Heatrae Sadia indirect unvented cylinder does not heat from the boiler, but immersion works.

Safety first: Boiler and cylinder primary circuits can be hot and pressurised. Allow to cool and depressurise where necessary.

Steps to restore indirect heating:

• 1. Check boiler and controls: Ensure the boiler is operating and that the cylinder call-for-heat (via programmer and thermostat) is active.
• 2. Verify motorised valve: Check that the motorised valve feeding the cylinder coil opens when there is a demand. Replace if stuck or failed.
• 3. Check primary pump: Confirm the circulation pump runs when the cylinder is calling for heat. Replace or free if seized.
• 4. Bleed air: Bleed any air vents on the primary circuit and at high points to remove airlocks.
• 5. Coil blockage: If flow and pump are good but coil remains cold, the coil may be blocked with sludge or scale and may require powerflushing or cylinder replacement.