No heat or hot water: Codes, Causes & Fixes

When a gas boiler gives no heat or hot water, the display usually shows why: low system pressure, an ignition lockout, a frozen condensate pipe on condensing models in cold weather, or a thermostat or timer that isn't calling for heat. Safe checks are limited to reading the pressure gauge, confirming the gas supply and other gas appliances work, checking thermostat settings and pressing reset once. If the fault returns, call a licensed heating technician; if you smell gas or a CO alarm sounds, leave the building and call your gas utility or 911.