When I arrived at unit, I was told heating didn’t operate. I ran thermostat in heating mode and went out to furnace. You could hear system wanting to start and smart valve clicking in and out. Smart valve was getting power, also the spark igniter. There is a motherboard in spark igniter box. Every time I kept tapping it, it would open and start burners for one second. Spark igniter is failing and part can’t be found in any distributions. System is thirty plus years. Owner is having construction done to home, and will notify us about potential replacement when ready. Model and serial to the furnace is not readable. Charging for diagnostic only today.