SF-260 Issues

Hi, I'm new to NEPA and new to boilers. I purchased a house with an existing Oil/Coal parallel system using a SF-260. See the OLD Boiler PDF for the design. We spoke with the previous owner to learn the basics and fired the coil boiler up last week. We noticed that during a call for heat it would fire the oil boiler almost immediately even though coal boiler had 190 deg water available. In researching the issue, I found this very informative site ( thanks BTW for all the info). I discovered my SF-260's s350 controller was connected to the Grundfos between the boilers as the dump control. I learned here that the circulator pump between the boilers should run 24/7 or be wired to come on above 140 deg. I chose to connect it to run 24/7 during heating season. I also changed my dunp zone to use a dedicated taco 007 that I placed in-line with my original main circulator. See NEW Boiler PDF for design.

When testing the new design last night, the heat started to work perfectly. Upon a call for heat, the oil burner did not fire and the system used the water from the coal boiler. But... After a while I discovered the circulator between the boilers was pushing heat up into the house radiators by itself even when there was not a call for heat. It began to run constantly at about 150 deg. The house warmed up nicely, but... the boiler pump continued sending everything up to the house radiators.

So, I briefly tried to wire the boiler circulator pump to run only on a call for heat along with the main circulator. See Boiler 3 PDF. This design worked perfectly during 3 or 4 calls for heat and I almost thought I had succeeded in finding the perfect solution for my system when I noticed the coil boiler activate the new dump pump and not lose any heat. It continued to climb. If the boiler circ. was not running, no water would be pulled from the coal side. I rewired the grundfos to act as the dump zone again and began making drawings to post here..

I think I've caught the obsession as I've ordered the books and plan to "fix" and "tune" my system.

Any ideas on what may be needed? Maybe check valves somewhere to prevent the boiler circ from pushing up to the radiators???

Thanks in advance for you great ideas.

If I understand correctly, I think you have it correct right now. On your last drawing, the dump should be connected to the Grundfos as well as the Taco you added. All other connections would stay the same. Or you could eliminate the second Yaco by connecting the dump zone to the Grundfos and the original Taco. If I knew how to modify your drawing I could make it more clear. I am not as knowledgable as others here, but I think that would work.

thanks. I think that would fix the dump zone, but what about calls for heat. The main circulator does not pull any water from the coal side unless the boiler circulator is running. I now have it connected like the original design (old pdf) in order to provide a safe dump. The calls for heat worked perfectly in the boiler 3 configuration but the dump from the added taco would not pull water so the temp kept rising even though the new dump pump was running.

Maybe I can do a better job making it clear (I'm not always good at explaining things). In your "last design" diagram, you show the L8124A connected to the Taco and the Grundfos. The S350 dump should also be connected to the Taco and the Grundfos (you could remove the second Taco that was added). When connected this way, both the Taco and Grundfos will run on a call for heat, and/or on a call for "dump".

OK, I've been thinking about that too... It will take some interesting wiring to include 24v transformers and new relays to make it work safely but it may be the best way. I had hoped to figure out a more standard solution that included running the boiler circulator 24/7 (or above 140 deg) so I didn't need to tie the grundfos into the main circulators or dump pump.

question do you need both boilers to heat with???? when I bought the house I had the vanwert stoker in here added a gas boiler next to it and have it set up so I can run one or the other if the stoker is running the gas boiler is shut down ( by the way that 95 % of the time only use it spring and fall ) I don't under stand why you need both running at the same time ????

DHW is from oil boiler. I also would like the oil to be a auto backup for the coal HEAT.

DHNEPA wrote:DHW is from oil boiler. I also would like the oil to be a auto backup for the coal HEAT.

is the DWH a coil in the oil boiler or is a zone from the boiler

jeff

DHW comes right out of the oil boiler

I may have found the problem to my loop circulator heating the house... The flo control valve at the supply to the radiators may be faulty. After reading up on the flo control valves I checked mine and discovered it was backed out about 1 1/2 turns. I shut the flo control valve by turning it clockwise until tight and turned on my loop circulator. No heat was felt above the flo control valve. So far so good... Then I forced a call for heat to turn on the main circulator. Still no heat above the flo control valve. I manually raised the flo valve and immediately got heat into the house.

Am I on the right track? Isn't the flo control valve supposed to be turned clockwise until it stops? This newbie to boilers is looking for confirmation.