Gas pool heater questions

My pool heater is acting up this year. Once the pilot is lit, it stays lit. The thermostat works, in that I can hear it click as it is rotated past a certain point, and my meter shows that it is opening and closing with the click. The vast majority of the time, rotating the thermostat to the point of calling for heat, does NOT fire the burner. If I jumper the TH terminals, and get the burner started, then the thermostat usually takes over and lets the burner cycle off and on. But if the thermostat quits firing the burner, I have to jumper it again. Since the thermostat is wired to the pressure safety switch, I was thinking that maybe the pressure safety switch was going bad, but that is just a guess. Before I start replacing parts, I thought I's post here.
Can someone point me in the right direction? I'd appreciate any help/info.
Tim
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Checked the thermocouple?
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Richard J Kinch wrote:

I figured that the thermocouple was good, since it was letting the pilot stay lit, and would sometimes let gas flow. How can I test it - heat it up and see if it's voltage output changes?
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Easiest to have a spare and swap it in. Thermocouples are hard to meter for performance.
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You may have a stuck main gas valve. Is the valve 24 volt or millivolt?

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Tim,
Chances are that you have more than one issue to fix.
1) The thermocouple is heated by the pilot flame and produces current that activates the main burner valve. It's not uncommon to see reduced output from the thermocouple either because it is old, or because it is not getting hot enough (think low pilot, out of the flame, covered with ...stuff) etc.
2) As you observed, the thermocouple current is routed thru a pressure safety switch. Typically, after a few years, the silver contacts on this switch will tarnish. Since the switch itself is totally enclosed, you cannot observe this. You have two options:
a) Buy a new switch or,
b) get clever. Remove the entire switch from the heater (2 wires and a copper tubing fitting). Temporarily connect the switch leads to(in series, of course) a 12 volt automotive lamp and a 12 volt battery. The lamp should not be a headlight but one of the smaller lamps that pulls 1 or 2 amps. Usually a 1257 bulb is about right. Once connected, cycle the pressure switch a few times so the light flashes on & off. You may be able to blow into the pressure orifice or turn the pressure adjustment until the switch closes. After 7 or 8 cycles, put the switch back into the heater and fire it up.
You (and others here) may be asking why this procedure works. As it turns out, because the current switched by this pressure switch is so low, any contact resistance is significant. When the silver contacts tarnish, it raises their resistance. Connecting the switch to a heavier load (like the automotive bulb) causes the contacts to arc slightly which burns off the tarnish and...voila!
BTW, there is loads of technical info on most pool heaters, on the "Net". Just Google the brand name.

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Craven Morehead wrote:

Is there something in particular I'd be looking for when I look for a new switch? Would I be able to find one at Home Depot, or would I need to go to a specialty place? Thanks for all the help so far.
Tim
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Pool supply place like "Leslie's" (USA), or online.

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responding to http://www.homeownershub.com/maintenance/Gas-pool-heater-questions-119616-.htm tschaefer wrote: I have an identical problem. I am wondering what you found as your solution to this. I just finished reading the book and agree with your thinking, but before I call my uncle to help - I wanted to have a good idea of what might be involved. I hope you are still available - looks likes this was from a while ago. I have a Hayward H Propane Pool Heater. Thanks!
Tammy
snipped-for-privacy@gmail.com wrote:

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On 6/26/2011 7:18 PM, tschaefer wrote:

or the heater unit will burn out. To assure adequate pressure, there is a sensor installed in the main gas valve circuit. This is what the OP is jumping out. It is possible that the pressure switch is faulty, the pump is clogged or otherwise obstructed, or the filter is dirty. I would explore the easy stuff first.
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