Pentair UltraTemp Low Water Flow Alarm

The LOW WATER FLOW alarm on a Pentair UltraTemp heat pump indicates the water pressure switch is sensing insufficient flow through the unit. This is a protective feature that prevents the heat pump from operating without proper water circulation.

When this alarm appears, the red SERVICE light illuminates and the heat pump stops operating until the flow issue is resolved.

Common Causes

Circulation Pump Issues

• Pump not running or not on correct speed
• Pump running on too low an RPM (variable speed pumps)
• Pump impeller clogged with debris
• Pump not primed properly

Filter System Problems

• Dirty or clogged filter
• Filter pressure too high (needs backwash/cleaning)
• Filter pump basket clogged
• Skimmer baskets full

Plumbing Issues

• External bypass valve open (diverting flow around heat pump)
• Valves partially closed restricting flow
• Air leak on suction side
• Plumbed backwards (inlet/outlet reversed)

Pressure Switch Problems

• Pressure switch needs adjustment
• Pressure switch failed (stuck open)
• Debris in pressure switch connection

Troubleshooting Steps

Step 1: Verify Pump is Running

1. Check that the circulation pump is on
2. For variable speed pumps, ensure speed is adequate (minimum 30 GPM for UltraTemp)
3. Verify pump basket is full of water (pump is primed)

Step 2: Check Filter System

1. Note filter pressure gauge reading
2. If 8-10 PSI above clean baseline, service filter
3. Clean pump and skimmer baskets
4. For sand/DE filters, backwash if needed

Step 3: Check Bypass Valves

1. Locate any external bypass around the heat pump
2. Ensure bypass valve is fully CLOSED
3. Verify all isolation valves are fully OPEN

Step 4: Test Water Flow

With pump running, verify adequate flow:

• Minimum flow: 30 GPM (113.6 LPM)
• Maximum flow: 120 GPM (456 LPM)
• Look for good return jet pressure in pool

Adjusting the Water Pressure Switch

The pressure switch may need adjustment if flow is adequate but alarm persists:

To Increase Sensitivity (alarm triggers easier):

1. Turn off pump
2. Locate adjustment wheel on pressure switch
3. Rotate clockwise until LOW WATER FLOW alarm appears
4. Note the position

To Decrease Sensitivity (alarm triggers harder):

1. With pump running and good flow
2. Rotate adjustment wheel counterclockwise
3. Stop when alarm clears and service light goes off
4. Wait for time delay countdown

Verification Test:

1. Turn off pump
2. Verify LOW WATER FLOW alarm appears
3. Turn pump back on
4. Verify alarm clears

Testing the Pressure Switch

If adjustment doesn't resolve the issue:

1. Turn off power to heat pump
2. Locate pressure switch wiring
3. With pump running and good water flow, check resistance
4. Switch should be closed (continuity) with flow
5. Switch should be open (no continuity) without flow
6. If switch doesn't respond properly, replace it

Flow Requirements

Parameter	Value
Minimum Flow	30 GPM (113.6 LPM)
Maximum Flow	120 GPM (456 LPM)
Maximum Water Pressure	50 PSI (3.5 bar)

When to Call for Service

• Flow is verified adequate but alarm persists after adjustment
• Pressure switch wiring is damaged
• Heat exchanger appears clogged internally
• Unit was recently installed (may be plumbed incorrectly)