One zone at a time?

Is there anyway to make one zone at a time go on rather than the whole house which brings the boiler temp down to a point where it doesn't heat effectively? I have the Taco SR506 Zone Switch.

Thanks,

Dave

Why do all the zones call at once?

Rob R. wrote:Why do all the zones call at once?

I've seen mine do it randomly on very rare occasions. Not all zones calling at once as in 100% simultaneous, but close enough for all practical purposes. The independent zones thermostats dictate this.

My cure is that an aquastat shuts down my single circulator (in a 4 zone valve system) whenever the boilers internal temp falls to 145 degrees. This permits the boiler to recover and be strongly on the temperature upswing when it permits the circulator to run again at 155 degrees and once again supply heat to the calling zones.

Since my boiler fires at 170 degrees it is quite rare indeed when it is brought down to 145 degrees, but all 4 zones opening at once after each loop has been off long enough to cool down appreciably can do it.

That's one reason for a bypass valve setup. You can divert a certain percentage of that water back into the system so the boiler isn't shocked. On my system, I use hand valves to slow the flow, since I don't have a bypass loop.

A large radiant zone can do this very easy. When my shop kicks in you can watch the temp fall 20 degrees in 3-4 minutes. I lowered the low limit so the circ runs at a little lower temp and it really helped. 160 down to 150 made a huge difference in recovery time.

When the system is correctly balanced - the zones circulate more than not and this drama is eliminated

Could a "priority" zone control module be utilized to partially accomplish the OP's desire for only one zone to call for heat at a time? My thought would be to place the homes most critical to heat zone loop (or perhaps better, the loop most likely to bring down the boilers temperature the most single handedly) on the "priority" leg of the control module. The effect would be that whenever the priority loop is calling for heat the other loops zone valves or zone circulators would be forced to shut off until the priority loops thermostat is finally satisfied, and only then would the remaining zones get their turn to receive heat. It might be a kludge means to accomplish the goal, but at least it would not require any piping modifications. And if it fails at accomplishing the task, just switch off the control modules internal "priority zone" switch, and everything is back to how it was to begin with.

And besides, what is a priority control module for anyway? The only other (good?) task I can envision off hand is to keep an indirect hot water tank loop hot (while permitting the house itself to cool down) so cold showers don't occur while the boiler is otherwise trying to do something as mundane as keeping the house heated.

I've been watching closely and with the colder weather I'm not seeing my boiler drop below 160 degrees, no mater how many zones are calling for heat, or in what sequence, including all at once. The phenomenon of having multiple simultaneously calling zones bring down the boilers temperature too much seems to be more likely with a "sleepy" boiler in warmer weather conditions than with a repeatedly revved up boiler in cold weather.

Sting, did it just take me about a hundred words to say what you had earlier said quite effectively in only about 15 words?

I have 5 zones, one of which is huge cast iron radiation from the 1890s. For this zone I have a separate zone relay that turns on the boiler immediately when it calls for heat, and I have an aqua stat for it that I keep at a high temperature.

This throttles the zone on and off, to keep the boiler from being dragged down all at once. If you have old cast iron zones they are probably oversized for gradual convection flow, so these controls help to replicate a similar action with modern circulator pumps.

Rob R. wrote:Why do all the zones call at once?

My wife and I both work, and we turn on different zones when we get home. I turn on the "man cave" zone first and kitchen to make dinner. My wife turns on the bedroom to change, and living room where she works on her computer. So there is 4 zones. Of course, the 5th zone always seems to turn on by chance. Given it takes a while to heat up any one zone from a day of being mostly off all zones tend to go on at the same time in the evening and drops the boiler temp down real fast. Once the temp is low it takes a long time to heat the house. I increased the teeth setting to 5 from 4 which seems to have helped. I also increased the low setting to 160 (actual) since the setting temps are off.

Thanks,

Dave

Does the boiler attempt to run up to the high limit during a heat call? Or does it control off the low limit setting?

How about not setting all the zones back (or as far)?