Heater fails to start.


New member
May 11, 2022
I have a Hayward H300FDN that is failing to go into start mode.
The unit worked last week and got the pool up to temp. I saw that it was leaking from the heat exchanger a bit and ordered a replacement exchanger. I let the heater run for a few days with the dripping while waiting for the part. A few days in the heater stopped igniting. It did not even attempt start and no error code. If I set it to heat the blower does not come on. I could hear relays on the control board going through a clicking pattern, It ran through the pattern a few times and would switch to the off mode but the clicking pattern continued even when off.

The heat exchanger arrived today and was installed. Everything is back together. I verified all connections are made and water is flowing through the heater.

The heater is acting the same. The blower does no start but the relays are clicking. This is a fairly new unit. The heat exchanger required replacement because I let the PH get out of hand last year.

Does anyone have thought on what to check?

Thank you!


New member
May 11, 2022

The panel appears to work fine. I can raise and lower the setpoint or turn the unit off. In all settings, pool, spa and off it goes through the relay sequence.

It also goes through the relay sequence when there is no flow and the pressure switch opens. I also verified that with flow while its going through the relay sequence there is no voltage at the blower motor terminals. I can't relate the leaking heat exchanger to this problem but a few days after it started leaking it started acting like this.

The blower motor spins free by hand.


Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
Palm City/FL
Pool Size
Salt Water Generator
SWG Type
CircuPool RJ-30 Plus

This sounds like a bad flow switch or possibly a bad connection that may have been precipitated by the leak. I'm pretty sure you should not go through the ignition sequence with no flow. Check the switch to see if its state changes with flow. This may not be the only problem but the switch sounds like it is stuck in one position. I'm not as familiar with Hayward heaters so I'll ask others to help. @swamprat69 @ajw22 @1poolman1.

I hope this helps get you a helpful answer.

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