Radiators are cold but boiler appears to run and hot water works

Safety: Electrical isolation is required before working on internal components.

• Check controls: Ensure the room thermostat is calling for heat and that any programmer is set to heating ON.
• Valve positions: Confirm that the heating flow and return isolation valves under the Junkers boiler are fully open.
• Listen for pump: When heating is demanded, place a hand on the pump body to feel for vibration and warmth.
• Technician tasks:
  • Test and, if necessary, replace the circulation pump.
  • Inspect and free or replace the three-way diverter valve motor and cartridge.
  • Check wiring from thermostat to boiler and repair any breaks.