20 Most Recent Hayward H400FDN Low NOx Natural Gas Pool or Spa Heater Questions & Answers

Possibly bad control board or a bad connection, need a little more info and I only have my phone to answer questions so I don't see the type of heater your posted under if you did.

you may need a new control board. sounds like a button is not registering

this indicates a communication error between the heater and control module. it may be as simple as disconnecting the main power to both the heater and control module to reset system. be sure to allow enough time for the system to 'forget'. usually 1 minute is fine.

"LO" is simply informing you that the Heater is not sensing proper water flow through it! A Flow Problem. A special sensor, called a pressure switch is this source. But... That does not mean it is bad - No, it is in most cases just doing its job! Most common reason - Dirty Filter. A good cleaning of the cartridges, or maybe a breakdown and recharge of a DE Filter, or a good cleansing backwash of your sand filter, will remedy this situation. Or... Check for any OTHER reason or situations water flow may be reduced through the heater:

• enough water in pool or spa?
• If you have a weir gate in skimmer, is it stuck in the UP position?
• Are any valves closed?
• Do you have a bypass valve at the heater?
  • If open, this will reduce the amount of water going thru heater, close it to the point, LO goes away.
• Could be debris in front of Pressure Switch, in the copper tubing
  • Unscrew and remove pressure switch, turn pump on. But first, align end of tube so that when water squirts out it will shoot out from heater and not onto electronic heater components!
• If all above is good, you may have failed pressure switch?
• Etc

Good Luck - hope this helped.

"LO" is simply informing you that the Heater is not sensing proper water flow through it! A Flow Problem. A special sensor, called a pressure switch is this source. But... That does not mean it is bad - No, it is in most cases just doing its job! Most common reason - Dirty Filter. A good cleaning of the cartridges, or maybe a breakdown and recharge of a DE Filter, or a good cleansing backwash of your sand filter, will remedy this situation. Or... Check for any OTHER reason or situations water flow may be reduced through the heater:

• enough water in pool or spa?
• If you have a weir gate in skimmer, is it stuck in the UP position?
• Are any valves closed?
• Do you have a bypass valve at the heater?
  • If open, this will reduce the amount of water going thru heater, close it to the point, LO goes away.
• Could be debris in front of Pressure Switch, in the copper tubing
  • Unscrew and remove pressure switch, turn pump on. But first, align end of tube so that when water squirts out it will shoot out from heater and not onto electronic heater components!
• If all above is good, you may have failed pressure switch?
• Etc

Good Luck - hope this helped.

Using a manometer, check the manifold gas pressure during start up. Does it go up to about 3" WC? If so, bleed the air out of the line until you get a strong smell of gas and try again.

If you are not getting any gas pressure you will need to check the power coming to the gas valve. Are you getting 24V at any point during the start up process? If so, the valve is bad and needs to be replaced. If not you will need a new control board.

John

What do you mean? Burners DO already have holes in them! that is how the raw fuel leaves the burners to be ignited. What is happening with the heater, that is making you ask a question for help? you may be using wrong terminology? Do you possibly mean - heat exchanger, tube bundle or heater coil?

What do you mean? Burners DO already have holes in them! that is how the raw fuel leaves the burners to be ignited. What is happening with the heater, that is making you ask a question for help? you may be using wrong terminology?

I find it highly unlikely that the burner has a hole. It does happen that there might be a crack in the burner manifold but it would be the first time I have ever heard of this. If you are referring to the heater core that the water passes through, the most likely cause is improperly balanced water. One of the first things mentioned in the owners handbook is to make sure that you balance the water. The only way to repair this is to replace the core.

Water Temperature Sensing Error A) Inlet water temperature sensor is reporting a temperature in excess of 104 degrees. Normal operation resumes 2 minutes after inlet water temperature sensor reports temperatures of 104 degrees or less. This error functions in both normal and remote thermostat modes. or B) Inlet water temperature sensor is reporting a temperature change at a rate faster than 6 degrees in 60 seconds, indicating a potentially damaging low water flow condition. Normal operation resumes when temperatures stabilize. If this condition is detected 3 times, the heater will lock-out until the electrical power is cycled off and back on.