I have a tappan gas furnace -model L1ra 090c 16b. Nordyne control board 624631a The problem started with no heat. Status led (red) blinking 4x. The ignitor would glow, but no gas flow. An hvac tech friend came over and we did the following; 1 check all roll out and limit switches with multi meter=all good 2 check voltage at gas valve =24v when ignitor comes on 3 check resistance of valve (across both terminals) = OL/open. Also open from each terminal to the valve body. 4 replace gas valve=ignitor glows, but no 24v to gas valve so no flow. But now I have constant 15v at gas valve 5 checked flame sensor, cleaned with scotch brite= ignitor glows, voltage increases from 15 to 24v and furnace lights and runs as normal shuts down as normal under thermostat control. 6 check and adjust gas valve output with manometer= when t stat shuts furnace down, out put is zero verifying that the valve is indeed closing. This brings me to my main concern- is this constant 15v at the gas valve normal? If not, than most likely the control board has a bad relay and probably killed the original control valve? Thanks for any input.

Greetings all! Woke up this morning to find out that my heating system is not turning on. Sentry s-90 dp gas hot water system, 1 zone. I spent the last few hours reading and researching, putting pieces together but there is still something missing. The problem: When the thermostat calls for heat, the relay clicks but the damper does not move, therefore heat does not go ON. But.... When I drain some hot water and the boiler gets filled with fresh cold water and the boiler water temp drops below the specified 180 degrees, the damper opens, and heat goes ON until the 180 is reached. This leads me to believe that the rollout switch and the blocked vent safety switch are OK since they allow the the system to turn ON. This also leads me to believe the damper is OK because it does open and close when the system calls for internal water temp of 180. Here is what my plan is for tomorrow anyway: 1. Verify the rollout switch was not tripped with a multimeter. Just to be safe, try to jump it, see if that helps. 2. Verify the blocked vent switch was not tripped, try to reset it, make sure it is not an open circuit, try to jump it. 3. Verify 24VAC across relay B1 and B2. Now.... What additional steps are involved in the sequence when the thermostat calls for heat vs. when the furnace itself calls for heat (to keep water temp at 180)??? Does this point to the relay being the faulty part? Also...is the damper really necessary? Is it simply for efficiency? I'm thinking if I can't resolve the problem right away, maybe I can remove the flap from the inside so that it is always open and jump the damper switch so that it thinks its open, in turn letting the gas valve go on. Thoughts? Thank you