Technical heating guide
Boiler Lockout Diagnostics
A lockout is a result, not a diagnosis. The cause may involve ignition, flame proving, gas pressure, venting, condensate, controls, sensors, flow, or a safety circuit.
Safety: Do not open gas-fired equipment, alter gas settings, bypass safeties, or work inside electrical controls without the proper qualification. For a gas smell or CO alarm, leave and call the utility or 911 from outside.
Read the sequence, not only the code
The fault code narrows the starting point, but the operating sequence shows where the boiler stops: pre-purge, ignition, flame proving, modulation, water circulation, or shutdown.
Intermittent lockouts need evidence
A reset may temporarily restore heat without correcting the cause. Fault history, live sensor values, flame signal, combustion, pressure, condensate, and wiring condition help identify intermittent failures.
Avoid repeated resets
Repeated resetting can hide a developing safety or combustion issue. Record the code and call for service when the lockout returns.
What to send before the visit
- Clear photo of the rating plate and model number
- Photo or exact wording of any error code
- Whether the issue affects space heating, hot water, or both
- When the problem started and whether a reset temporarily restores operation
- Your city and preferred service timing
Need service? Call 647-699-2474 or use the request form. Heating Experts will confirm the diagnostic visit and review repair pricing before approved work begins.
Technical service standards
Technical resources
Understand the system before approving the repair.
Use our knowledge hub for plain-language explanations of boiler lockouts, pressure problems, hydronic flow, combustion testing, condensate faults, OEM parts, and maintenance planning.