Hi everyone! I have a oile-fired boiler which serves two air handlers and the water tank. Once in a while (seems like every night after I lay down!), the upstairs (attic) air handler gets the signal from the t-stat to start blowing air. Instead of relaying to the boiler that the boiler should start warming up the water in the hot water loop, the AHU just blows cold air. Then I need to go downstairs and tuen up the first floor T-Stat. The AHU serving the first floor calls for hot water and eventually the loop going upstairs heats up. What do you think the problem could be? First I thought it was an air pocket or a pressure problem, but pressure on the upstairs loop looks okay, 20-25 psi. Please help!