Beretta - Arçelik - Riello Combi Boiler Water Pressure Sensor (Transducer) 505.91590 / R10028142 – 0…4 bar, 24 V, Push-Fit Type

Analog water pressure sensor (transducer) from the Huba Control Type 505 family. It continuously measures the water pressure in the combi boiler's heating circuit and reports it to the PCB as a voltage signal. It differs from an on-off pressure switch: it reads the pressure numerically at every moment, not only at the threshold value.

This product is the 505.91590 variant: 0…4 bar measuring range, 0.5…3.5 V output, 24 V (8.5…30 V) supply, threadless push-fit (O-ring) port. Beretta spare part code R10028142, Riello 4365904, Vokera 10028142.

🚨 Before Ordering: Read the IN Line on the Body

Huba manufactures the same 0…4 bar sensor in two different supply voltages, and the two cannot be distinguished from the outside — the body, push-fit port, O-ring and connector are exactly the same:

🚨 The output label is the same on both variants (OUT: 0.5…3.5 V) — it is not distinguishing. The only identifying mark is the IN: line on the body. If your removed part says IN: 24 (8.5…30) V, you have the right product.

If the wrong variant is fitted: if the 5 V sensor is fitted to a 24 V circuit it will be damaged; if the 24 V sensor is in a 5 V circuit, it gives no reading at all because it needs at least 8.5 V supply, and the PCB constantly generates a low pressure error.

What This Product Is Not

• It is not a 0.45 bar pressure switch. Beretta and Vokera appliances also have a separate on-off water pressure switch (Beretta R2044 / R10028141, Vokera 20003181). This product is an analog transducer.
• It is not the Ferroli Divatop sensor — that appliance uses Huba 505.91512 (Ferroli code 39818770).
• It is not the Buderus / Sieger sensor — they use Huba 505.99023 (Buderus code 7101436).

Compatible Models

🪤 Note on the Arçelik side: Arçelik condensing combi boilers share the Riello–Beretta platform and this part is also used in Arçelik appliances in the field; however, Arçelik has no published spare part code of its own for this sensor. For your Arçelik appliance, compare the code and the IN value on the body of the removed sensor.

Fault Symptoms

The typical picture is this: the pressure gauge shows 1.2–1.5 bar, there is water in the system, no leak — but the combi boiler persistently gives a low water pressure error and does not run. Topping up with water and resetting do not help.

Definitive Diagnosis by Measurement

This sensor is not tested by ohm (resistance) measurement — it is not an NTC, it has integrated electronics inside. The correct method is to measure voltage. The transfer function is linear:

Output voltage = 0.50 V + (0.75 × pressure)

1. Supply check: There must be 8.5…30 V (typically 24 V) between IN and GND. If not, the fault is not in the sensor but in the PCB or the cable.
2. Output check: Measure the OUT – GND voltage and compare it with the pressure on the gauge using the table.
3. Interpretation: If the values match, the sensor is sound — investigate a leak, the expansion vessel, the safety relief valve or air in the system. If you read OUT ≈ 0.5 V while the gauge shows 1.5 bar, the sensor or the cable is faulty.
4. Mechanical check: if the port is blocked with sediment, the sensor reads low even though it is sound; when removed, clean the O-ring seat and the mouth of the hole.

🪤 The output starting from 0.5 V instead of 0 V is intentional (live zero). In this way a broken cable (0 V) can be distinguished from a true zero pressure.

Connection and Pin Layout

The connector is RAST 2.5 (AMP DUOPLUG 2.5), 3-pin. Viewed from above with the vertical text on the body on the right:

The manufacturer recommends that the sensor be mounted with the electrical connection facing upwards.

Technical Specifications

🪤 The retaining clip that holds the sensor in its seat is a separate part (Huba 112442) and is not included with this product. If your old clip is sound, it is reused.