Hayward H250 Milivolt Not Firing

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  #1  
Old 07-24-14, 09:36 PM
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Hayward H250 Milivolt Not Firing

I have a Hayward H250 Milli volt pool heater that intermittently fires. I have followed the troubleshooting guide and it was unable to identified the problem. I have then tried my own troubleshooting strategy and discovered something not covered in the manual that I think will easily point out the problem to the right person. So here it is:

All safety switches, thermostat and high limit and temp limits seem to be functional and at above pool temp settings with pump on.

1st Step: Jump across TH terminals on gas valve and burner fires
2nd: Remove jumper across TH terminals and the burner remains lit and heater functions normally
3rd: If I disconnect any wire in the safety circuit or turn the on/off switch off, or thermostat below water temp the burner goes out as it logically should
4th: After reconnecting the wire back to its terminal or moving switch to on, or increasing thermostat back above water temp the burner remains off and will not re-light even though all conditions are theoretically the same and the circuit is clean.

This is very repeatable. I can re-jump the TH terminals and repeat for all safety switches. The issue is that the only way I can turn on the heater is to jump start it.

I believe it is the gas valve or the thermostat and I was hoping someone who knows could vote in.
 

Last edited by tboyflyer; 07-24-14 at 11:25 PM.
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Old 07-24-14, 10:02 PM
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Welcome to the forums.

I believe it is the gas valve or the thermostat and I was hoping someone who knows could vote in.
Voting in sir and no..... it's not likely to be the thermostat or the valve. This is a millivolt system. There is a little silver tube that sits in the pilot flame. It's called the pilot generator. It generates the voltage to run the pilot valve and the main gas valve.

You will need to get a voltmeter to check its output. It should be close to 750millivolts which is just under one volt. You'll probably find it low. You more than likely have an issue with the pilot flame. Could be as simple as a spider web or clogged orifice.
 
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Old 07-25-14, 10:26 AM
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You may be on to something but still not cut and dry. Checked the voltage an it hovers around 500mV. sometimes up to 600. I removed the pilot assembly and cleaned the gas outlet which looked fine and re-assembled. I also added some dielectric grease to the connections of the thermopile to the gas valve to optimize the connection.

If I check the mV with the heater in the switched off or thermostat set below water temp i get a pretty solid 550-650mV. As soon as I switch it to on or turn the thermostat to above water temp the mV drops to around 400mv. It is very repeatable. And I still have intermittent normal operation but mostly the burner will not ignite on its own. It will stay lit once I jump it until the pump, a switch or the water achieves desired temp and cycles off.

I thought the the 500mV was intended to maintain the pilot light not necessarily fire the ain burner?
 

Last edited by tboyflyer; 07-25-14 at 11:25 AM.
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Old 07-25-14, 01:02 PM
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That pilot generator produces the voltage to hold the pilot valve open as well as activate the main valve. You either don't have enough of a pilot flame to generate enough voltage or the pilot generator is weak and needs to be replaced. Usually it's the pilot flame at fault.

The system is basically self sufficient and doesn't require any outside power.

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  #5  
Old 08-02-14, 01:10 AM
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I agreePJMax. I just ended up replacing my pilot and high temperature sensors on my 400,000 BTU ED1 heater and al worked fine. One other thing to consider. My H4001 worked intermittently where I had to jump start the heater to get it to work but it would go off and on periodically. I ended up removing the burner assembly and soaked each burner tube in a rust removal solution. After scrubbing the burner tubes they looked like new, however I noticed three of the burner tubes were missing the flange located at the far end of the inner tube that insures gas flow is consistent throughout the entire burner tube. I replaced the three bad tubes and refurbished the burner assembly. After that the heater worked like new.

So a new pilot with the pilot generator along with refurbishing the burner tube assembly fixed all problems I had with the unit. By the way, by removing the burner assembly I had the opportunity to clean out the inside of the heater housing which showed signs of rust and corrosion. After cleaning out the rust and painting with a high temperature paint the inside of the heater housing looked brand new. Doing this every two to three years will add ten years to your heater life.
 
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