Dave in Mass
New Member
My boiler is a Dunkirk, about 5 years old, with Taco PC700-2 control using outdoor reset. The house, near Boston, has cast iron radiators and cast iron baseboard, and is comfortable. The boiler also has a zone for indirect water heater. The problem is that in very cold weather, recently as low as zero, with a boiler design temp setting of 160 and an outdoor design minimum set at 15 degrees, the boiler heats up to just above 170, pressure rises to 35psi or slightly more, and it will discharge water thru the pressure relief valve every heat cycle. It continues to do this, but less, now that outdoor temp is about 40. My uninformed suspicion is that the outdoor reset is correctly allowing the boiler to exceed 160 to compensate for low outdoor temp. To avoid triggering the pressure relief valve should I change the setting for outdoor design temp, perhaps to zero or 5 degrees? I hate to do it for the few days needed in most years.
Is it reasonable to introduce a switch that would turn off the outdoor reset thermistor and defeat the reset feature?
Could the pressure causing water discharge be eliminated with a larger Extrol tank? It is size 30 now, and because of space concerns it can't be exchanged for a larger one. I would have to tap a second tank into the piping elsewhere. Would it cause any problem doing that? All wisdom and insight gratefully received
Is it reasonable to introduce a switch that would turn off the outdoor reset thermistor and defeat the reset feature?
Could the pressure causing water discharge be eliminated with a larger Extrol tank? It is size 30 now, and because of space concerns it can't be exchanged for a larger one. I would have to tap a second tank into the piping elsewhere. Would it cause any problem doing that? All wisdom and insight gratefully received