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Posted by HeatPro on January 24, 2010 at 11:06:30:
In Reply to: Teledyne Laars MiniTherm JVT-75C conversion to electronic Pilot. posted by Trish on January 24, 2010 at 10:56:04:
Have replaced the thermal coupler, adjusted the thermostat, etc
+++ Not enough work to keep it going. Just having the wrong size and shape of flame is enough to stop a thermocouple from working, no matter if new or old. The problem would be fixed in ten minutes by an experienced gas repairman.
well it may or may not be the thermocouple below is just some of what it could be.
1)Pilot flame
first you need to check that the pilot is on(lit)has it a correct size and flame pattern and is playing the thermocouple in the right place there is a hot and a cold spot on a thermocouple and it will not work if the cold spot is heated or the hot spot cold
2)Thermocouple may not be given right voltage
3)magnetic valve faulty
4)contacts could be dirty stoping voltage
5)interlock like The E.C.O. may have failed or operated
6)pilot flame may blow out from the main burner lighting or turning off (pilot in wrong place)
... and so on and on
a. low gas pressure
b. moisture dripping on pilot
c. dirty pilot orifice
d. dirt in pilot tube
e. low pilot adjustment
f. high pilot flame burning thermocouple out
g. heat exchanger hole so blower blows flame out
h. bad contact of thermocouple to gas valve.
i. overtightening of thermocouple end to gas valve so connection poor by crushing connector.
There are two tests to be made. The thermocouple must be tested to assure that when the pilot flame is applied, the thermocouple creates the required millivolts to hold the pilot gas open. This requires a millivolt tester while the flame is applied. There are tools available to do this test from Honeywell at the local supplier.
Once the thermocouple is tested and found to be OK. then the thermocouple is applied to the gas valve. The connection at the gas valve can be tested for continuity to see if it is broken or not using an ohmmeter. If there is continuity, the gas valve should hold open from the thermocouple current.
I would be surprised if thermocouples and gas valves would have problems from the factory. Most suppliers will not accept electrical control parts back, as it is the contractor's responsibility to test that they are receiving good parts. A supplier can not run a business with the expectation that electrical parts will be used as test devices by inexperienced novices until they are successful at performing the most basic of technical repairs.
GET A SECOND LICENCED GASMAN TO CHECK IT OUT
If he doesn't have his volt meter and his gas pressure meter in hand
as part of his kit hes not the one you want
"Buyer beware" and "You get what you pay for" apply here