upstairs radiator not working

Possible reasons:

Loss of heating water

• Failing safety valves
• Failing automatic air release valves
• Tenants or house cleaners misusing (radiator breathing) valves as water supply

Leaks in the heat exchanger or pipe system, valves or radiators

Expansion tank

• Incorrect pressure setting in air chamber
• Failing membran
• Leaks

Air in the system

Heating water circulation pump:

• Stucked shaft
• Failing phase capacitor
• Turbine eroded by sand/rust/hard parts, cavity problems

Blocked (bypass/thermostat) valves, the tiny rods/shafts of thermo valves are prone for getting stucked

Input/output pipes of radiators/radiator valves mixed up

Blocked pipes (metal/rust parts/dirt)