correctly, a faulty sensor is the likely remaining explanation.
- PCB fault affecting the sensor input circuit Rare
In rare cases, damage to the control board's sensor input circuitry can make a healthy sensor appear to be open-circuit. This is typically only considered after the sensor and all wiring have been verified as good.
How to fix it
- Do not attempt to restart the boiler repeatedly DIY safe
A hard lockout on a Remeha boiler requires the fault to be fixed before a reset will hold. Pressing reset more than two or three times without addressing the cause will not help and may mask useful diagnostic information for an engineer.
- Check that the boiler has not been recently serviced or worked on DIY safe
If an engineer or installer has recently worked on the flue or the boiler internals, a disturbed sensor connection is the most likely explanation. Note this information to pass on to the attending engineer, as it will help them locate the fault quickly.
- Visually inspect the flue sensor cable where it exits the boiler casing (do not touch internal components) DIY safe
From outside the boiler casing, you may be able to see whether the sensor cable is obviously damaged, kinked sharply, or has a plug that has pulled free at the boiler end. Do not open the casing or interfere with any wiring — simply note what you can observe and report it to the engineer.
- Arrange for a Gas Safe registered engineer to inspect the sensor wiring and connectors Gas Safe engineer
The engineer should check the full cable run from the flue sensor to the PCB, looking for breaks, chafing, or loose connectors. A multimeter resistance check will confirm whether the cable and sensor are electrically intact.
- Engineer to verify correct sensor seating and re-seat if necessary Gas Safe engineer
The flue NTC sensor must be clipped securely into its mounting bracket on the flue outlet. The engineer should confirm it is correctly positioned and fully engaged, as a partially seated sensor can produce an intermittent or out-of-range signal.
- Engineer to test sensor resistance with a multimeter Gas Safe engineer
A known-good Remeha flue NTC sensor will produce a predictable resistance value at ambient temperature. If the measured resistance is open-circuit or wildly out of specification, the sensor itself has failed and requires replacement with a genuine Remeha NTC sensor.
- Engineer to replace the flue gas temperature sensor if found to be faulty Gas Safe engineer
Genuine Remeha NTC flue sensors are available from UK heating spares suppliers and can usually be sourced for next-day delivery. The part is relatively inexpensive; the main cost is engineer time. After fitting, the engineer should verify the new sensor reads a plausible temperature before resetting the boiler.
- Reset the boiler after the fault has been rectified DIY safe
Once the engineer confirms the underlying fault has been resolved, press the RESET button on the boiler's control panel. The boiler should power up normally and the E.00.20 code should clear. If the lockout returns promptly, further investigation of the PCB or wiring loom is needed.
- If fault persists after sensor and wiring checks, call a Gas Safe registered engineer to assess the PCB Gas Safe engineer
In rare cases where the sensor and all wiring test good, the fault lies in the PCB's sensor input circuitry. PCB diagnosis and replacement must only be carried out by a qualified engineer.
Parts you may need
- Remeha flue gas NTC temperature sensor · from £35
- Sensor connector / wiring harness (flue sensor side) · from £20
- Remeha PCB (control board) — if required · from £320
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 £100–£280, depending on the underlying cause.
Frequently asked questions
Can I fix the E.00.20 fault myself?
The only safe DIY actions are to note whether the boiler has been recently worked on, do a visual check of the external cable run, and attempt a single reset after speaking to an engineer. Any inspection of the internal wiring, sensor connections, or PCB must be carried out by a Gas Safe registered engineer. Working on boiler wiring without the correct qualification is unsafe and potentially illegal in the UK.
How much will it cost to fix a Remeha E.00.20 fault?
For most households, the repair involves an engineer call-out, a wiring check, and either a re-seat of the sensor or a sensor replacement. Expect to pay roughly £100–£280 in total for this work. If the sensor only needs re-connecting or re-seating, the bill will be towards the lower end. If a new NTC sensor is needed, the part itself typically costs £20–£50 and the rest is labour. In the uncommon situation where the PCB is also damaged, a board replacement can add several hundred pounds to the cost — but this is unusual for this particular fault code.
Why has my Remeha boiler locked out rather than just showing a warning?
The flue gas temperature sensor is a safety-critical component. If the control board cannot confirm a valid flue temperature reading, it cannot safely verify combustion conditions, so it shuts the boiler down completely rather than risking unsafe operation. This hard lockout behaviour is by design and means the boiler will not attempt to fire again until both the fault is fixed and the reset button is pressed manually.
Could the E.00.20 fault come back after it has been fixed?
If the repair fully addresses the root cause — for example, a new sensor is fitted and connections are secure — the code should not return. Intermittent recurrence usually means the underlying problem was not fully resolved: a connector that looks seated but is not fully clicked home, or a hairline break in the cable that only shows up when the boiler heats up and the wiring flexes slightly. Ask the engineer to check the full cable run rather than just the sensor end if the fault returns.