stejus said:
Now that you say it may be an electrical component (solenoid), it may make sence. We had an electical surge that fried my circulation pump for the forced hot water. The domestic hot water works fine, but the heat triggered by thermostat doesn't because the circ pump was fried. It's a becket burner, about 10 years old. The furnace (boiler) is a Burnham about 20 years. What am I looking for on the burner to point me to the clean cut solenoid?
It would be obvious. There's a 10 - 20 second delay on every cycle where the blower motor is spinning with no combustion and when the valve opens, there's the woosh when the firing starts. On the left side, the label on the pump says "cleancut" and the valve sits right on the top of the pump with a wire to the Fireye controller. The Burnham should be a good boiler, cast iron sectional.
That's my first guess, evacuating the flue gas, purging. If the boiler is firing and the through water temp is too low, < 140 deg, that type boiler is not rated for condensing, low temp operation. Boiler operating temp makes a big difference. Return water temp should be > 140 deg. It looks like it may be a tankless coil for DHW, so shorter, more frequent firing cycles. An indirect tank would give you a longer hotter firing cycle. I don't know what the least expensive fix would be. A good boiler guy should look at it.