Pentair Pool Heater E05 Error Code: Pressure Switch Open

Quick Answer

Pentair MasterTemp E05 means the pressure switch remained open, signaling water flow through the heater is below the required minimum. The four main causes are low water flow from the pool pump, a partially open bypass valve diverting water away from the heater, a clogged heater inlet screen, or a failed pressure switch. The MasterTemp 400 requires 20 to 25 GPM minimum.

PentairPoolheaterSeverity: highDifficulty: intermediate82% DIY Success

Time to Fix

30–120 min

Difficulty

intermediate

Parts Cost

$10 – $60

Tools Needed

Multimeter, Pool pressure gauge

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What Does the E05 Code Mean?

E05 means the heater pressure switch stayed open - water flow through the heat exchanger is too low or the switch itself has failed.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Low water flow through heater - pump undersized or underperforming40%

Heater bypass valve partially or fully open24%

Clogged heater inlet strainer screen14%

Failed or stuck pressure switch12%

Dirty pool filter raising backpressure and reducing flow10%

Symptoms You May Notice

E05 displayed on LED panel
Heater ignites briefly then shuts down
Heater will not light at all, shows E05 immediately
Repeated E05 lockouts after reset

Can you reset a Pentair poolheater to clear the E05 code?

After correcting the water flow issue or replacing the pressure switch, perform a soft reset: press ON/OFF, wait 30 seconds, then press ON. If E05 returns after the first heat cycle, repeat the flow diagnostics - the pressure switch will not close until adequate GPM is sustained throughout the heat cycle.

Tools Required for Diagnosis

MultimeterPool pressure gaugeScrewdriver setChannel-lock pliers

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Check pool filter pressure gauge

Check pool filter pressure gauge. If it reads more than 10 PSI above clean baseline (typically above 20 PSI), the filter is restricting flow.

Locate the heater bypass valve (typically a 3-way valve near the

If using a variable-speed pump

Remove the heater inlet strainer screen (typically behind the

With the pump running at heating speed

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name	OEM Number	Estimated Price
Pressure switch42001-0060S · $25–$60	42001-0060S	$25 – $60
Inlet strainer screen42001-0091S · $10–$20	42001-0091S	$10 – $20

Verify part fitment for your Pentair model

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs

Labor Approach

Our Verdict

REPAIR

Estimated Cost: $35 (Parts) vs $3000 (New Machine)

Frequently Asked Questions

What does E05 mean on a Pentair pool heater?

E05 means the pressure switch stayed open during a heat attempt, which tells the heater that water flow through the heat exchanger is insufficient. The heater locks out to prevent the heat exchanger from overheating and cracking.

How do I fix E05 on a Pentair MasterTemp?

Start with the three most common causes in order: clean the pool filter if pressure is above 20 PSI, fully close the heater bypass valve, and confirm your pump is running fast enough to deliver 20 to 25 GPM. If flow is confirmed adequate and E05 persists, test the pressure switch with a multimeter and replace it if it does not show continuity.

What is the minimum flow rate for a Pentair MasterTemp 400?

Pentair specifies 20 to 25 GPM minimum for the MasterTemp 400. Variable-speed pump owners need to set a dedicated high-speed schedule for heating mode - low-speed operation typically does not generate enough flow.

Can a bad pressure switch cause E05 even when flow is fine?

Yes. The pressure switch is a mechanical device with a diaphragm and contacts that can fail in the open position. If you have confirmed adequate water flow and the bypass valve is fully closed, test the switch terminals with a multimeter. A switch that stays open under adequate flow needs replacement.

Is E05 the same as ERR PS on Pentair heaters?

They indicate the same underlying fault - a pressure switch that did not close - but they appear on different model interfaces. E05 typically shows on the MasterTemp LED panel, while ERR PS appears on models with IntelliFlo integration or the newer digital display interface.

Related Pentair Poolheater Error Codes

Code: HUBPentair Pool Heater Error Codes Guide Code: ERR PSPentair Pool Heater ERR PS Error Code: SERVICE-HEATERPentair Service Heater Light Code: RESETHow to Reset a Pentair Pool Heater

Same Fix on Other Brands

Hayward poolheaterIF: Hayward Pool Heater IF Error Code

Models Known to Experience E05 Errors

This repair applies to most Pentair poolheaters with this error code. Common model numbers include:

MasterTemp 400, MasterTemp 250, MasterTemp 300, MasterTemp 125

Last verified for technical accuracy on March 14, 2026