Laars boiler problems generally fall into a handful of categories: ignition faults, circulator pump issues, venting blockages, low system pressure, and heat exchanger scale.
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The most common Laars boiler problems fall into a few recurring categories: ignition or pilot faults that prevent the burner from lighting, a circulator pump that's noisy, leaking, or seized after a period of low demand, low system pressure from a slow leak or a failing expansion tank, venting or chimney issues that trigger a safety shutdown, and heat exchanger scale that reduces efficiency and can cause kettling noise. Diagnosing which category applies usually takes a technician a short visit, since several of these can produce similar symptoms like uneven heat or a no-heat call.
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Older Laars boilers with a standing pilot rely on a thermocouple to prove the pilot flame is lit before allowing the main gas valve to open. A worn or fouled thermocouple is one of the more common reasons a pilot won't stay lit, and it's usually a straightforward, inexpensive fix rather than a sign of a bigger problem.
Newer units with electronic ignition instead rely on a flame sensor and ignition module, and a fault here tends to show up as repeated ignition attempts followed by a lockout rather than a pilot that simply won't hold.
The circulator pump moves hot water through the distribution loop, and after months of low or no demand over summer, it's not unusual for one to seize slightly or develop a noise on restart in the fall. A pump that's humming but not moving water, or that's leaking at the seal, generally needs replacement rather than repair.
A failed circulator often shows up as uneven heat — some radiators or zones warm while others stay cold — which can also be caused by an air-bound loop or a stuck zone valve, so a technician will typically check all three before concluding it's the pump.
Atmospherically vented Laars boilers depend on a properly drafting chimney. Blockage from debris, a bird's nest, or corrosion inside an aging metal flue can trigger a safety shutdown designed to prevent exhaust gas from spilling into the home — this is the system working as intended, not a fault to bypass.
| Symptom | Likely category |
|---|---|
| Pilot won't stay lit | Ignition system (thermocouple or flame sensor) |
| Boiler shuts down repeatedly, chimney area | Venting blockage or draft issue |
| Some radiators cold, others warm | Circulator, air-bound loop, or stuck zone valve |
| Banging or kettling noise | Heat exchanger scale |
| System losing pressure over weeks | Slow leak or failing expansion tank |
A boiler that needs its pressure topped up every few weeks has a leak somewhere in the loop, even if it's too slow to see — common spots include the relief valve, pipe fittings, and the expansion tank itself if its internal bladder has failed. Ignoring this eventually leads to air getting pulled into the system, which causes noise and uneven heating.
Kettling or banging noises point toward scale buildup on the heat exchanger, particularly in systems that have had frequent makeup water added over the years, since fresh water carries more dissolved minerals than water that's stayed in a closed loop.
Safety note
If you ever smell gas anywhere near a boiler, water heater, or gas line, leave the home right away and call FortisBC's emergency line at 1-800-663-9911 from a safe location outside — don't flip switches, light a match, or try to find the leak yourself. Gas boiler and water heater work, including venting changes, combustion adjustments, and gas line connections, must be performed by a Technical Safety BC licensed gas fitter.
A worn thermocouple is the most common cause on standing-pilot models, and it's a relatively simple, inexpensive repair for a licensed gas fitter.
This is often called kettling and usually points to scale buildup on the heat exchanger, which is worth having assessed before it causes more significant wear.
This is commonly a circulator pump issue, an air-bound loop, or a stuck zone valve, and a technician can narrow it down during a visit.
It can be a safety control doing its job in response to a venting or draft problem. Don't attempt to bypass or reset it repeatedly — have it assessed by a licensed gas fitter.
A slow leak somewhere in the piping, fittings, relief valve, or a failing expansion tank bladder is the usual cause, and it should be traced rather than just topped up repeatedly.
Most circulator failures are addressed with replacement rather than repair, since the pump is a relatively self-contained component.
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