Raypak Heater Ignition Fault Tree (P-R Series and Avia)
Why this matters
Raypak P-R266A / P-R336A / P-R406A heaters and the newer Avia series (P/N 018034 for 264k BTU, 018035 for 333k, 018036 for 406k) are the most-installed residential gas pool heaters in the U.S. When they will not light, the customer's pool drops 5-8 degrees overnight and the service call is graded by how fast you isolate the fault. Working the ignition sequence in the order the heater itself runs through it puts the failed component under your fingertip in under 15 minutes, instead of swapping parts on a hunch. This tree applies to natural gas and LP P-R series with Honeywell S8910U or S8610U module, and Avia with the integrated 2-line LCD control board.
The ignition sequence (and where it stops)
A healthy Raypak ignition is six gated steps:
- Call for heat from thermostat or external automation (24 VAC at TH terminal).
- Pressure switch closes (water flow proven, around 1.5-3 PSI differential).
- High-limit closes (water temp below 135 F).
- Blower runs 30 seconds for pre-purge (Avia and 2018+ P-R only).
- Ignitor energizes; gas valve opens; flame establishes within 7-second trial.
- Flame sense rectifies the AC signal to DC microamps; module locks in.
Identify the step the heater hangs on, and the fault is identified.
Step 1 - Confirm call for heat
Set thermostat 10 degrees above water temp. Listen for the relay click on the control board. With a meter on TH to TR, you should read 24-28 VAC. No voltage: bad transformer (P/N 010253) or open thermostat. If using OmniLogic / IntelliCenter to call the heater, confirm the heater is set to Remote and the bypass jumper between TH-TR is removed.
If voltage is present but nothing else happens, jump to Step 2.
Step 2 - Pressure switch
The pressure switch (P-R series: 003903F; Avia: 014830F) closes when filter inlet pressure rises against the heater's bypass valve resistance. Common failures:
- Pump on but pressure switch open: bypass valve stuck closed, filter clogged, or pressure switch diaphragm ruptured.
- Pressure switch closed at idle: stuck shut from corrosion - replace.
Test: pull both wires off the switch and jump them with a clip lead. If the heater advances, the switch (or its calibration) is the fault. Do NOT leave the jumper in - it disables a code-required interlock per ANSI Z21.56.
On Avia, the LCD will display "PS OPEN" when the switch fails to close.
Step 3 - High-limit and stack flue switch
P-R series uses two manual-reset high-limits: one on the inlet header, one on the outlet. Reset button popped on either kills 24 VAC to the ignition module. Causes: low flow (algae-clogged filter), dirty heat exchanger, thermostat shorted, pump turned off mid-fire.
The roll-out (flue) switch trips on backdraft - usually a blocked top vent, downdraft into the cabinet, or a sooted heat exchanger. Resetting without finding the cause guarantees a callback.
If a high-limit has been resetting repeatedly, pull the heat exchanger and inspect the copper fin tubes. Soot on a clean-burning heater equals downdraft or undersized gas supply.
Step 4 - Pre-purge (Avia only)
Avia runs the blower for 30 seconds before energizing the ignitor. If the blower does not run, check 120 VAC at the blower harness (2018+ Avia uses an ECM blower with a 5-wire harness). The Avia LCD displays "BLOWER FAULT" or "PROVING SW FAULT" if the blower runs but the pressure-proving switch downstream does not close - usually a kinked pressure tube between the blower and the proving switch.
Step 5 - Ignitor and gas valve
The hot surface ignitor (P/N 007020F for P-R, 014812F for Avia) glows orange-white when 120 VAC arrives. Visually inspect through the sight glass:
- No glow: open ignitor (test continuity with the ignitor cold - should read 50-200 ohms; open = replace), or no 120 VAC at the orange wires (check fuses and S8910U module).
- Glows but no gas: gas valve fault, or gas valve is getting no signal. Honeywell S8910U pulses the valve at the end of ignitor warmup. Test 24 VAC across MV-PV at the valve terminals during the trial-for-ignition window.
- Gas valve clicks but no flame: gas supply problem. Test inlet pressure under fire: NG needs 4-10.5 inch w.c., LP needs 8-13 inch w.c. Below the floor, the valve will not hold open. The most common cause on new installs is a half-inch gas line where the heater needs three-quarter inch minimum at length.
Step 6 - Flame sense
Flame establishes but heater locks out 7 seconds later - this is a flame sense failure. The flame rod must rectify the AC signal to at least 1.5 microamps DC. Test with a meter on microamps DC in series with the flame sense wire.
Causes of low microamps:
- White oxidation on the flame rod - clean with fine emery cloth, not steel wool.
- Cracked porcelain at the flame rod base - replace rod (P/N 010306).
- Poor ground - the burner manifold must be electrically continuous to the cabinet ground.
- Flame rod not in the flame envelope - bent rod after a heat exchanger swap.
On Avia the LCD shows "FLAME LOSS" or "FALSE FLAME." False flame at startup (microamps reading with no flame) means a shorted flame rod wire.
Quick reference fault map
| Symptom | Most likely cause |
|---|---|
| No 24 VAC at TH | Transformer or thermostat |
| Pressure switch never closes | Bypass valve, filter, ruptured diaphragm |
| Trips high-limit on every fire | Low flow, dirty heat exchanger |
| Ignitor glows, no flame | Gas valve, gas supply pressure |
| Lights, runs 7 sec, drops out | Flame sense rod or ground |
| Random lockouts mid-run | Backdraft, roll-out switch resetting |
Do not jumper the high-limits, the pressure switch, or the roll-out switch as a "permanent fix." Each interlock is required by ANSI Z21.56 - bypassing them risks heat-exchanger rupture, downdraft CO release, or unburned-gas flash on relight. Jumper only momentarily to identify the failed component, then replace.
References
- Raypak P-R Series Installation and Operating Instructions, document 241406 Rev L (2023)
- Raypak Avia Installation and Operating Instructions, document 241876 Rev F (2024)
- Honeywell S8910U Universal Hot Surface Ignition Module Spec Sheet, document 69-1894-04
- ANSI Z21.56-2022 / CSA 4.7-2022 - Gas-Fired Pool Heaters
- NFPA 54 / ANSI Z223.1-2024 - National Fuel Gas Code, Sections 7 and 9
- Raypak Service Bulletin SB-22-04 - Avia Flame Sense Microamp Threshold