The Pentair MasterTemp is one of the most widely installed pool heaters in the country, and E05 is one of its most frequent fault codes. E05 is a pressure switch fault — the heater's control board did not receive confirmation that the combustion blower is producing adequate airflow. Without that confirmation, the gas valve stays shut and no heat is produced. Here is how to diagnose and fix it systematically.
The MasterTemp uses a negative-pressure (vacuum) type draft switch. The combustion air blower must pull enough vacuum in the combustion chamber to close the switch before the ignition sequence can proceed. The switch is wired in series with the gas valve control circuit. If the switch doesn't close, the gas valve cannot open — no gas, no ignition, no heat.
The key difference between MasterTemp and some older Hayward units is that the MasterTemp uses a single pressure switch rather than a dual-switch arrangement. This simplifies diagnosis but means the single switch does more work.
The MasterTemp displays E05 on its two-digit LED display. On units with a full digital display (400HD model), you may see "Pressure Switch" spelled out instead.
Before touching anything, initiate a heat call and listen. The MasterTemp blower should spin up within 2–3 seconds of the heat call. You will hear a distinct fan sound from the combustion air intake. If you hear nothing:
If the blower runs but E05 persists, locate the pressure switch on the left side of the unit. Find the small rubber or silicone hose connecting the switch to the combustion chamber or blower housing. Inspect the entire length for:
Blow through the hose — it should pass air freely. Replace the hose if any defect is found. The hose typically costs under $5 at any hardware store in 3/16" ID rubber tubing.
Remove the hose from the switch barb fitting. Set your multimeter to continuity or resistance. Measure across the two switch terminals. The switch should be open at rest (no continuity). Now place your finger over the port and apply gentle suction — the switch should immediately click closed (continuity). If the switch fails to close, replace it.
The most common replacement is Pentair part 42001-0063S, though you should confirm against your model serial number.
Walk around to the exhaust vent termination. Common obstructions include:
Clear any obstruction and re-test. On horizontally vented units, strong sustained wind can also create enough back pressure to prevent switch closure — a wind deflector kit (available from Pentair) solves this.
The MasterTemp also has a combustion air intake (the louver on the front or bottom of the unit). If this is blocked by debris, enclosure walls that are too close, or poor installation placement, the blower cannot pull enough air to produce adequate draft. Confirm the unit has at least 12 inches of clearance on all sides per Pentair installation requirements.
| Component | Part Number | Typical Cost |
|---|---|---|
| Pressure Switch | 42001-0063S | $18–35 |
| Blower Motor Capacitor | Varies by model | $8–15 |
| Combustion Blower Assembly | 42001-0052S / 0053S | $120–180 |
| Pressure Switch Hose (3/16" ID) | Generic | $3–8 |
Warning: Never bypass the pressure switch. E05 exists to prevent operating the combustion chamber without adequate airflow — without draft, combustion products including carbon monoxide can backdraft into the equipment area.
You can look up the Pentair MasterTemp E05 wiring diagram and pressure switch specifications instantly in PoolLens — even with no cell signal at the equipment pad.
PoolLens is a free offline PWA for pool service techs. Pentair MasterTemp, IntelliCenter, and IntelliFlo error codes all in one place — no login, no subscription.
Open PoolLens Free →E05 on a Pentair MasterTemp means the pressure switch did not close during the heat call. The heater's safety circuit requires proof of adequate combustion air draft before allowing the gas valve to open.
Press and hold the Mode button for 3 seconds, or power-cycle at the breaker. The fault will return immediately if the root cause is not fixed.
Yes. Sustained high winds can create back pressure at the flue termination, preventing adequate draft. This is more common on horizontal vented installations. A flue cap or wind deflector may help.
On most MasterTemp models, the pressure switch is located on the left side panel near the blower assembly. It has a small rubber hose connecting it to the blower housing and two push-on electrical terminals.
The most common MasterTemp pressure switch is Pentair part 42001-0063S. Confirm against your specific model year — the PoolLens app lists part numbers by BTU rating and model year.