A70
Buderus Room Thermostat / Room Sensor Communication Fault

Boiler shows A70; heating curve or room temperature control not functioning correctly

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Disconnected or faulty Buderus room sensor, Broken BUS cable (e.g., EMS/EMS+), Incorrect control configuration, Faulty room controller (e.g., RC35, RC300)

How to Fix / Troubleshooting

Safety: Isolate power before working on low-voltage control wiring.

  • 1. Check controller display: If using a Buderus room controller (e.g., Logamatic RC series), verify it powers on and shows no local errors.
  • 2. Inspect BUS wiring: Check the two-wire EMS/EMS+ BUS cable between the boiler and room controller. Ensure polarity is correct and terminals are tight.
  • 3. Cable continuity: Use a multimeter to check continuity of the BUS cable. Repair or replace if open or shorted.
  • 4. Control configuration: In the boiler or Logamatic menu, verify that the correct type of room control is selected. If no room sensor is used, disable that option.
  • 5. Replace controller: If wiring is sound but A70 persists, the room controller or boiler control board may be defective and require replacement.
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Repair Difficulty

Medium 3/5

Required Part

Buderus Room Controller / Room Sensor
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