Boiler starts but shuts down after a few seconds, radiators remain cold, no error code displayed.

Safety first: Short cycling wastes energy and stresses components but is not usually an immediate safety risk. However, repeated overheating can cause damage.

Step-by-step checks:

• 1. Open radiators: Ensure at least a few radiators are fully open to provide adequate flow.
• 2. Check bypass: If a bypass valve is installed, ensure it is set according to system design so that some flow is always available when TRVs close.
• 3. Adjust pump speed: Increase pump speed if set too low, following Viadrus guidelines.
• 4. Check filters and strainers: Clean any system filters to reduce flow resistance.

When to stop: If short cycling persists, a heating engineer should review system design and boiler sizing.