Hayward Vent setup

May 14, 2025
12
Bryn Mawr, PA
Pool Size
30000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
So we just moved into a house with a pool. It has a pool house (indoor installation) with a Hayward H400FDN heater.

The heater is just not functioning properly. It seems very prone to throwing the “Lo” error, and even when I can get the pump to give it sufficient flow, the heater will fire up, something that sounds like a fan starts inside, and then I hear it ignite and the green “heat” light comes on. Within a second or two, the heat light goes out, and the entire pool house fills immediately with the smell of gas, even if I turn off the gas line valve within seconds of the green light turning off.

They first said the ignition was bad, and then they said the flame sensor was bad, but now that it does seem to light but not stay on, now they’re saying that the vent is not installed properly and don’t want to come back until the vent is installed properly (they don’t do HVAC). There’s something called a “mushroom” hood on top of it, that then connects to a straight vent through the roof of the pool shed. They say that is incorrect and it needs to be straight because the heater has a fan on the inside of it that assists the venting. They think the mushroom vent renders the entire vent system too open and is pulling too much out of the system for it to stay on.

Thoughts?
 

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The troubleshooting manual says to test continuity on several other sensors/switches. Can somebody help me identify what the following switches are in the circuit that includes the vent pressure switch?
 

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Is this a water pressure switch? I found it behind the heater on a shelf. It doesn’t look like the one that is currently on the heater. How can I test if it is functional?
 

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