Why Does the Prime Button on My SUNSUN HW-304B Not Draw Water?
Exact model: SUNSUN HW-304B
Safety: Disconnect the relevant power source and isolate moving, hot or pressurized components before service.
A.
Start with the accessible checks
What this suggests: A dry inlet hose after pumping the blue primer can mean an incomplete siphon, a leaking inlet valve-block seal or a failed primer-plunger seal; it does not by itself prove the button is broken.
What to do
- With the filter unplugged, establish the tank intake-to-IN and OUT-to-return connections, open both valves and ensure the canister sits below tank water level.
- Prime until the inlet hose holds a continuous water column.
Still not fixed? Continue to the next check.
↑ Back to the repair pathsB.
If the problem remains after the first checks
What to do
- If it will not hold, remove and clean the tap block and its two underside O-rings; replace split, flattened seals or an air-leaking hose.
- Inspect the blue button for sticking, tilting and water around the plunger.
- A documented HW-304B owner repair involved a loose plunger retaining ring, but opening its wet electrical head is service work, not an approved generic owner procedure.
Confirm the repair
The siphon remains established and the pump circulates without repeated priming. Do not energize a dry filter as a test.