AQUASTAT PROBLEM WOOD BOILER

[Brimfield]

I installed a Central Boiler furnace to heat with my propane boiler this year. My initial problem was I plumbed it in direct so the pump from the outdoor boiler was directly plumbed in with the house system. The problem was once the outdoor furnace shut off the system would siphon off. This was due to the wood boiler being downhill and once the circulator shut down the water drained from my radiators to the boiler. So the fix was to put in a heat exchanger , one side to the outdoor furnace and the other to my indoor boiler this allows me to have the house side with 5 psi pressure and the furnace side open loop. The problem is my indoor boiler has an Aqua stat with a low of 140* that kicks the boiler on when any of my three zones call for heat. The outdoor furnace is running at 185*. The problem is until the indoor boiler circulates enough to pick up heat from the heat exchanger the propane fires up. Can I change the aqua stat on the indoor boiler or loop it in with the outdoor furnace somehow?

 

[Raspy]

How about if you put another aquastat on the outdoor boiler that turns on the outdoor pump when that boiler is up to temp. The power to that aquastat can come from the indoor boiler and is energized when you call for heat. The outdoor pump will only run during a call for heat. This new aquastat can also be a dt/dp unit that cuts power the the indoor burner when the outdoor pump is running.

So, if I understand the setup, the outdoor boiler comes up to temp, there is a call for heat and the outdoor pump gets energized from the indoor boiler power through the new aquastat switch. When the new aquastat switches, the extra contacts disable the burner on the indoor burner.

If the outdoor boiler is cold when there is a call for heat, the indoor boiler works normally and the outdoor boiler is out of the loop.

 

[aczlan]

I also have a combined system, but mine is all pressurised and all indoors.
What mine does it when the wood boiler is up to temp, the wood circ pump turns on and circulates water through the oil boiler.
The oil aquastat came with two sets of contacts, so it runs the circ pump when heat is called for, but it only runs the oil if the temprature setpoint.

Aaron Z

 

[Winmac]

I don't know if you have a aquastat problem, maybe more of a system design issue.

Burning wood outside is convenient but getting the heat in the house where it's needed can be complicated.

Dose the burner only cut in when the system is coming up to temp or is it all the time when calling for heat?
Dose the indoor boiler have two circulator pumps? A typical heat exchanger system will.

 

[nybirdman]

The way my son's is set-up(Central Boiler) the wood boiler pump runs constantly and the house circulators come with demand. Indoor aquastat is set at 135 and never comes on.He is not using a heat exchanger,the out-side boiler is piped direct to the inside boiler and maintains it at 185.
The only change we had to make in the house was put the circulators on the supply not the return.

 

[Brimfield]

I should have explained the set up better than I did, I do apologize. The Central Boiler outdoor furnace has its own circuit board. It measures the water temp circulating coming back in and fires the heat according to its set point and demand. It has a circulator that is plugged in and runs as long as it is plugged in. This goes into a heat exchanger and back to the furnace. The indoor boiler has an in and out from the heat exchanger that separates the two sides and allows the indoor boiler to run at 5 psi pressure to feed the three zones, two are heat for the house and one for hot water that is heated indirectly from the boiler. The indoor boiler has the only aqua stat in the whole system. When heat is called for in any of the three zones the aqua stat measures the temp returning back to the boiler and will fire the gas boiler if that temp is below the low Point. So if no heat or how water has been on the system gets a shot of cool water and makes the gas come on. If I wire an aqua stat to the incoming hot water from the outdoor furnace in series with the boiler will this stop the boiler from coming on when the return to the boiler is cold?

 

[Raspy]

Brimfield,

Did you not like my earlier idea? I can't understand your series idea without more detail.

 

[nybirdman]

Yes,put an aqua stat on the supply from the outside boiler;that should do it. If your outside goes down for some reason your inside should pick up the load.I would set it 15-20 degrees below the outside boiler.

 

[Winmac]

Before you commit to making the changes I'd suggest temporarily disconnecting the burner so it will not fire, and watch he the indoor boiler temps as it operates to see if it maintain sufficient heat.

 

[MNBobcat]

Don't put an aquastat on the outside boiler. That circulator pump should run all the time. It helps prevent your outdoor boiler from getting too hot and boiling over. Also I think it keeps a more constant water temp in the lines.

Go Here and click on the System and Wiring tab and see what they recommend for your type of installation.