Hayward Pool Heater Not Heating: LO, HI, IF Error Fixes

Quick Answer

A Hayward pool heater not heating often indicates a flow issue or ignition failure marked by LO, HI, or IF codes. The most common fix is cleaning the filter or adjusting the bypass valve to ensure adequate water pressure.

When a Hayward heater throws LO, HI, or IF, most folks panic and think they need a whole new unit. Usually they don't. LO is almost always a flow problem, and I've seen it fixed with nothing more than a backwash and a valve adjustment. Ignore it long enough though and your high limit switch starts tripping from heat buildup, and that's when a simple fix turns into a $300 repair.

HaywardPoolheaterSeverity: moderateDifficulty: intermediate75% DIY Success

Time to Fix

15–90 min

Difficulty

intermediate

Parts Cost

$0 (no parts needed)

Tools Needed

Phillips #2 screwdriver, Flat-head screwdriver

Hayward Pool Heater Not Heating: LO, HI, IF Error Fixes

OK so here's the deal with Hayward heaters not heating. LO, HI, and IF are the three codes you'll see most often, and honestly, most of the time you're looking at $0-$150 to fix it yourself. I pulled three of these apart just last month and two of them just needed a filter cleaning. The third needed an igniter, which runs about $40 online. Pretty fixable stuff.

Common Causes

Dirty pool filter causing water pressure to drop below the 25 GPM minimum the pressure switch needs to close, which triggers the LO code and shuts down the call for heat.
Bypass valve opened too far, diverting flow around the heater instead of through it, so the pressure switch never sees adequate flow even with a clean filter.
Pool pump impeller clogged or worn out, dropping GPM below the heater's minimum flow requirement, usually shows up mid-season when the pump's been running hard all summer.
Flame sensor rod coated in oxidation or calcium deposits, so it can't confirm flame is present and shuts the gas valve after about 4 seconds, triggering the IF code.
High limit switch tripped from a previous flow restriction, latches open and won't reset until the water temp drops and you cycle power to the board.
Gas supply pressure too low or a valve partially closed upstream, especially common right after the gas company services the meter or a propane tank starts running low.

Symptoms You May Notice

Pool water stays cold even after the heater's been running or trying to run for an hour or more.
LO, HI, or IF flashing on the digital display, sometimes cycling through codes if you've got multiple things going wrong at once.
You hear the igniter clicking or sparking but the burner never actually lights, then it goes quiet and the error code pops up.
Heater fires up, runs for 30-60 seconds, then shuts off and won't restart without you cycling power at the breaker.
Barely any flow coming out of the returns when the heater's running, or your pump pressure gauge is reading way higher than normal.

Can you reset a Hayward poolheater to clear the NOT-HEATING code?

Turn the heater's power switch to off, then flip the dedicated circuit breaker off at the panel. Wait a full 5 minutes, not just 60 seconds. This lets the high limit switch cool down and the control board fully discharge. Flip the breaker back on, then the power switch. Set your desired temp at least 5 degrees above the current pool water temp and watch the display for 30 seconds to see if the same code comes back or if the heater fires normally.

Tools Required for Diagnosis

Phillips #2 screwdriverFlat-head screwdriverDigital multimeterFlashlight or headlampFine steel wool or 400-grit sandpaperAdjustable wrenchShort jumper wire (for pressure switch test)

Diagnostic Checklist

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

ComponentComponent Under Test

Expected Range40–90 ohms

ConditionIf Open (OL) or infinite, replace component.

Frequently Asked Questions

How much does it cost to fix a Hayward pool heater not heating?

Honestly depends on what's wrong. If it's a dirty filter and a valve adjustment, you're looking at $0. A new pressure switch is $15-25. Flame sensor cleaning is free if you've got steel wool. New igniter runs $35-50 online. High limit switch is $20-30. Gas valve is where it gets expensive, $150-250 for the part plus labor if you hire it out. I'd say 70% of the LO and IF calls I go on get fixed for under $75, usually a flow issue or a dirty flame sensor.

Can I bypass the pressure switch to test if that's causing the LO code?

You can temporarily jumper it with a short piece of wire to confirm your diagnosis, yeah. But don't run it bypassed long-term. That switch is what prevents your heat exchanger from cracking if flow drops while the burner's firing. A cracked heat exchanger is $500-1200 in repairs. Use the jumper to confirm it's the switch, then order the $20 replacement and swap it in. Takes about 10 minutes.

My Hayward heater fires up but shuts off after about a minute. What's happening?

That's almost always the flame sensor. The igniter lights the burner fine, but the sensor rod is oxidized and can't confirm flame is present, so the board shuts the gas valve as a safety measure. Pull the panel, find that thin rod next to the burner, and hit it with fine steel wool for about 30 seconds. Seriously, I've fixed this exact problem probably 40 times and half of those were just a dirty flame sensor. Free fix, five minutes.

Is the HI code on my Hayward heater dangerous?

The HI code itself means the safety system worked correctly. The danger was the overtemp condition that triggered it. So if you're seeing HI on the display, the heater already shut itself down safely. But you need to figure out what caused the overtemp before you reset and run it again. Nine times out of ten it's low flow from a dirty filter or a partially closed valve. Fix the flow issue first, then reset.

How do I know if my Hayward pool heater is worth repairing vs. replacing?

Hayward H-Series heaters last 10-15 years with decent maintenance. If yours is under 12 years old and the repair is under $400, fix it. If you're looking at a cracked heat exchanger or a failed control board on a 14-year-old unit, the math usually tips toward replacement. New H-Series units run $1,200-2,200 depending on BTU rating. Newer units are also significantly more efficient, so if your old one's been struggling for a couple years, the energy savings on a new unit can offset part of the cost over 3-4 seasons.

What does the IF code mean on a Hayward pool heater?

IF stands for ignition failure. The heater attempted to light the burner three times and couldn't confirm a flame any of those tries. Could be a bad igniter, a dirty flame sensor, or a gas supply problem. Start with the flame sensor, clean it with steel wool. Then test the igniter resistance with a multimeter, should read 40-90 ohms. If both of those check out, look at your gas supply and make sure all valves are fully open.

Models Known to Experience NOT-HEATING Errors

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

H150FDP, H200FDP, H250FDP, H300FDP, H400FDP, H100ID2, H200ID2, H400ID2

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 17, 2026