I have a ducane cmpe100u4b furnace. The thermostat triggers the furnace to turn on but all I hear from the furnace is a low hum for about 1 minute then it shuts off. LED light is blinking non stop. I activated the reset switch inside the door panel and replaced the door...still nothing. Shut the circuit off and back on same issue. All inside vent and returns are free from debris. Outside vents are clear of snow. Unit was installed in 2008. I've only owned the home for 2 months. Doesn't look like any cleanings have been done by previous owners. Not sure what the constant flashing means as it isn't one of the options listed in the manual. Suggestions please?

my shop furnace a hot surface ignition Modine 'hot dawg' (HD 75AH0134) wont seem to ignite. Here is the back story and what i've done so far. found it with on with the main blower motor running, unplugged it and plugged it back in only to have it not ignite (physically watching the ignitor not light up), replaced ingitor and it lit up and lit off the furnace one time only to go back out and not repeat. i left the furnace unplugged for several days and when i plugged it back in the same thing occurred with one light off and not being repeatable, i then set about troubleshooting the components which in retrospect seems unnecessary now as i know that most of them with give a LED fault code and i saw none at the time. pressure switch ohms out good both on bench and switches fine while hooked up, high limit and flame rollout limit switches are all made and in the satisfactory state, jumpered out the thermostat with no difference, checked both sides of the transformer and i have a good 120VAC and about 27-29VAC on the control side, i got sidetracked and was thinking maybe it was the fan relay and control board so i changed that out as well with no difference. Now i cant get it to light off at all and when i unclip the wiring harness to the ignitor and read voltage across the output of the fuel valve on startup i got from nothing to only about 1vac when it should be (as i read the schematic anyways) 120vac, this 1vac holds for what seems to be a reasonable amount of time to lit off the gas but surely thats supposed to be 120vac or at least 24vac ? i am planning on buying a new gas valve (Honeywell SV9410 or Modine P/N#5H76382) on monday when my local shop opens but they're VERY expensive (mainly cause its made by Moneywell) so i'd really like some other tricks to try before plunking down ~$350 on a valve. but it does seem to me that if all the start permissive's are good then only the gas control valve can be responsible for the output to the ignitor???? and for bonus points if anybody as ever taken a gas valve out of a modin hot dawg i'd like to hear how you go about that because it sure doesn't look like there is enough room to rotate the valve ???? Thanks in advance for your brain power!