Wood/Oil Combo Heating Issue

MacPheaa84

I just purchased a home with a combination wood/oil boiler for hot water heat. I have noticed when I start a fire the boiler temperature goes up very quickly and will reach 240F. However when I go upstairs and turn the heat up it will kick the oil burner on, even with the temperature at 240F. As the water leaves, the temp goes down, but the oil continues to burn despite the wood fire raging. The wood is VERY dry and has been in the home for awhile. Also, when I have a fire on the damper of the wood furnace will stay closed and not open up to draw more heat and the oil burner will kick in again. Kind of frustrating as I would like to mainly burn wood. Any suggestions/tips would be helpful.

STEVEusaPA

Brand name/model number? What kind of controls are on it and how are they set?

MacPheaa84

Hi Steve. This is a Benjamin Model CC500. As for the controls and settings - I am not entirely sure as I have limited experience. There are two domestic coils on the back which I am not worried about. And there are what appears to be 3 zone valves. Attached a photo of the temperature gauge which shows around 215F. I took a video but can't share it. The fire is on here, but the oil has also kicked in and I can't figure out why.

leonz

Hello and good morning MAcpheaa84,

Are you located in Canada? If you don't mind questions from a former wood and coal boiler owner;

Your oil burner should "only" activate when the thermocouple senses a low limit temperature in the water.

If the fire burns down and the thermocouple senses a 140 degree water temperature it will start the oil burner.

The water in your boiler should never reach 240 degrees, if it had your boiler would have flashed to steam and your relief valve would have released and blown steam into the basement.

If your oil burner is acting like this you need to have your boiler cleaned, the chimney and flue pipes swept, and the oil burner cleaned and tested for efficiency as your burner is running when it should not be running.

Your combination metric pressure and altitude gauge (triple gauge) is defective and should be replaced.

I have a DWYER 4 inch square triple gauge with a bottom thread on my coal stoker boiler and I can recommend them very highly.

If you have wood fly ash entering the oil burner tube you will have problems.

Please tell us what brand of wood/oil boiler you have and which model it is.

You need to schedule a boiler cleaning before we get any further along in the winter season as soon as possible and purchase a new triple guage.

MacPheaa84

Thank you. I am located in Canada. And this is a Benjamin model CC500

EdTheHeaterMan

A quick look at the wiring diagram indicates that there is no control that disables the oil burner if the water in the boiler is above a certain temperature (like 150° for example) form a wood fire. This seems strange to me but the wiring logic does not lie. The diagram also indicated that you may have a Riello oil burner, Beckett oil burner or an Aero oil burner. Can you tell me what type oil burner you actually have? I can design a simple fix to make the oil burner stay off when the wood fire makes the boiler water temperature stay above a selected temperature like 150° or 160°

If the boiler water temperature drops below that selected set point, then the oil burner will automatically take over heating the home.

EdTheHeaterMan

There is another set of controls that indicate there should be a "Dump Zone" which is a place to send the heated water if the wood fire makes the water too hot. Can you tell if you have such a thing? It would probably be a storage tank of some type placed near the boiler with a separate "Secondary" circulator pump.

EdTheHeaterMan

I think that you are supposed to set the oil burner High Limit to a lower temperature when you are using wood.

Also if the water temperature gets too high from the wood fire, the Dump Zone Valve opens and sends the excess heated water to the radiators to "overheat" the house. That will cause the thermostat to satisfy and cause the wood fire damper to close, thus reduce the size of the wood flame. Looks a little better thought out that I saw at first glance.

So the question now is "What is the High Limit set to on the oil burner aquastat relay?" Try setting it to 160°

Important:

If you are not using the DHW Coil(s) for hot water then you want to set the LOW LIM to the lowest setting available (110° I think)

MacPheaa84

Ed, thanks so much for the info. I am going to review when I get home tonight. There is definitely a dump zone where the excess heat gets dumped to. But even when the dampers close, the temp remains quite high (200+). I will review the settings this evening and see where they are set

MacPheaa84

Hi Ed
This is a Riello oil burner. There are two aquastats on this. One is the wood aqua stat on the top of the unit which was set to 180 lo 200 hi. The oil aquastat on the side was set to 160 low 180 hi. With that said I have not yet made an adjustment since it was suggested my thermostat may be showing incorrect temperatures. As noted previously, when I start a wood fire it really drives the temperature high - up to 240, even with heat being dumped into the dump zone. And when it dumps, the house does get close to uncomfortably warm. I will get someone to check the thermostat on the unit to ensure it is working correctly.