Most low pressure on a rainwater system comes down to a loaded filter, a flat pressure tank, a struggling pump or a low tank. Here's how to tell which.
Low pressure is one of the most common calls we get. Most causes are simple, and the order you check them in matters. Start with the cheapest, most likely fix and work back toward the pump.
If only one faucet or shower is weak, the problem is almost always at that fixture: a clogged aerator or showerhead. Unscrew it and rinse the screen. Rainwater is soft, so you won't see the mineral scale you'd get from well water, but fine sediment that slips past a worn filter collects there.
A loaded sediment filter is the most common cause of whole-house pressure loss. If your system has gauges before and after the filter housings, compare them with water running. A fresh cartridge shows only a few psi of difference. When the gap climbs toward 8 to 10 psi, the cartridge is choking the flow. No gauges? Look at the cartridge. If it's been in more than a few months or it's dark with debris, swap it and see if pressure comes back. Here are five signs your filters need changing early.
Open a tap and listen. On a pressure-switch system, the pump should kick on, run steadily, and shut off a little after you close the tap. If it clicks on and off every few seconds while water is running, that's short cycling, and the usual culprit is the pressure tank.
The pressure tank holds a cushion of air that keeps pressure steady between pump starts, and that air charge leaks down over time. To check it, turn off power to the pump, open a faucet until the pressure is gone, then put a tire gauge on the air valve on top of the tank. It should read about 2 psi below the pump's cut-in pressure, so about 38 psi on a 40/60 switch. If water comes out of the air valve, the bladder has failed and the tank needs replacing. Variable-speed pumps have their own precharge setting, so check the manual for those.
If pressure sputters, or the pump runs but can't build pressure, check how much water is in the tank. When the level gets very low, the pump can start pulling air. A pump that has lost its prime runs without moving much water, and many variable-speed pumps will throw a dry-run fault and shut down to protect themselves. If the tank isn't low, the usual causes are an air leak on the suction side or a sticking check valve.
If you've changed the filters, the pressure tank checks out, and pressure is still low, or the pump keeps short cycling, losing prime or throwing faults, it's time for a service visit. A pump that runs that way wears out fast, and the pump is the most expensive part of the system to replace. Call (512) 829-5800 or request service online. We work on any brand and any installer's system.
Questions about your system? Call Dripping Rainwater at (512) 829-5800.
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