Suburban ST-42 On Demand Water Heater Vent Caps

What does the Suburban ST-42 on demand water heater vent cap do?

The vent cap covers the exterior exhaust opening of the Suburban ST-42 tankless (on demand) water heater, directing combustion gases away from the sidewall and keeping debris, insects, and rain out of the flue. It is a wear part; if yours is cracked, discolored, or missing louvers, replace it before running the unit again. Confirm your model number reads ST-42 before ordering, since vent caps from Suburban's SW-series tank heaters are not interchangeable.

How do I know if my vent cap needs to be replaced?

Look for heat discoloration around the louvers, hairline cracks in the plastic housing, missing screws, or soot buildup on the surrounding sidewall. A damaged vent cap can disrupt airflow to the burner and cause ignition faults or nuisance lockouts on the ST-42. If you are also servicing related components, our 10 gallon RV water heater collection covers tank-style units and replacement parts for owners running the older Suburban platforms.

Is the vent cap easy to install?

Yes. Most ST-42 vent caps mount with four exterior screws and a bead of sealant around the flange. Remove the old cap, scrape the previous sealant off the sidewall, dry-fit the new cap, then bed it in Dicor or comparable lap sealant before driving the screws. Plan on 15 to 20 minutes. Keep the heater off until the sealant has skinned over.

What else should I check while servicing the vent area?

While you have the cap off, inspect the burner tube for spider webs or wasp nests, check the gasket for compression set, and look at the surrounding wall for soft spots from past water intrusion. Owners doing a broader off-season service often pair this work with our RV winterizing kits so the heater and water lines are protected before storage. Need help confirming the right vent cap for your serial number? Text or call 817-984-1852.