Too Little or Too Much Pressure: Why a Float Valve Won't Open

A float valve that won't let water through is usually blamed on the valve. Often the real cause is the pressure feeding it. Topaz, Megaflow, and Vortex valves are pilot-operated diaphragm valves, and they use supply pressure as part of how they work. That means the supply pressure has to be in the valve's rated range, not too low and not too high.

Why Pressure Matters

These valves use supply pressure to push the diaphragm back against its spring. When the float arm drops, it presses a start pin that relieves pressure from behind the diaphragm and lets water flow. Both parts of that depend on pressure being in range.

Check the Rating for Your Valve

• Topaz: 5–100 PSI (Standard and Industro); up to 150 PSI (Differential, Partfill, Compact)
• Megaflow: 5–150 PSI
• Vortex: 5–100 PSI (Standard and Bottom Fill); up to 150 PSI (Differential and Partfill)

If Pressure Is Too Low

The valve won't open. If there isn't enough pressure, the diaphragm can't move and no water flows. This shows up as a trough that never refills, even though the supply is on and the float is down.

Before blaming the valve, look at what's happening upstream: a partly closed shutoff, a long or undersized supply line, a clogged inlet filter, or a pump or well that can't hold pressure when the valve calls for water. Check pressure during a normal pump cycle, not just once at rest.

If Pressure Is Too High

The valve will still close, but it may not open again. Pressure that's too high can hold the float arm and ball up in the air, so the arm can't drop and the start pin never gets pressed. A telling sign: if you push the float ball down by hand, the valve opens, but once it shuts off, the same thing happens again.

How to Find Out Which One You Have

1. Put a pressure gauge at the valve and read it while water is flowing, and again when the valve has shut off.
2. Compare the reading to the range for your valve above.
3. If it's below the minimum, look for restrictions or supply problems upstream.
4. If it's above the rating, the supply pressure needs to be brought into range. A pressure regulator installed on the supply line ahead of the valve may solve the problem by bringing the pressure down.

When It's Something Else

If the valve opens but won't shut off, that's a different problem; see Why Your Float Valve Won't Shut Off. For other symptoms, our troubleshooting guide covers the ten most common. And if you're not sure what your pressure should be, contact us with your valve model and we'll help.