Vaillant Short Cycling / Oversized Boiler or Control Issue

Boiler frequently short cycles (turns on and off rapidly) without reaching set temperature

Possible Causes

Boiler output too high for system, Incorrect control settings, Faulty temperature sensor causing premature shutdown, Poor system water volume or bypass setting

How to Fix / Troubleshooting

Safety: No immediate hazard, but efficiency and component life are reduced.

User actions:

Ensure all radiators are open to increase system load.
Check that the room thermostat is not located too close to the boiler or a heat source.

Professional actions:

Adjust boiler maximum output via installer settings to better match the system.
Check NTC sensors for correct operation.
Verify bypass valve setting and system design.

Repair Difficulty

Easy 2/5

Required Part

Room Thermostat / Control Settings

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