Water heater

A water heater, comprising:

• a vessel provided with a burner having a downward combustion surface;
• a fan casing accommodating a fan for supplying a mixture gas of primary combustion air and fuel gas to the burner, the fan casing being in communication with the vessel;
• an annular packing connecting a first connection end surface at a downstream end of a first passage forming a downstream-side passage of the fan casing with a second connection end surface at an upstream end of a second passage forming an upstream-side passage of the vessel in an airtight state;
• and
• a check valve disposed near the upstream end in the second passage, wherein
• the check valve includes a flange portion extending outward around an entire circumference of an upstream open end thereof,
• at least one of the first connection end surface and the second connection end surface includes a first step portion configured to allow the annular packing to be fitted thereinto,
• the second connection end surface includes a second step portion configured to allow the flange portion of the check valve to be fitted thereinto, and
• the annular packing has an outer circumferential edge larger than a periphery of the flange portion of the check valve and an inner circumferential edge smaller than the periphery of the flange portion.