On 2019-03-19 11:17, wrote:
A couple of months ago when it was coldest my central heating stopped
igniting. My impression from the sounds it was making was that the
thermocouple was bad or the pilot light that would be ignited was
dirty or some such so that the flame wasn't close enough to the
thermocouple of inform it that there was a real flame there and turn
the full flame on.

The repairman came out and said that the pilot and thermocouple was
OK and changed out the main gas valve. The heater appeared to work
for six weeks and then as the weather got cold again started not
lighting again.

The company sent another repairman out and he said that it was the
main control board and replaced that.

I am now $1,600 into "repairs" and sure enough - the heater isn't
lighting still.

It would appear to me at this time that there is nothing more to
replace but the pilot tube and the thermocouple. So I wonder how to
convince the repairman that there is something wrong with one of
those?


We had that happen a long time ago and the cause was the electronic
controller board. The central propane furnace would go VROOOOP ..
PHUTAH-PHUT ... RUMBLE ... VROOOOOOOOOP ... and never stayed on anymore.

When the technician came out he exclaimed "Oh look, an old Fenwal
controller board!", saying he was amazed that it lasted this long. He
switched it out against one from another manufacturer and all was well.

I asked him to leave the old board and when probing it I found that the
triac that controls the main burner valve had gone partially bad so it
wouldn't be able to send a full current through the valve solenoid
anymore. Could have kicked myself because instead of paying a few
hundred Dollars I could have gotten one of those triac for a couple of
Dollars and replaced it. If these triac are on a separate driver board
then check that.

There is also a suction sensor, for example a flap in the intake stream
that operates a signaling switch. If that got crudded up it might at
times falsely signal a failing air draft and that would cut the main valve.

--
Regards, Joerg

http://www.analogconsultants.com/