Hayward H300 Intermittent Start-Up

[aswetich]

For the last two years my Hayward H300 starts up intermittently when the temp of the water is lower than the setting. Last year I found that taking a wire off one of any of the safety temp sensors and putting it back on made it work for a while and then it would stop again.

I have a Hayward H300 Millavolt system that is connected to a Jandy Aqua link.

Symptoms:
1. When the Jandy calls for heat the heater does not fire.
2. With the Aqualink still connected to the Heater I jump the two TH terminals and she fires right up and stays running. If I turn the heater off with the Aqualink and try to start it again it wont fire. With the wires removed from the TH terminals a jumper across the terminals runs the heater until the jumper is removed.
3. With the two TH wires removed from the gas valve I have over 600mv's at the gas valve.(Across the TH terminals)
4. With the two TH wires removed from the gas valve and the Aqualink calling for heat the two wires have continuity between them.
6. With everything hooked up and the Aqualink calling for heat I tried jumping each safety sensor one at a time and she wont fire.
7. Thinking there might be a connection problem I removed all the blade connectors from the safety sensor wires and soldered the wires to the sensors. (Excluding the gas valve Connections)

 

[danpik]

For the last two years my Hayward H300 starts up intermittently when the temp of the water is lower than the setting. Last year I found that taking a wire off one of any of the safety temp sensors and putting it back on made it work for a while and then it would stop again.

I have a Hayward H300 Millavolt system that is connected to a Jandy Aqua link.

Symptoms:

1. When the Jandy calls for heat the heater does not fire.

Not sure on the Jandy as I have never dealt with one. It looks like these act as the thermostat control for the heater. You would have to check for continuity thru thre unit when it is "call for heat" mode. I suspect that this is not your problem but, won't rule it out. I see on the schematics for one I looked up that there are separate water probes to check for temperature.

2. With the Aqualink still connected to the Heater I jump the two TH terminals and she fires right up and stays running. If I turn the heater off with the Aqualink and try to start it again it wont fire. With the wires removed from the TH terminals a jumper across the terminals runs the heater until the jumper is removed.

There are three terminals on a milivolt gas valve. TH/TP, TP and TH. The powerpile should be connected to the TH/TP and the TP terminals and the thermostat on the heater should be connected to the TH/TP and TH terminals. (this is assuming there is no connections to the Jandy) A jump across the TH/TP and TH terminals will bypass all safety switches and thermostats in the system and supply direct power to the valve thus opening it. Again, I do not know how the Jandy is wired into this so I can not say for certain how you got it to work by jumping the two th terminals. ((edit) check for loose connections in this wiring loop.) I am going to guess that the original heater thermostat is out of the loop at this time.

3. With the two TH wires removed from the gas valve I have over 600mv's at the gas valve.(Across the TH terminals)

Idealy, the powerpile should be supplying 750 Mv to the TH/TP and TP terminals on the gas valve. 600 is usually enough for the system to work. I usually find that below 450-500 range is the failure point.

4. With the two TH wires removed from the gas valve and the Aqualink calling for heat the two wires have continuity between them.

OK, this is good and answers my thoughts in 1.

6. With everything hooked up and the Aqualink calling for heat I tried jumping each safety sensor one at a time and she wont fire.

all of the sensors in the system including the original thermostat are daisy chained one after another. Think of a string of switches. All have to be on for continuity if one is off then continuity is broken. If two are off then jumping across one will not restore continuity.

7. Thinking there might be a connection problem I removed all the blade connectors from the safety sensor wires and soldered the wires to the sensors. (Excluding the gas valve Connections)

Drastic, but eliminates the connections. However, it could still be a switch is not closing to complete the circuit. Get a hand full if jumper wires with alligator clips on the ends and start jumping across the terminals on the switches. I suspect you may have a flow switch or pressure switch that is not closing properly. Also, is the original thermostat still in the loop? If it is, make sure it is turned up all the way. Aslo, don't forget to jump across the terminals on it as well.

 

[aswetich]

I figured out what the issue was ! The two wires that ran into the Jandy Aqua link for the heater were lose on the control board.

 

[ps0303]

Good thing you found it without tearing it all apart and what not. You could have been chasing your tail in circles for a long time.