Motorhome is a 1993 Coronado, Furnace is the normal therostat controlled Suburban forced air unit. It was working fine last time I used it. Getting ready for a trip and checking all things out, furnace came on as usual, but did not ever light and blow heat. I am suspicious it is the igniter. Are they difficult to replace? Any help in how to test and replace will be appreciated. Thank you in advance. Mel