Boiler intermittently shuts down with error 19, often during modulation or when demand changes.

Safety first: Isolate power at the breaker before opening the boiler casing. Do not work on live circuits.

• Check power supply: Verify that the boiler is connected to a dedicated circuit with correct voltage and polarity. Avoid using extension cords or shared outlets.
• Inspect earth/ground: Confirm that the earth wire is securely connected at the boiler terminal block and that the building's grounding system is intact.
• Tighten wiring connections: With power off, gently tug each connector on the main control board and terminal block to ensure it is fully seated. Look for signs of heat damage or discoloration.
• Monitor for external interference: Large motors or welders on the same circuit can cause interference. If possible, separate the boiler circuit from heavy loads.
• Professional diagnosis: If error 19 persists, a technician should test the control PCB and replace it if necessary.