The CE code is showing on screen

SOURCE: h400 pool heater showing a CE code on the display

I agree with this solution. I had a CE error so I took the cover off and used a hairdryer. It went back and forth from OK to CE (as it dried, I guess) but after five or ten minutes it stayed OK. I noticed that the rubber gasket around the display wasn't exactly tight so I'm thinking about reinforcing it. I'm also seriously thinking about building a small VENTED roof over the whole unit because it sure does seem to be susceptible to elements. And also, seal all openings to your heater! I had a mouse crawl up into mine over the winter and literally chew on the motherboard, ruining it. $200 to fix, thank you. NOT covered by warranty either.

SOURCE: Hayward H400 heater won't light and service light

This is a code for what is called a prover switch. What it is a circut for the air pressures. Depending on model you can have one or two of these. Their will always be one for the exaust perssure and this will often be the culpret. If the sensor is good a sooted exchanger, rat nests on the exchanger or in the exaust can cause this. If you have a second switch it will be for burner air pressure and you will look for the same problems only inside the burner cabnet. Good luck, I'm sorry I can't be more help. But at least you know to look to the vent system.

SOURCE: I have a hayward h400 heater; I just replaced the

Hi, "IF" code is Ignition Failure error. A number of parts can cause this error.
Now if you are the handy type and know how to use a Multi Meter you can try to diagnose the problem. You must know your limits, these heaters can be very dangorus and working with them should not be take light heartily. Know when to call a qualified person.
That said if you want to go forward follow these steps. 1. Ensure gas supply shutoff valves are open. Ensure that main gas shutoff installed adjacent to heater is open. Ensure that knob on gas valve inside unit is in on position. If OK, proceed to step 2.
2. Check for low gas supply pressure. Ensure inlet gas supply pressure exceeds minimum valve indicated on rating plate. If OK, proceed to step 3.
3. Check for faulty flame sense wiring or connection. Inspect flame sense wiring. Ensure wire harness terminals are securely fastened to flame sense and to control module. If OK, proceed to step 4.
4. Check for faulty gas valve wiring or connection. Inspect gas valve wiring. Ensure wire harness terminals are securely fastened to spade terminals on gas valve. If OK, proceed to step 5.
5. Check for gas valve failure or gas valve relay failure
A. Measure voltage across gas valve during trial for ignition. If 24 vac is present and gas valve does not open, gas valve is defective. Replace gas valve. B. If 24 vac is not present, gas valve relay on control module is defective. Replace control module.

SOURCE: Hayward H400 heater problem

LO usually indicates low water pressure. Check the pressure in your filter. You may need to backwash. If the filter is to clogged then the water pressure in the heater is so low that it won't activate the pressure switch. While checking the pressure turn the pump off and then on to make sure the pressure gauge is actually working. Also check the pressure coming out of the inlets into the pool. You should be able to tell if you have sufficient water pressure.

SOURCE: I have an H400 heater (H400IDL2) and I get the CE

CE is a communication error between the display board and the ignition board. If you've had a lot of rain lately it could just be that moisture inside the unit is causing the error rather than a bad board. Take the cover off and blast the inside with a hairdryer for a few minutes, making sure to get the boards and connecting wires. That sometimes clears the error.