🏠 Why Connecting a Gas Boiler to a VMC Needs Extra Care
When installing a wall-mounted gas boiler in a home equipped with a Gas VMC system (Controlled Mechanical Ventilation), safety is not optional — it's mandatory.
To avoid any risk from exhaust fumes not being properly extracted, the boiler must be linked to the ventilation system. If the ventilation fails, the boiler must automatically shut down. And this is made possible using a DSC relay and an air pressure switch.
⚙️ The Role of the DSC Relay and Pressure Switch
✅ What Does the DSC Relay Do?
The DSC reversing relay ensures that the boiler only operates if the VMC system is actively extracting stale air. It acts like a safety switch.
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If the air is properly extracted → the relay allows the boiler to run.
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If the VMC stops working → the relay cuts the power, stopping the boiler immediately.
✅ How the Air Pressure Switch Works
The air pressure switch continuously checks the vacuum level in the VMC unit.
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If suction is present, the switch closes the circuit, energizing the relay.
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If there is no depression or airflow, the switch opens, the relay deactivates, and the boiler is powered off.
🚨 What Happens in Case of Failure?
As soon as the VMC system stops or the vacuum drops:
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The relay coil is no longer powered.
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The contact between L1 and terminal 6 opens → cutting power to the boiler.
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A warning light activates, signaling an extraction issue.
This protects the building and its occupants from any risk due to poor ventilation or gas accumulation.
🔧 Installation Note
Each apartment or home unit should have its own DSC relay setup. A test contact is included in the design to allow maintenance staff or technicians to simulate failures and check if the safety system reacts properly.
🧠 Conclusion
Connecting a wall-mounted boiler with a gas VMC system is not just technical — it’s about safety. By integrating a DSC relay and air pressure switch, you ensure that the boiler only works when air extraction is confirmed. This simple yet smart setup protects lives, prevents gas buildup, and ensures your installation meets all regulations.
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