Lochinvar Flow Switch Open: Flow Switch Open / Low Flow
What the Lochinvar Flow Switch Open fault means, what causes it, and why it's a job for a licensed BC gas technician — not a DIY reset.
Severity
High — needs prompt professional attention
What the Lochinvar Flow Switch Open fault means
The flow switch did not confirm adequate water flow, so firing was blocked to protect the heat exchanger.
On Lochinvar Knight, WHN and SMART System series, Flow Switch Open is a water-flow / circulation fault. It is a protective response — the boiler is telling you something needs attention, and the safe, lasting fix is a proper diagnosis rather than repeated resets.
Symptoms you may notice
- No or weak heat
- Overheat or flow faults under load
- Pump running but rooms stay cold
Common causes of Lochinvar Flow Switch Open
Why this is not a DIY fix
Low-flow and circulation faults stem from a failing pump, trapped air, a stuck valve, or a blocked strainer. A technician measures actual flow and finds the restriction rather than masking it — protecting the heat exchanger from overheating.
In British Columbia, gas work must be performed by a TSBC-licensed gas fitter. GasBoilers.ca — a CanroHeat division — sends Red Seal–certified, gas-licensed technicians who diagnose the true cause, repair it correctly, and verify safe operation before they leave.
How our technicians diagnose & repair it
- 1Test circulator-pump operation and speed
- 2Purge trapped air and check for air-bound zones
- 3Inspect zone/mixing valves and strainers for blockage
- 4Confirm correct flow rate and stable temperatures
Related Lochinvar codes
Lochinvar Flow Switch Open — FAQ
What does the Lochinvar Flow Switch Open fault mean?
The flow switch did not confirm adequate water flow, so firing was blocked to protect the heat exchanger. On Lochinvar Knight, WHN and SMART System series, this is categorised as a water-flow / circulation fault.
What causes Lochinvar Flow Switch Open?
The most common causes are: Pump fault; Air-bound system; Closed valve; Blocked strainer. A licensed technician confirms which one applies before any part is replaced.
Can I fix Lochinvar Flow Switch Open myself?
No. Low-flow and circulation faults stem from a failing pump, trapped air, a stuck valve, or a blocked strainer. A technician measures actual flow and finds the restriction rather than masking it — protecting the heat exchanger from overheating. Repeatedly resetting the boiler without fixing the root cause can be unsafe and can cause further damage. Call GasBoilers.ca at 604-359-1081 for a licensed diagnosis.
Is the Lochinvar Flow Switch Open fault dangerous?
This is a protective fault — the boiler has shut down a function to protect itself. It is best diagnosed promptly by a licensed technician so the underlying cause does not lead to a more expensive failure.
How much does it cost to fix Lochinvar Flow Switch Open in Greater Vancouver?
Cost depends on the root cause and any parts needed. We start with a flat-rate diagnostic, then quote the repair before any work begins — no surprises. Call 604-359-1081 for current pricing and same-day availability.
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Licensed, Red Seal–certified gas technicians across Greater Vancouver. Upfront pricing, same-day service available.