Thats the one. The reason i say make it match is because there are many kinds for many applications. Some are only pressure, some are for low pressures, some are for high temps. But most any valve meant for a residential water heater are fine. That DOES NOT INCLUDE the ones for tankless heaters. They are usually pressure only (they dont have the white probe sticking out past the threads). Note that some water heaters have a longer than standard valve because they have thick insulation on the tank. ie: http://t.homedepot.c...N&showPLP=false
Try to avoid the cheap ones. Not worth the time.
Get new valve (same rating on tag)
Turn off power to heater (& gas too if u r the paranoid type)
Drain water out of old t&p by pulling handle till no more comes out (dont let anyone open a faucet while doing this) or at bottom boiler drain
Thread tape new valve (5 wraps should do it)
Remove old valve
Thread in new valve
Water back on
its not so much a crap shoot. the resistance of flame sensor wire can be tested. if the pressure switch is dropping out when the gas valve opens, the pressure switch can be monitored by hooking a volt meter on both pressure switch terminals after the switch initially closes and see if the meter ever reads voltage (open switch) while the gas valve is in play. (set your meter on voltage and to min/max).
problem remains: gas valve not opening on time or not staying open long enough. the only question needing answered is whether or not the problem is the gas valve itself or a component involved in sending voltage to it.
it would still be nice to have the amp draw and coil resistance of the gas valve.
if the gas valve dont stay on more than 2 seconds: it aint the flame sensor. there is not enough to sense. therefore the problem is related to why the gas dont stay on long enough. you have to keep order of operation in mind.
draft is proved. (inducer pressure switch, centrifugal switch, etc)
igniter comes on.
gas valve opens.
flame is proved.
we barely get into flame ignites but we know that the actual ignition is not the problem because it ignites AS SOON AS the valve opens. if there was a noticeable delay in ignition from the time it opened then "flame ignites" would be the problem. so "gas valve opens" is the issue. either it is taking too long to open from when it is supposed to or it is not staying open long enough, check all things needed for gas valve to open on time and remain open with good flow.
how long (and at what point) does valve get 24v. do not go by the click of it opening. go by the volt meter. if it has 24v but takes precious time to open that is bad. the time you get to prove flame starts when voltage is sent to the valve (or supposed to be sent). not when the valve clicks open (the board does not know the point that the valve actually opened). unhook the 2 wires from gas valve. hook to volt meter. time how long igniter is glowing before 24v is on wires. how long does it remain on wires? same with valve hooked up or not? coil resistance? gas valve amp draw?
this is why i asked about a low pressure switch. it is between the board and the gas valve electrically speaking (if you have a low pressure switch)
this a wild shot, BUT... now that you mentioned "LP" again (i missed it in original post somehow), does the gas valve have a low pressure cutout switch? they are sometimes added to the gas valve during conversion to LP. if the pressure drops they cut the voltage to the gas valve. they are generally used to keep the furnace from burning poorly when the owner forgets to fill the tank and pressure drops off. if you have any gas supply pressure issues (tank regulator or house regulator or pipe obstruction, etc) or if the pressure switch is going bad, then this could happen:
the gas valve is closed, the gas pressure is built up in the lines behind the closed gas valve to the normal operating pressure, the pressure switch is closed because of adequate pressure - allowing voltage through to gas valve, board sends voltage, the gas valve opens, the gas starts to flow, the gas flow is low therefore the pressure drops, the pressure switch senses the low pressure and opens, the voltage to the gas valve gets cut out. repeat.
check ohms on gas valve solenoid with wires disconnected (sometimes this is helpful, sometimes not, depending on the valve & type of coil wiring. ie: diode involved or not, etc). you can also check gas valve amp draw & compare to valve rating if provided.
also check for how long the gas valve actually receives 24v. you may have done this. i wasnt sure from ur post.
chances are still pretty high that the board is the problem.
yep, a lot of times they look pretty clean. but the buildup can be like a thin film. it insulates the rod from the flame. the rod is not trying to be heated by the flame (as a thermocouple does) it is conducting electricity through the path of the flame (not exactly, but close enough). if you picture that it is operating this way it is easier to understand that it has to be good clean steel so it can conduct electricity. a good scrub once a year with a scotch brite pad will usually fix it up. if the rod is black and sooty it may indicate poor combustion and the problem would need looked into.
these sensors hardly ever need replaced. if the ceramic insulator is busted or the wire connection area is bad then yes, replace it. but if there is still steel forming the part in the flame, that can be cleaned, then it should be fine.
flame sensor, as said, probably needs cleaned. most of the time it is a single steel rod that sticks into the flame. usually in front the last burner, opposite the ignitor (the part that glows red when lighting). it is likely held in by a 1/4" hex head screw and the sensor has ONE wire hooked to it that goes to the control board directly. (i dont know ur particular furnace specifics off hand.) when the sensor gets too dirty (soots up) it sometimes works and sometimes doesn't.
Nothing is unrepairable, but it depends on skill and reasonable cost. In your situation it sounds like the techs have not had enough skill and have exceeded the cost (time = cost) portioned out by the factory. The nice thing about DIY is that you have much more time available to fart around with the machine (if you have some skill to counterballance). This unit will be one hell of a story to tell if you fix it.
i have had many where the burner was a little dirty (or turned slightly grey) and i increased the reading several microamps by cleaning the area of the burner where the flame comes out from (3m scotchbrite pad). not saying that is absolutely the problem. but something to consider if the grounding of the burner has already been checked. also once in awhile the flame sensor rod gets glazed and touching it a little with small very fine file will help. (don't leave gouges, just very lightly)