Vaillant Poor Heating Performance / No Circulation

Radiators or underfloor heating not getting hot even though Vaillant boiler appears to run

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Seized or failed circulation pump, Air lock in system, Closed motorized zone valve, Sludge-blocked filter or pipework

How to Fix / Troubleshooting

Safety: Allow system to cool before bleeding radiators.

User checks:

  • Verify that the room thermostat and programmer are calling for heat.
  • Check system pressure and top up if low.
  • Bleed radiators to remove trapped air.
  • Feel the flow and return pipes at the boiler; if hot but radiators are cold, a zone valve may be closed.

Professional checks:

  • Test the circulation pump for operation and replace if not circulating.
  • Check and free or replace motorized zone valves.
  • Clean system filters and consider a powerflush if sludge is present.
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Repair Difficulty

Medium 3/5

Required Part

Circulation Pump
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