Thermor water heater error codes: meanings and safe checks

Warnings on a Thermor water heater must be interpreted using the exact appliance model: NO on Iono Select, 11 on Top Sealed and W.7 on Aeromax VM R290 belong to different systems. A code points towards a problem, but does not identify a part that automatically needs replacing. If you smell gas or burning, see smoke, or notice water reaching electrical areas, do not attempt a reset and seek professional help.

If you have a problem with your water heater, you can use our free error code finder. It can help you identify errors and understand how to resolve them easily and effectively.

The model determines what the warning means

Thermor sells appliances that produce hot water using different technologies. An instantaneous gas water heater does not work like an electric storage heater or a heat pump cylinder. Boilers can also supply central heating. Although they all ultimately heat the water for your shower, their code tables are not interchangeable, and using an interpretation from another range can lead to the wrong checks.

The information you need is on the rating plate or in the paperwork supplied with the appliance. Record the full model name, product reference and code exactly as displayed, keeping letters, dots and leading zeros. A photograph of the display helps distinguish NO, 01 and W.10, which must not be reduced to a similar-looking number. Do not remove the casing to find a label that is not accessible.

The entries below distinguish Iono Select and Top Sealed water heaters, the Aeromax VM R290 heat pump cylinder, and Logic Micro and Áurea heating equipment. They are not a universal table for every Thermor product. In particular, the Aeromax VM R290 entries must not be applied to Aeromax Split, Aeromax Concept, Alféa or other versions without checking their specific documentation.

Iono Select and Top Sealed: gas water heater warnings

For Iono Select, the available information associates NO with the battery or electronic components. This does not mean replacing the batteries will solve every lockout. Battery replacement is only a reasonable household check when the model has an accessible user battery compartment and its manual allows the task, using the specified battery type and polarity.

Top Sealed uses a different set of alarms covering ignition, flame detection, sensors and combustion control. The table identifies the system involved, but internal causes are diagnostic possibilities rather than confirmed faults. Anything involving gas, combustion or internal wiring requires an appropriately qualified technician.

Code 28 deserves attention because it can appear after another fault. Repeated resets add a second lockout and make the sequence harder to reconstruct. Keeping a photograph of the first warning and noting whether it appeared when a tap was opened or during operation is more useful. The last code displayed is not always the one that best explains how the problem began.

Logic Micro: conflicting entries rule out a generic table

The available Logic Micro compilations contain significant differences. One assigns F1 to low pressure and F2 to flame loss; another, specifically associated with Logic Micro 24, assigns F1 to false flame and F2 to low pressure. Other entries also differ. Without identifying the version and checking its manual, choosing one is not safe simply because it appears more plausible.

This discrepancy matters even when the symptom seems obvious. A boiler with no hot water may be locked out because of pressure, ignition or flame detection. Opening a filling valve because an unrelated table interprets F2 as insufficient water would be unjustified. The comparison below shows where the information conflicts, rather than providing instructions for intervention.

For Logic Micro 24, the available information gives a cold pressure reference of 1 to 1.5 bar. That figure helps put this boiler’s pressure gauge reading into context; it is not a setting for a gas water heater or Aeromax cylinder. Reading the pressure is safe; filling, draining or working on a pressurized circuit is outside the household checks described here.

Aeromax VM R290: the warning may affect only the heat pump

Aeromax VM R290 produces hot water using a heat pump and has an electric backup heater. Its warnings may be preceded by Err and combine letters with numbers. Some stop all heating; others stop the heat pump while electric backup continues. As a result, having hot water does not prove that the appliance has returned to normal operation.

This distinction is especially useful with P codes. A unit that continues heating through its electric element may have lost the heat pump contribution. Leaving it in that condition can increase consumption compared with normal operation, although there is no fixed increase that applies to every home. Backup heating is an intended function, not a repair of the fault.

