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.

wrote in message
oups.com...
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