Boiler water not circulating to radiators

There are a number of factors that can disrupt the normal circulation of boiler water to radiators. This guide is intended to help you understand how the boiler water circulation system works and identify any DIY fixes that may eliminate the need for a service call out. Be aware, however, that repairs to circulating pumps, pump control mechanisms, or pump power supplies should be left to qualified professionals.

Check pump control system

Make sure that the boiler’s timer and/or programmer is turned on and set correctly. Make sure that a room thermostat is set well above current room temperature. Make sure that the system is properly pressurized per the manufacturer’s recommendations.

Adjust the boiler thermostat setting upward from its normal position. Then switch the boiler to the off position. The pump may continue to run for a while before shutting down. After 5-10 minutes, switch the boiler to the on position. Adjust the boiler thermostat downward. You should hear an audible click when the boiler thermostat attempts to activate the pump.

If continued downward adjustment does not produce a start signal from the boiler thermostat to the circulating pump, there may be a fault with the boiler thermostat or the programmer/timer. Double check that the room thermostat is working correctly before calling in a qualified service person to complete the control system diagnosis.

Check pump motor and power supply

If a start signal is sent from the boiler thermostat to the circulating pump, but the pump does not start, there may be a fault with the power supply to the pump motor or within the pump motor itself. Contact a qualified service professional to confirm the finding and undertake a repair.

Check for airlocks or blockages

If all control systems work properly and the pump motor starts running, but the pipe on the discharge side of the pump remains cold there may be an airlock or a buildup of sludge in or near the pump. There is usually a bleed screw on the pump to relieve an airlock close to the pump. If the problem is not resolved by bleeding, it is time to remove the pump to clean or replace it. If removing the pump is indicated, get assistance from a qualified professional.