View Full Version : Simple control question?
12-09-2006, 12:20 PM
I have an older boiler with a high limit control and a low limit aquastat. I want to configure it so I can set the low limit at 110 degrees and when heat is called for the water will will heat up to 160 degrees until the load is satisfied and then go back to the low limit temperature. The high limit is set for 170 degrees.Is there a contoler that will allow me to do this?
12-09-2006, 04:07 PM
You have a room thermostat? What does it do?
12-09-2006, 06:13 PM
I have two zones, each with a thermostat. What I was hoping to do was have one control on the the boiler so it doesn't matter which zone calls for heat, the burner comes on and heats the boiler from the low set of 110 to 160 while there is demand for heat, and then it goes back to the low set temperature of 110 once the demand is met.
Old boiler you said? If so how old and what kind? I would plan on replacing boiler soon your going to kill it. Why do you want to do this? How big are the zones? is there pumps for each zone? What are the zones AHU's or baseboard?I would install teckmar (water reset control)if no call keep boiler off when there is a call have Boiler start and have low limit set no lower 140 (130 is pushing it if it cast) set up reset curve and let it run.
12-09-2006, 09:44 PM
Any decent boiler tech should be able to get and install a 'triple aquastat control' for you. From how I read your original question that is what you need, one temperature for domestic water heating only, a second higher temperature for zone heating and a high limit.
12-10-2006, 12:58 PM
Thanks for your input. If I kill the boiler so be it, but it seems to me that the usual answer is that it needs to be replaced. I don't buy it. The boiler is a converted coal burner made by National Premier Boiler of Johnstown PA.with a 195,000 BTU output. A bit large for todays standards. It feeds two large zones about 1300 sq ft each, one has radiators and the other was converted to base board. Presently the DHW coil only providers preheated input to an electric DHW. It works well and is basically backup to the woodstove except in the real cold spells here in Maine. It is a high volume boiler so that is why I want the low limit so low, in the summer I run it at about 100, with no problems. But it is a pain on the cold days to have to reset the limit to 150 to get some heat to catch up. The problem is that what I want to do is a bit unconventional and my local guy just wants me to get a new boiler. That makes no sense as I am using only $1000 or less a year now for oil, it works fine with a modern flame retention burner, and a new boiler might save me $200-$300 a year so the payback would be measured in multiple decades. Probably longer than the life of a new boiler. So it makes sense to experiment with what I have and maybe have a paid for system that is old but with modern controls efficient. An indirect boiler fired DHW is next once I see how the preheated electric is working.
12-10-2006, 02:11 PM
You need two 24V relays with normally open contacts wired in parallel with the low limit aquastat. The coil sides of the relays should be wired to the existing zone valve or circulator pump relay for the two zones. That's assuming there are no existing dry contacts on existing relays.
was this an old gravity system at on time? sounds like it but I could be wrong. Use an aquastat for low limit like you said use endswitches or relays off zone valves that would send power to a simple reset control (taking power away from low limit). The reset control sensor (water sensor) can be strapped on to main header with out cutting into boiler (insulated well) put outdoor sensor on south facing wall and set it up. You now will have the best of both worlds that you are looking for. On a 50 deg day you can have 130 deg water (if you want) and on a 0 deg day you can have 150 deg or what ever you want. You might make enough saving to save for a new boiler after the acid eats away boiler (just my thoughts) good luck
12-17-2006, 12:45 AM
tripe aquastat will do it, should run it higher though and get a mixing valve for the dhw loop.Running the boiler at 110 will produce an acidic condensate and eat at the boiler. Over time it will cost you a boiler.
12-17-2006, 10:17 AM
Cold start the boiler and install a boiler bypass. The boiler heats up faster and heats less system water. This avoids thermal shock and flue gas condensation.
Do away with one aquastat wire T-T through the other aquastat and your circulator control. End switches activate circulator relay. One set of contacts starts circulator and second set of contacts makes circuit for T-T. Both using normally open contacts.
03-26-2010, 06:36 PM
I have a problem with my John Wood 30 gal oil water heater.
I get 146 degree water even when the aquastat is set at 100 degrees.
I replaced the aquastat still same problem. I also took out the well to check for any build up - none. Could it be my burner control box ?
Honeywell R8184 G 1427 ?
03-26-2010, 07:40 PM
Where is the aquastat installed in the tanK? If you turn down the setting does the burner go off? Is there another limit in the tank that is controlling the burner?
03-27-2010, 03:54 PM
do your gas bill a favor and get a small condensing boiler installed by a pro
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