Troubleshooting Hayward H300 Milivolt Pool heater

[mgerety]

I have an old Hayward H300 milivolt pool heater that was already installed on my pool when I bought my house. It's worked intermittently on and off for the past few years. This year, I can get the pilot to light, but could not get the heeater to fire. I attempted taking off and cleaning all the contacts on the gas valve, power switch, thermostat, pressure valve, etc but to no avail.

The gas valve has 3 terminals: TH, TH-PG/PG. I found a suggestion online stating to try jumpering across the TH and TH-PG terminals on the gas valve. Lo and behold, when I jumper between them, the heater fires up. (see attached image)

The power swtich seems to work, becuase if I remove the jumper wire with the power switch off, the heater turns off in about a second. If I jumper the wires with the power switch on, it will keep running even if I remove the jumper wire, but will turn off when I turn off the power switch.

1. Is it safe to run it like this to bring my pool temperature up?
2. What is wrong? Is this just a thermostat problem? How would I got about fixing this?

Thanks in advance.

 

[kadavis]

What you have done is bypass all the safety switches,so if the pump turns off the heater will still run, if you have a overheating condition it will still run and it will run no matter what the temp is. If all your doing is raising the temp for a one time event this could work as long as the pump is on the whole time, if the pump goes off you will probably be left with a melted heat exchanger and worse. I don't recommend this. Try googling pool millivolt heater trouble shooting, there is several you tube videos on your heater