I've been reading on some past threads that some people either just shut down power to their boiler or run a timer that shuts down power to the boiler after X # hrs. This is to keep water from continuously circulating until the temp at the boiler is below the pump launch (less hysteresis). I was looking into doing this with a timer myself for now, but how does this relate to the overheat loop that opens on loss of power? Obviously I would wire so that the overheat loop doesn't open when the timer is done, but I guess my question is that If the timer goes goofy and shuts the boiler down halfway through a burn, and the overheat loop doesn't open because technically power wasn't lost.. is this a concern?
Question on shutting off boiler when storage temp reached
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hiker88
Burning Hunk
Don't you have a close on rise aquastat on the boiler that opens the zone valve on your largest heat loop in case of over temp?
maple1
Minister of Fire
An overheat loop is best set up so that it will open & dump heat either when the boiler gets too hot, or there is a power loss.
To do that, you would use a break on rise aquastat or controller, and a normally open zone valve in the dump circuit. Then the zone valve is kept closed by the application of constant power to it through the aquastat - until either the stat sees a temp that is too high & then breaks the circuit (which would also preferrably then start your circ pump via the end switch in the zone valve), or the power goes out. Which of course also breaks the circuit (flow would need to occur by convection in that case).
Also I think the typical use of the timer was to shut down the boiler after it burned out & cooled off, rather than when storage got too hot - for those boilers that didn't already have the capability to do so. I think.
To do that, you would use a break on rise aquastat or controller, and a normally open zone valve in the dump circuit. Then the zone valve is kept closed by the application of constant power to it through the aquastat - until either the stat sees a temp that is too high & then breaks the circuit (which would also preferrably then start your circ pump via the end switch in the zone valve), or the power goes out. Which of course also breaks the circuit (flow would need to occur by convection in that case).
Also I think the typical use of the timer was to shut down the boiler after it burned out & cooled off, rather than when storage got too hot - for those boilers that didn't already have the capability to do so. I think.
You would have two aquastats and two setpoints, an operating aquastat and a high limit. The operating aquastat ~ 155 F launches the boiler circ. The high limit aquastat controls the overheat loop. If the system uses a timer, the timer would have to be according to the manufacturer's specifications, as part of the burner fan control. You would not add your own timer near the boiler burner controls, you would use the factory controls.
It's not clear if you want to do heat scavenging or control the boiler circ with a different parameter. I'm guessing in the off cycle when the system has been producing at 180 F and the boiler cools to 160 F, you want to shut off the boiler circ. I have looked at this and have my boiler launch circ set ~ 70 C, 158 F, which is coordinated with the loading unit opening and closing ~ 155 F. As the boiler return protection valve closes ~ 155 F it takes the boiler out of the system except for the boiler bypass pump. The boiler water is mostly circulating just around the boiler, not out to the loads. I have my launch circ temp set just above where the loading unit valve opens and closes, which minimizes the pump running in bypass when the boiler is off.
Right now heat scavenging with the slabs and DHW, the slabs rob the DHW of a little heat. I'm working on a smart relay that will prioitize the DHW for heat scavenging when the boiler is off. It needs a few more input parameters, supply header and DHW return water temp setpoint controls.
When you start talking about the boiler emergency overheat controls, you want to follow the factory specifications.
It's not clear if you want to do heat scavenging or control the boiler circ with a different parameter. I'm guessing in the off cycle when the system has been producing at 180 F and the boiler cools to 160 F, you want to shut off the boiler circ. I have looked at this and have my boiler launch circ set ~ 70 C, 158 F, which is coordinated with the loading unit opening and closing ~ 155 F. As the boiler return protection valve closes ~ 155 F it takes the boiler out of the system except for the boiler bypass pump. The boiler water is mostly circulating just around the boiler, not out to the loads. I have my launch circ temp set just above where the loading unit valve opens and closes, which minimizes the pump running in bypass when the boiler is off.
Right now heat scavenging with the slabs and DHW, the slabs rob the DHW of a little heat. I'm working on a smart relay that will prioitize the DHW for heat scavenging when the boiler is off. It needs a few more input parameters, supply header and DHW return water temp setpoint controls.
When you start talking about the boiler emergency overheat controls, you want to follow the factory specifications.
Wow... semantics make me feel like an idiot. I read the instructions originally as on loss of electric OR a high temp aquastat. Aquastat it is.
A handful of us around here are using cheapo timers to control our fans but not necessarily shut down power to the boiler/circ. I personally do it to prevent the fan from runnung all night while I sleep. I shut off the circ in the morning when I go to work manually.
I also use my timer occasionally to keep a bed of coals in the boiler if I want to start the fire the lazy mans way the following day. This is less frequent, usually only during those times when our temp's stick below zero for a few days at a stretch.
I also use my timer occasionally to keep a bed of coals in the boiler if I want to start the fire the lazy mans way the following day. This is less frequent, usually only during those times when our temp's stick below zero for a few days at a stretch.
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