Burner and pilot won't stay lit!

[tomfish726]

I'm looking for some help with an old boiler. I have a Hydrotherm HC-85 boiler with a NEW Taco circulator, a NEW Honeywell VS820 gas valve with a NEW 750 millivolt generator and a NEW thermostat.

The problem I'm having is keeping the burner lit. The pilot lights fine and stays lit, when the thermostat calls for heat the burner lights and will burn for a few minutes or to full boiler temp but somewhere in between both the burner and the pilot go out. The pump will continue to run.

Anyone run into a problem like this?

Any help would be greatly appreciated.

THANKS!

Tom

[HayZee518]

sounds to me that the millivolt generator, the flame senser is not in line with the burner. while it may be inline with the pilot, when the main gas opens it robs the flame path from the millivolt generator. the millivolt generator - the thermocouple provides a 750mv signal to a very small electromagnet within the main valve for the pilot. once the voltage is not at the pilot valve its valve will close, but because there is still pressure behind the main flame the main flame continues to ignite. once your temp is reached the main valve closes, flame goes out, but the pilot is also out. so you have to relight the pilot until the thermocouple heats up enough to pull in the pilot valve electromagnet again. then the cycle repeats itself. try moving the thermocouple more into the main flame as well as in the pilot flame.