I attended Heather and andrews home in cochrane to perform a tune on their furnace. I found that the furnace is in good operating condition. However, the cuts are dirty, burners are dirty, main blower is dirty and the ac coil is plugged. This all contributes to the hig temp rise which can damage the heat exchanger. I also found that the fan reostat on the fireplace s faulty. Andrew is going to discuss the options with Heather and get back to us.