Hayward TriStar VS 950 Will Not Prime Or Keeps Losing Prime

What "Will Not Prime" Means Here

On the TriStar VS 950:

• Priming starts at the beginning of a run, usually at the maximum allowed speed.
• The pump expects to pull in water, push air out through the returns, and end up with a mostly solid water column.

If, after several minutes, the basket is still mostly air or the pump surges between water and air, it is not properly primed.

Step-By-Step Troubleshooting

Step 1: Confirm water level and valves

Owner-level:

1. Make sure water in the pool is at least halfway up the skimmer opening.
2. Ensure all relevant suction valves for that circuit are open.
3. Verify any cleaner valves are set where you expect.

If the water is low enough for the skimmer to pull air, fix that first.

Step 2: Check the lid and basket

1. Shut off the pump and relieve system pressure using the filter air relief.
2. Remove the pump lid.
3. Empty and rinse the basket.
4. Inspect the lid o-ring for cracks, flat spots, or debris.
5. Clean the o-ring groove and sealing surfaces, then re-install the o-ring and lid. Lightly lube if appropriate for the material.

A dry, dirty, or pinched o-ring is one of the most common priming problems.

Step 3: Refill, restart, and time the prime

1. Fill the pump strainer housing with water up to the suction outlet.
2. Replace and lock the lid by hand.
3. Start the pump and watch the basket for several minutes.

On this pump, priming is typically done at high speed for a configurable duration. If the prime ends and the pump drops to a low speed before the basket is full, you may need to increase the priming time or adjust speeds.

Step 4: Look for air at returns and in lid

While the pump is trying to prime:

• Watch the returns in the pool for a steady stream of bubbles, which indicates air on the suction side.
• Watch the clear lid. If you see constant air swirling in, not just an initial purge, you have leaking suction plumbing.

Key places air can enter:

• Suction unions at the pump.
• Valve stems on the suction manifold.
• Threaded plugs or fittings on the suction line.

Owners can visually inspect; techs should tighten, reseal, or replace fittings as needed.

Step 5: Check drain plugs and housing

1. With the pump off, inspect the drain plugs for missing or damaged o-rings.
2. Confirm the plugs are snug, but not overtightened.
3. Look for small drips under the pump while it is running; these can also be air entry points on the suction side.

If water can leak out at rest, air can leak in while running.

Step 6: Check for suction blockages

Tech-level:

1. Remove skimmer baskets and inspect ports for debris.
2. If there is a vacuum port, check the cover and the line.
3. If you suspect a blockage, use a drain king or similar hose bladder to backflush the line from equipment back toward the pool.

You should feel strong suction at the pump lid with the pump running. A vacuum gauge at the lid can quantify this, but even by hand you should feel a strong pull.

Step 7: Confirm speed and priming settings

On the TriStar VS 950 Configuration menu:

1. Check MAX allowed speed and MIN allowed speed. If the max is set too low, priming will be weak.
2. Check Prime Duration. If it is set to 0 or a very short time, the pump may never get a full prime before dropping back.

Owners can read these; techs should adjust based on plumbing layout and lift.

Common Parts That Fix This Problem

• New lid o-ring when the existing one is cracked or flattened.
• New drain plug o-rings when plugs seep.
• Union gaskets if suction unions drip or pull air.
• In rare cases, diffuser or impeller if damaged and unable to draw suction properly.

Model-Specific Notes

• The TriStar VS 950 can sit above or below water level, but higher installations need a solid priming routine and tight plumbing.
• This pump's internal priming routine can run at the maximum allowed speed for up to several minutes. Take advantage of that for long suction runs.
• The quieter operation at low speed makes it easy to miss a marginal prime. Always look at the lid, not just listen.

How To Prevent Recurring Priming Issues

• Keep the pool level stable and educate owners about evaporation and auto-fill.
• Replace lid o-rings on a regular schedule, not just when they fail.
• Use proper thread sealant (PTFE tape, not pipe dope) on molded plastic fittings.
• Avoid unnecessary suction fittings and restrictions that make the pump work harder.