Start with the symptom, identify whether the problem affects space heating, domestic hot water, or both, and stop when the work requires combustion, gas, electrical, venting, or pressurized-system service.
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Stop and make the area safe: Leave or call emergency help for fire, smoke, gas or fuel odor, a carbon-monoxide alarm, shock, arcing, severe leakage near electricity, sewage exposure, or anyone becoming ill. Do not keep resetting unsafe equipment.
Accuracy first: Identify the exact model and use its current manufacturer instructions. Values described as typical are screening references, not universal pass/fail limits. Adopted codes, the equipment rating plate, and the exact service manual control. Review primary technical sources.
Optional field notes and technician handoff report
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Leave immediately and call for help for a gas or fuel-oil odor, a carbon-monoxide alarm, visible soot, melted or discolored venting, exhaust entering the building, flame rollout, severe water leakage near electrical equipment, or anyone experiencing headache, dizziness, nausea, weakness, confusion, or unusual sleepiness. Do not reset or continue operating the appliance.
Homeowner boundary: Use normal controls only. Do not remove the combustion cover, open electrical panels, adjust gas or oil components, bypass a safety, bleed a hot system, add chemicals, or repeatedly reset a locked-out appliance.
No heat anywhere
Confirm the thermostat is set to Heat and above room temperature.
Check the normal boiler service switch and the labeled circuit breaker once.
Read—not change—the display message, fault code, pressure, and temperature.
Confirm radiator valves normally left open have not been closed.
If one permitted reset does not restore normal operation, stop and request service.
Some rooms or one zone are cold
Verify that zone's thermostat is calling.
Make sure furniture and rugs are not blocking baseboard or radiator airflow.
Confirm accessible radiator valves are in their normal position.
Listen for unusual rushing, banging, or continuous water flow.
Report the affected zone and whether other zones work normally.
Combi has heat but no hot water
Try more than one hot-water fixture.
Confirm cold water flows normally at the same fixtures.
Record whether the boiler display changes when a hot tap opens.
Remove debris only from an accessible faucet aerator if cold flow is also poor.
Do not open the boiler; report whether demand was detected.
Hot water but no space heat
Check thermostat mode, setpoint, batteries, and schedule.
Determine whether every heating zone is affected.
Record the boiler display during a heat call.
Do not force zone valves or jump thermostat wires.
Request service with the thermostat and display information.
Low-pressure display
Photograph the pressure reading while the system is cool.
Look from a safe distance for visible water beneath the boiler, relief pipe, radiators, and exposed piping.
Do not continually add water; repeated pressure loss indicates a fault.
Use a manufacturer-provided filling procedure only if you understand the exact valves and the manual permits homeowner filling.
Stop if pressure rises rapidly, a relief valve discharges, or leakage appears.
Water leak or relief discharge
Keep people away from hot water and wet electrical equipment.
Do not cap or plug a relief discharge pipe.
If safe, turn the thermostat down and use only the normal appliance switch.
Photograph where the water originates and the pressure reading.
Arrange prompt professional service.
Frozen condensate suspected
Only inspect an exterior plastic condensate termination that is safely reachable from ground level.
Do not use a torch, boiling water, sharp tools, or disassemble internal traps.
Follow the exact appliance manual for permitted thawing.
If the pipe is damaged, repeatedly freezes, or the fault returns, request service.
Noise, banging, or kettling
Note whether it occurs during ignition, pump operation, heating, or shutdown.
Identify the affected zone and whether pressure changes.
Do not bleed a hot system or add cold water to an overheated boiler.
Shut the appliance down normally for violent banging, boiling sounds, or rapid pressure rise and request service.
Information to send with a technician request
Manufacturer, complete model number, and approximate age
Exact fault code and display wording
Cold pressure and operating pressure shown on the display or gauge
Whether space heat, domestic hot water, or both are affected
Which zones and fixtures are affected
Photos of the appliance, display, vent termination, and visible leak—never passwords or payment information