The sensor thresholds describe readings that the controller considers abnormal; they do not necessarily indicate the actual water or air temperature. Nor does P.40 mean that a component needs replacing. It identifies operation outside the permitted range and requires the circumstances to be assessed before concluding there is a fault. There is no universal range that should be applied to every Aeromax.

W.7 does not automatically mean an empty cylinder either: the ACI system, associated with corrosion protection, provides another possible explanation. Do not force heating to test it or handle connections. With W.10, water may also reach 62 °C while the display remains unchanged; do not trust that reading to judge the temperature available at the tap.

Áurea: heating system codes are not water heater codes

Áurea, Áurea Duo and Áurea Compact R32 are heat pump heating systems, with configurations that can also provide domestic hot water. Their G codes refer to the water circuit, sensors, communications or outdoor unit. Even when the symptom is a cold shower, G11 is not W.7 and does not describe the same circuit.

The G6 family includes a suffix identifying the specific outdoor unit fault. Recording only G6 removes part of the diagnostic information: G6.17 relates to the fan, whereas G6.20 indicates an abnormal low-pressure condition. That distinction affects the professional’s assessment and makes it important to keep the complete code, including the numbers after the dot.

On Áurea versions that support it, emergency mode allows electric backup heating for certain outdoor unit faults. Activation must follow the user manual and suit the installed configuration. It must not be treated as a general option for every alarm: backup has its own conditions and does not justify ignoring overheating or water leaks.

Checks that do not require opening the appliance

Before attributing the entire problem to the heater, observe whether the lack of hot water affects every tap or just one. Low flow at a single outlet may relate to that tap or its accessible aerator. The comparison provides context, but does not override an alarm displayed by the appliance or justify continued operation with a safety warning.

On a heat pump cylinder, visually check that no objects are blocking accessible air grilles. Do not insert tools, touch the fan or dismantle ducts. You can also look for external leaks without touching connections, check user settings and record whether the fault began after a power cut. Observation is not intervention in the water circuit or electrical installation.

H.15 on Aeromax VM R290 is an example of an accessible setting: correcting the date and time restores meaningful scheduling. An inconsistent temperature reading, however, is not resolved by entering installer menus. Sensor measurements, circuit board tests and calibration require professional diagnosis. Do not buy a sensor merely because a code mentions temperature: its connection or the circuit interpreting its signal could also be at fault.

A reset does not prove the fault has gone

A reset allows the controller to try operating again when the specified conditions are met. It does not correct poor combustion, a leak, a faulty sensor or inadequate circulation. Use only the control and procedure specified for the model, without inventing a button-hold duration. If the warning returns, stopping further attempts is safer than repeating them.

Before a permitted reset, record the code and when it appears. A lockout immediately after hot water is requested, after several minutes or when changing modes provides different clues. There is no need to provoke the fault repeatedly to document it. Routinely cutting the power is also unwise, particularly when there is an intermittent power supply warning such as W.19.

If you smell gas, do not operate switches or plugs and avoid flames; leave the area and contact the gas emergency service from a safe location. If there is smoke, a burning smell, overheating or water near electrical parts, stop using the appliance. The absence of a code does not make those symptoms safe.

Diagnosis should come before replacement parts

A circuit board warning does not justify replacing the board without further assessment, just as a flame alarm does not automatically identify a faulty valve. The code is the starting point for diagnosis. Before committing to an expense, the assessment should distinguish a confirmed fault from checks still required, and the quotation should define its scope: callout, diagnosis, labour and materials, according to the professional’s terms.

The available information contains no reliable repair tariff that would allow a price to be assigned to each code. The decision to repair or replace depends on age, cylinder or heat exchanger condition, previous faults and parts availability. A minor repair and a structural problem are not assessed in the same way. The code alone cannot establish how long a replacement part will take to become available either.

If the appliance is still covered by a warranty, check its terms before authorizing work or dismantling it yourself. Coverage should not automatically be assumed lost, but outside intervention can complicate the assessment of what caused the damage. Keeping the appliance closed, retaining its identification and recording the warning preserves useful information for your decision without adding a second fault to the first.