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Troubleshoot the BRU relay (Gen2)

Gen2 BRU relay troubleshooting

warningThis process involves accessing the internals of electrical equipment that may be at mains voltage. It should only be carried out by an electrically competent person who is comfortable with the process and the risks involved (e.g. an electrician).

It is possible that although the Switchee appears to be working, the BRU isn’t actually sending signals to the heating system. Vice versa, it's also possible that the BRU is sending signals, but these are not being received by the heating system (e.g. damaged PCB). The intention of this guide is to detail the process for a technical support agent to walk an engineer through testing the terminals on a boiler receiver unit.

Checking the Switchee equipment

The below process can be undertaken to confirm the BRU is correctly sending signals as required.

  1. Installer isolates all power to the heating system and opens BRU casing.
  2. Remove the orange terminal block so the wiring for COM, NO-H, NO-W, NC-W are removed
  3. Carefully reapply power to the BRU.
  4. With the Gen2 head unit not calling for heating, measure between the following using a multimeter in resistance mode
    1. Between COM and NO-Heat - should measure open circuit.
    2. Between COM and NO-Water - should measure open circuit.
    3. Between COM and NC-Water - should measure short circuit.
  5. Now, with the Gen2 calling for heating and hot water, measure between the following using a multimeter in resistance mode
    1. Between COM and NO-Heat - should measure short circuit
    2. Between COM and NO-Water - should measure short circuit
    3. Between COM and NC-Water - should measure open circuit

Screenshot 2025-12-16 at 16.54.30

If the above proves true - the Switchee BRU is working as intended.

Checking beyond the Switchee system

The next things for an engineer to check are:

  1. That the wiring is well connected into the Switchee BRU (the orange connectors)
  2. Trace those wires to their other end (at the heating system, zone valve, wiring centre etc) and redo the tests in the top section to confirm that the same results are seen at that end of the wires. If not, then the wiring is at fault.
  3. When doing this, leave the wires connected to the orange terminal block but dis-connect them from whatever they are connected to at the other end, then test across the disconnected ends of the wires. Take care to isolate mains power before disconnecting the wiring

If the wiring is not at fault then the problem lies either with the unit that the wires are connected to (the heat pump, zone valve etc) or with the overall wiring configuration for the heating system (either of these are beyond Switchee’s remit)

For more support, contact our installer support team directly on:
Tel: 0800 133 7957 | Email: install@switchee.com