Pool Error Codes

Pentair ERR PS: Water Pressure Switch Open

When a Pentair MasterTemp or MiniMax NT heater shows ERR PS, its water pressure switch hasn't closed to confirm flow, so the burner won't light until it does.

medium severity

Applies to: Pentair MasterTemp 125/175/200/250/300/400 and MiniMax NT residential gas pool/spa heaters

What it means

Walk up to the equipment pad and the MasterTemp's display is sitting on ERR PS instead of a temperature. That's the control board's shorthand for water pressure switch open: a small mechanical switch plumbed into the heater's inlet or outlet header is supposed to close once it senses adequate flow, and right now it hasn't. Until that switch proves flow is present, the ignition sequence never starts — the fan doesn't spin up, the igniter doesn't glow, nothing happens beyond the code on the screen. It's a safety interlock doing exactly what it's built to do: refusing to light a burner over a heat exchanger that isn't full of moving water, which would scorch it in minutes. The good news for a homeowner standing at the pad is that this particular fault is almost always about flow somewhere upstream of the heater, not the heater itself, so it's one of the more DIY-friendly codes on this list.

Likely causes

In practice, ERR PS almost never means the switch itself is at fault on the first occurrence — it means the switch is doing its job and something upstream is genuinely restricting flow.

What you can check yourself

Work through these roughly in order — they're listed from most to least common cause.

  1. Confirm the pump is running and check that valves feeding the heater are fully open
  2. Clean/backwash the filter and clear the pump strainer basket
  3. Bleed air from the system at the filter air relief valve
  4. Clear the error and let the heater retry once flow looks normal
Call a professional if…

If flow is confirmed normal at the pad but ERR PS keeps returning, the pressure switch itself is likely bad and needs professional replacement.

Sources

Related reading

This site is an independent reference, not a substitute for a licensed pool professional. Gas pool heaters can leak carbon monoxide and cause fire; pump and heater electrical circuits carry mains voltage. Anything involving the gas line, burner assembly, or house wiring should be handled by a licensed technician or electrician.