A boiler that ignites but never distributes heat because the circulator pump isn't turning is one of the more common hydronic system failures.
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Quick answer
A gas boiler circulator pump that will not run is usually stopped by one of a small number of causes: no power reaching the pump from a tripped relay, blown fuse, or wiring fault; a seized impeller or shaft, often from mineral buildup or a pump that sat unused for a long period; a failed pump motor or capacitor; or a control board that is not sending the signal to run it because a thermostat call, zone valve, or aquastat is not completing the circuit. A licensed technician isolates which of these it is with a meter and a visual inspection rather than guessing.
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The circulator pump is what actually moves heated water from the boiler out to the radiators or baseboards and back again. A boiler can fire, heat its internal water, and reach temperature perfectly normally while the circulator pump sits completely idle, which means the house stays cold even though the boiler itself shows no fault and may even cycle on and off normally as it reaches its own internal setpoint. This is one of the more common reasons a homeowner reports the boiler seems to be running fine but the house is not warming up.
Electrical causes are common: a tripped relay or contactor, a blown fuse dedicated to the pump circuit, a failed pump capacitor on single-phase motors that need it to start, or a wiring connection that has loosened or corroded over time. Mechanical seizure is another frequent cause, particularly in pumps that have been sitting idle for an extended period, such as over a summer with no heating demand, when mineral deposits or light corrosion inside the pump housing can lock the impeller in place; some pumps free up with a manual nudge to the shaft, though this should be done by a technician who knows the correct method for the specific model.
Control-side causes can look identical to a dead pump from the homeowner's perspective: if the thermostat is not calling for heat, a zone valve is not signalling it has opened, or an aquastat controlling pump operation based on boiler water temperature is miswired or has failed, the pump may be entirely healthy but simply never receiving the signal to run.
Listen closely at the pump when the thermostat is calling for heat: complete silence with no hum at all suggests no power is reaching it, while a humming sound with no visible shaft movement, if the pump has a visible shaft cap, can suggest a seized impeller. Check the thermostat is actually calling for heat and showing a setpoint above room temperature. If there is a visible reset or bleed screw on the pump, do not attempt to force it unless you are confident, since pumps handle hot pressurized water and can release water or heat unexpectedly when opened.
A pump that is seized but otherwise mechanically sound can sometimes be freed and returned to service, though this is often a temporary fix if internal wear has already begun, and many technicians recommend replacement rather than repeatedly freeing an aging pump. A pump replacement itself is a routine, well-understood job on almost any residential boiler and does not typically require touching the boiler's burner or heat exchanger at all, so it should not be confused with a bigger boiler repair or replacement decision.
Safety note
Circulator pump work involves both electrical components and hot, pressurized system water; the system should be depressurized and cooled before any pump service. If you smell gas near the boiler while investigating this issue, leave the home and call FortisBC at 1-800-663-9911.
This is a classic sign the circulator pump is not moving water even though the boiler itself is firing and reaching temperature normally, since the two functions are largely independent.
Yes, this is a fairly common occurrence, especially in older pumps, and is one reason some technicians recommend a quick run-test at the start of each heating season rather than waiting for the first cold night to find out.
This should be left to a licensed technician, since it usually requires the system to be properly isolated and the correct method varies by pump model.
A technician checks whether the pump is actually receiving a call for power at all; if it is receiving power and still not running, the pump itself is the issue rather than the thermostat or wiring upstream of it.
It is generally one of the more affordable and contained hydronic repairs, with the exact cost depending on the specific pump and system, best quoted after inspection.
The boiler itself typically has its own protections and will not be damaged by a dead pump, though prolonged operation without circulation can occasionally trip a high-limit safety control or lead to localized overheating in some designs, so it is still worth addressing promptly.
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