Pressure problems

Isolating a loss of pressure can be a challenge. Once you've confirmed the high-pressure pump has plenty of unrestricted water flow, a pressure problem will come from one of three components:

1. The pressure control valve (needle valve)
2. The pressure relief valve (PRV)
3. The high-pressure pump

1. The pressure control valve

If mineral scale builds up on the needle and seat, the valve can't create the precise restriction needed to build pressure.

Inspect the needle

1. Loosen the cap nut directly behind the control knob.
2. Wind the knob all the way out until the needle assembly comes out of the valve body.
3. The needle should be clean and shiny. If it's coated in scale or debris, wipe it clean with a soft rag.

Clear scale from the valve body

1. Reinsert the needle assembly and tighten the cap nut until the knob's turning resistance feels familiar.
2. Wind the stem all the way in, then gently over-tighten the needle to crush the scale on the seat. Wrap the knob in a rag and use large pliers to turn it a fraction further, about 5 to 10 degrees.
3. Wind the knob all the way back out to fully open.
4. Run the boost pump for 5 minutes to flush the broken scale out of the system. While it runs, wind the valve in and out a few times to make sure the seat clears.

2. The pressure relief valve

The PRV dumps water overboard if the system over-pressurises. Its stainless steel spring relaxes over time, and eventually it can start dumping well below the 800 psi operating pressure.

The symptom: the system suddenly drops to around 200 psi while you're dialling in pressure. Winding the control valve further does nothing, but unwinding it fully and starting again lets pressure build briefly before it drops again.

Reset and calibrate the PRV

1. Plumb a temporary drain. Loosen the hose clamp on the PRV fitting. Disconnect the discharge line and plug it so water doesn't spill back out of the system. Run a temporary 1/2" hose from the PRV hose tail into a bucket, without a clamp.
2. Loosen the thin lock nut on the PRV, then wind the large cap nut all the way in until it bottoms out.
3. Start the watermaker as normal with the product water valve set to Sample.
4. With your helper watching the gauge, slowly bring the pressure up to 1050 psi.
5. Slowly loosen the PRV cap nut until the valve opens and the pressure drops. The needle may flicker before dropping sharply to under 200 psi.
6. With the system still running and dumping into the bucket, drop the pressure with the main control valve, then bring it back up. The PRV should now dump consistently somewhere between 950 and 1050 psi. Fine-tune the cap nut until it does.
7. Turn off the high-pressure pump, tighten the lock nut, remove the temporary line, then reconnect and tighten the original discharge hose.

There's a full PRV reset guide too.

3. The high-pressure pump

The pump is the least likely cause of low pressure. When it is the cause, it's one of two things.

Plunger seals

Plunger seals stop high-pressure water leaking past the ceramic plungers. They usually last for years, but running the pump dry, or without enough water flow, builds up heat that destroys them.

The symptom: water leaks or drips from the weep holes on the bottom of the pump, where the brass manifold meets the crankcase. If this is happening, the plunger seals need replacing.

Debris in the check valves

The pump has 6 check valves, an inlet and an outlet for each of its 3 plungers, behind the 6 hex-socket caps on the pump head. If debris or scale gets trapped between a valve's poppet and seat, it won't seal, and pressure drops sharply.

1. Remove a valve cap with a 3/8 inch Allen key.
2. With pliers, gently grip the small plastic tab on top of the valve cage and rock it upward to lift it out.
3. Inspect the valve. It should be clean and shiny. The poppet should lift off its seat easily, and the spring should snap it back smoothly.
4. If there's salt, discolouration or debris on the mating surfaces, clean it thoroughly in fresh water. An old toothbrush works well on the poppet and seat. Replacement valve kits are available, but a good clean usually solves it.
5. Look inside the valve chamber. Clean out any salt crust or scale, and check the O-ring at the bottom of the chamber is clean and undamaged.
6. Press the clean check valve firmly back into place and tighten the cap back down.
7. Repeat for the other 5 valves.