What's the worst that can happen?

J B

No, I have outside control with my Viessmann. And my contractor put a strap on aquastate on the return side of the OWB loop (coming out od the HX) it looks to me like that stat just goes to the circulator pump for the inside loop. Curiously, though it is set at 140 deg, I have never had the pump shut off even though I have let the fire go a couple of times.

J B

Who knows why, but suddenly my Viessmann has decided to rely entirely on my OWB, and now never fires. Yes, that's what I wanted. . .I thought. At what temperature (as indicated on the Vitotronic) will I cause problems/damage to the Viessmann?

Jim

ALH_4

damage

What kind of Viessmann, and why would it damage the Viessmann boiler? I assume the V never runs because you keep the OWB going?

J B

Vitola 200 Oil, with 20 plate HX from OWB. The Viessman used to run to easily - in my opinion - when the temp dropped, depending on the outside temp. Suddenly, the Viessmann NEVER comes on! It was 17 deg this am, and once the inside boiler got down to 118 (multiple zones at once, OWB/HX seems to get overwhelmed at first).

I guess since my contractor never explained anything about the Viessman (this is the first radiant/mod-con system I have ever ownes) I am a little in the dark about what the two different heating circuits are for and whether that low of a temperature will be bad for the V.

Jim

ALH_4

wood & oil

The Vitola should not be allowed to fire unless the wood boiler is not firing or circulating. Obviously, you do not want to heat the wood boiler with the Vitola. Cool water temperatures are not an issue unless the boiler is 180°F and cold water is returned to the hot boiler. The Vitola is even less susceptible to low temperatures than most cast iron boilers.

There are so many different methods for integrating alternative energy sources into a hot water heating system that it is difficult to know exactly how your contractor did it.

If the wood boiler is cold, does the Vitola fire up?

J B

Right now, I don't know. It used to take over quite easily. In fact, to heat the DHW, this HO has been:

1)Putting both heating circuits on standby until the Viessman got to 171 deg
2)Checking the existing DHW temp and setting the desired DHW point at 5 degrees higher
3)When the boiler reached 171 deg turning both circuits back to DHW only
4)Pressing 'party mode' twice to force DHW heating

Yes, I really would go through all that to keep from paying the oilman!!

I had found that a gain of 5 degrees in DHW took 10 degees from the boiler, and anything less than 160 deg in the boiler would cause the burner to start.

Which brings me to the past 24 hours. I noticed yesterday that while the Viessman temp dropped into the 118 range, the burner was not firing. So this AM, I did the usual DHW heating trick as outlined above, but this time put the desired set point up to 140 degrees. It took quite a while - and the boiler dropped way below 160 deg - but it heated the DHW to 145 without firing. This makes me think that something happened to suddenly make the burner NEVER fire.

Which might not be a problem with spring coming, as long as:

1)I am sure I am not going to cause thermal shock and/or condensation where it shouldn't be, and
2)that I do a great job maintaining the fire on nights like tomorrow, when it is supposed to get down to 6 deg!!

Jim

Paul Pollets

Vitola is not a mod-com

The Vitola boiler is not a mod-con. Presumably, you're using the Viessmann chassis burner. Presumably, you're using the Vitotronic 200 control.

The Vitola can handle low water temps, but does not condense by design. Attaching a FPHX usually requires the FT module or Switching Module V. These controls bring the boiler to fire on demand for heat. All is dependent upon the control strategy. Your installer should have provided manuals and instructions on how it operates. How come??

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J B

Lol, I have the manuals, but I'm an HO . . . hell, I don't even know what mod/con means (yes, I know what it stands for) so the manuals are not really for me, plus . . . Viessmann never envisioned adding on an OWB open system with HX to their setup. Now, if solar was an option, I see they have something for that . . .

But you speak of controls. . . there are controls that would make this work more like I want it/it should?? Ok, so maybe as a HO, the way I want it to work is not the way it really should - but any info would be graciously digested!

Jim

ALH_4

piping

The methods shown for integrating solar energy into a heating system are very analogous to wood boilers. The piping is nearly identical, except some OWB's have built in water volume where solar panels do not.

To automatically control a system with an alternative energy source, you need to sense the temperature of the wood boiler and determine if it is hot enough to provide heat to your home. I am not sure why, but I suspect you are not running on outdoor reset? If you are not using reset, control of a high temperature boiler with an alternative source is relatively simple. You just measure the temperature of the wood boiler, and if it drops below a setpoint, you turn off the wood boiler circulator and turn on the Vitola. With solar, utilization of every bit of alternative energy is more important to the payback. The key is switching over without either heat source heating up the water in the other source.

Without knowing how your system is set up, I am completely guessing.