Boiler does not start at all for heating, but hot water may still work, even when vSMART calls for heat.

Safety warning: Boiler and control wiring involve mains voltage. Only qualified personnel should work inside the boiler or wiring center.

Steps to check:

• Confirm demand: In the app, raise the setpoint significantly and verify that vSMART indicates an active heating demand.
• Check boiler display: See if the boiler shows a heating demand symbol or any error codes. Reset the boiler if it is in lockout.
• Zone valve check: If you have motorized zone valves, listen or feel for them opening when demand is present. A stuck valve will prevent flow and may block boiler firing.
• Interface test (pro): A technician should test continuity and operation of the vSMART interface output to the boiler and replace it if it does not signal correctly.

If hot water works but heating does not, the fault is often in the heating control path (zone valves, wiring, or interface) rather than the boiler burner itself.