Remeha E.01.12 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.01.12 fault code mean?
The E.01.12 code appears on Remeha boilers when the control board detects that the water returning from the heating circuit is registering a higher temperature than the water leaving the boiler — the opposite of what should happen in normal operation. Because this relationship makes no physical sense under correct conditions, the boiler shuts down to protect itself and prevent inaccurate heat regulation. The root cause is almost always a faulty or mispositioned temperature sensor, a circulation problem, or low water volume in the system. This dot-notation fault code is used on the newer Remeha Ace range; if you own an older Avanta or Quinta, a similar underlying fault would appear as a different code format.
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 mispositioned flow or return temperature sensor Common
If either the flow (supply) or return NTC temperature sensor has drifted out of calibration, developed an internal fault, or has simply been displaced from its correct position on the pipework, the boiler receives contradictory temperature readings. This is the most frequent root cause engineers find when attending an E.01.12 callout.
- Poor electrical connection to a temperature sensor Common
Corroded, loose, or damaged wiring connectors on the flow or return sensor can cause intermittent or permanently incorrect resistance readings, leading the boiler to believe the return is hotter than the flow. Vibration and age both degrade connector quality over time.
- Insufficient system pressure or trapped air Sometimes
Low water pressure (below roughly 1 bar) or a significant airlock reduces water circulation through the heat exchanger. With restricted flow, temperature readings from the two sensors can diverge unexpectedly and trigger this fault. Check the pressure gauge on the boiler front panel.
- Circulation pump failure or blockage Sometimes
If the pump is not moving water around the system effectively — whether due to a seized impeller, internal blockage, or electrical failure — the heat exchanger can overheat on the flow side while the return side stays relatively cool, or sensors register anomalous values. A complete pump failure usually produces other symptoms too, such as radiators not warming up.
- Short circuit within a sensor or its wiring loom Rare
A direct short in the NTC sensor element or along the cable causes the control board to read an artificially low resistance, which it interprets as a very high temperature. This can flip the apparent relationship between flow and return readings.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the boiler's front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1 bar, use the filling loop to top up the pressure slowly until it reaches approximately 1.2 bar, then close the filling loop valve. Low pressure alone can disrupt circulation enough to produce sensor anomalies.
- Bleed any air from the system DIY safe
If you notice cold spots at the top of radiators or gurgling noises in the pipework, air may be trapped in the system. Bleed each radiator using a radiator key — start upstairs and work downwards. Some Remeha Ace boilers also have a built-in auto-vent programme; refer to your user guide to run it. After bleeding, recheck the system pressure and top up again if it has dropped.
- Attempt a single boiler reset DIY safe
Once you have checked pressure and bled the system, press the reset button on the boiler control panel to attempt a restart. Do this once only. If the E.01.12 code returns within a short time, do not keep resetting — repeated resets will not fix an underlying fault and can mask important diagnostic information for the engineer.
- Check that your gas supply is functioning DIY safe
Verify that other gas appliances in the property (hob, gas fire) are working normally. If they are not, contact your gas supplier before doing anything else. If the gas supply is fine, the fault is specific to the boiler.
- Inspect sensor wiring connections — engineer required Gas Safe engineer
A Gas Safe engineer will access the flow and return NTC temperature sensors, check that each sensor is correctly seated against the pipework, and inspect the wiring connectors for corrosion, looseness, or visible damage. Resistance readings will be taken with a multimeter and compared against the manufacturer's specification for the current water temperature.
- Test and replace faulty temperature sensors if necessary — engineer required Gas Safe engineer
If a sensor is reading outside the expected resistance range, the engineer will replace it with the correct Remeha-compatible NTC sensor. Both the flow and return sensors may be tested during the same visit to rule out a second underlying fault.
- Assess circulation pump operation — engineer required Gas Safe engineer
The engineer will check whether the pump is running at the correct speed and moving water freely. If the pump is seized or failing, it will need to be replaced. A pump replacement on an Ace-series boiler is a standard repair that most heating engineers carry out during a single visit.
- Call a Gas Safe registered engineer Gas Safe engineer
If the basic homeowner checks above have not resolved the E.01.12 lockout, contact a Gas Safe registered engineer to carry out the electrical and mechanical diagnostics described. You can verify an engineer's Gas Safe registration at gassaferegister.co.uk. Do not continue to reset the boiler repeatedly while waiting.
Parts you may need
- NTC flow temperature sensor (Remeha Ace compatible) · from £25
- NTC return temperature sensor (Remeha Ace compatible) · from £25
- Central heating circulator pump (suitable replacement) · from £75
- Sensor wiring loom / connector harness · from £30
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–£380, depending on the underlying cause.
Frequently asked questions
Can I fix Remeha E.01.12 myself without an engineer?
A few preliminary checks are safe to carry out yourself: topping up system pressure via the filling loop, bleeding radiators to remove trapped air, and attempting a single reset. However, if these steps do not clear the fault, the underlying cause almost certainly involves testing or replacing temperature sensors, checking internal wiring, or diagnosing the circulation pump — all of which require a Gas Safe registered engineer. Do not repeatedly reset the boiler hoping it will resolve itself.
How much does it cost to fix an E.01.12 fault on a Remeha boiler?
Most homeowners pay somewhere between £120 and £380 all-in, depending on what the engineer finds. A sensor replacement with labour typically falls in the £130–£220 range, while a pump replacement usually costs £180–£350 including parts and labour. If the PCB turns out to be at fault — which is uncommon with this code — the bill could exceed £400, but that scenario is relatively rare. Always ask for a written quote before work begins.
Which Remeha models show the E.01.12 code?
The dot-notation fault code system, including E.01.12, is used on the Remeha Ace series: the Tzerra Ace, Avanta Ace, and Calenta Ace. Older Remeha models such as the original Avanta and Quinta use a different fault code format (typically a plain E-code), so the same underlying fault would display differently on those boilers.
Why does E.01.12 say the return is hotter than the flow — is that physically possible?
In normal operation it is not: the flow should always leave the boiler warmer than the water returning from the radiators. When E.01.12 appears it does not necessarily mean the return water literally is hotter; rather, one or both sensors are reporting incorrect temperatures that create this impossible relationship on paper. That is why sensor faults and poor electrical connections are the most common culprit, rather than a genuine reversal of water temperature.