hayward heater throwing AC diagnostic code

[bostonbruins59]

When I attempt to fire up the Hayward propane heater it throws the AC diagnostic code after waiting 30-40 seconds.
I do not hear the fan start up and there's no attempt to to ignite. Its just silent.
I've power cycled and looked for obvious obstructions to no avail.
The heater had been working fine up until this happened a week ago. Any ideas?

 

[ps0303]

Which Hayward heater do you have?

 

[bostonbruins59]

I believe its the Hayward H250FD. Sorry for the late response as my daughter was hospitalized for a while.
I have replaced the display module since that helped in the past but did not help this time. I have found
that by power cycling the heater, disconnecting and reattaching the tube connecting the blower
and the blower vacuum switch, along with some random reconnecting various connections the heater will
sometimes fire. But subsequent attempts to restart the heater throw the AC code again. When shutting
off the heater another error code (sorry can't remember what it is) is thrown temporarily but eventually clears itself.

 

[Hayward Pool]

When the heater goes through the routine to fire, one of the things it does is to check the vacuum switch to make sure it is open Why, the vacuum switch is closed by the fan proving it works so if it is shown closed the code will appear. If the switch is closed there are two possibilities. One is a bad vacuum switch, or a bad main module. Here is the link for the manual.

http://www.hayward-pool.com/pdf/manuals/UniversalH-seriesLowNOx-HxxxFDService&Installation.pdf

 

[bostonbruins59]

The diagnostic code is HF when I turn off the heater if that is informative. It eventually clears itself but that is the code I referenced above when turning off the heater.