Hayward Heater wont stay on

Vintagestg

New member
Jun 11, 2020
1
St. Louis. MO
I have a Hayward H250FDN heater. It will start and heat the water but then shuts down after 60 seconds and displays the AO code. According to the manual this indicates a bad blower vacuum switch. I've checked everything suggested in the manual... the blower, vacuum switch, tubing between the blower and vacuum switch and all associated wiring. All appears to be working like it should. The only thing left would be the ICB. Before I spend $200 on a new one I thought maybe someone on this site may have an idea on something else I could check? Thanks in advance for any help.
 

swamprat69

Well-known member
Mar 30, 2019
271
Las Vegas, NV
To start with you will need to know whether the problem is with a failed pressure switch or in an area that is causing the pressure switch to do the job it is supposed to do. You will need a digital manometer in order to do this. You can physically check the tubing and connection points for blockages, but without the manometer you can't tell much else ( a manometer is also good for checking gas pressure ). Most but not all pressure switches have a set point marked on their label ( such as -.50"WC ). Using the manometer to check the pressure that is developed if the switch is labeled -.50"WC and you are reading -.65"WC and the switch is not closing, you have a bad pressure switch. If the manometer reads less than -.50"WC then the pressure switch is doing what it is supposed to do and you have to isolate the reason for the reduced pressure reading. This can be due to several things, i.e. blocked or partially blocked heat exchanger, dirt buildup across the cup of the blower wheel vanes, reduced motor speed due to failing bearings etc.
 

Pool Clown

In The Industry
Sep 5, 2008
2,136
Silicon Valley, CA
If you dont have a manometer, you can still check the air switch by hooking it up to your continuity meter and try to start the heater. You will need to disconnect system wires from the switch. The heater wont fire, but the blower should come on, for 15 to 30 sec. and it is at that point that you should check your meter to see if the switch closes. This is the only way to check the switch. Manometer will only give you a reading, and that is useful only if you have the spec at witch the switch is supposed to close (this may be marked on the switch).

Note:
You may be able to get a faulty switch to close if you suck (or blow) on it yourself, making that a skewed test.

Also, make sure that inside of the spigot or barb where the hose connects to the blower and also the switch is clear. Its a usual place for spiders, etc to make home.
 

swamprat69

Well-known member
Mar 30, 2019
271
Las Vegas, NV
Checking continuity at the pressure switch will only tell you whether or not the switch is closing. It will not tell you whether or not the switch is bad. If the pressure switch set point is .50"WC and you are only getting .40"WC the switch will not close, but it doesn't mean the switch is bad because it is not closing ( It would be doing the job that it is supposed to do ). Some furnaces use pressure switches that are not marked with a set point and the only way to troubleshoot them is to contact the manufacturer and get the set point for the pressure switch.
 

swamprat69

Well-known member
Mar 30, 2019
271
Las Vegas, NV
You must also be careful not to damage the diaphram in the pressure switch either when trying to clean/clear the barbed connection of the pressure switch or by blowing/sucking too hard as the diaphram is very thin and meant to handle only a small fraction of 1 PSI.