Safety first: Turn off power before opening pump wiring boxes or zone valve heads. System water may be hot.

Step 1 – Check boiler temperature: Verify that the Rheem boiler is reaching its setpoint temperature on the display. If it is hot but emitters are cold, the issue is with circulation.
Step 2 – Verify pump operation: Listen and feel the circulation pump. If it is silent or only humming without moving water, it may be seized. A technician should test and replace the pump if needed.
Step 3 – Bleed air: Bleed radiators and high points to remove trapped air. Airlocks can completely stop flow.
Step 4 – Check valves: Ensure all isolation valves, balancing valves, and zone valves are open and operating. Manually open zone valves to test flow.
Step 5 – Clean strainers: If installed, clean any Y-strainers or dirt separators in the system. Blockages here can prevent circulation.

Warning: Do not run the boiler for extended periods without confirmed circulation; this can cause overheating and damage.

Boiler runs but radiators or underfloor heating remain cold

Possible Causes