Main
No Central Heating Circulation
Radiators do not heat up even though the 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 pump, Stuck diverter valve (on combi), Closed motorised valves, Airlock in system
How to Fix / Troubleshooting
Safety: Ensure the system is not overheated before touching components. Isolate power before removing covers.
- Check room thermostat and programmer: Confirm that heating is actually being called for (thermostat turned up, programmer ON).
- Feel flow and return pipes: Carefully touch the flow and return pipes under the Main boiler. If flow is hot but radiators are cold, circulation is restricted.
- Bleed radiators: Remove air from all radiators, starting upstairs.
- Engineer tasks:
- Check the Main pump for operation and replace if seized or not circulating.
- Inspect and free or replace the diverter valve on Main combi boilers.
- Test external motorised valves (2-port/3-port) for correct operation.
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Repair Difficulty
Medium
3/5
Required Part
Diverter Valve
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